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Exercise can be both anabolic and catabolic for bone tissue. The temporal response of both bone formation and resorption following an acute bout of exercise is not well described. We assayed biochemical markers of bone and calcium metabolism for up to 3 days after military-relevant exercise. In randomized order, male (n=18) and female (n=2) Soldiers (mean±SD; 21.2±4.1 years) performed a 60-minute bout of load carriage (30% body mass; 22.4±3.7 kg) treadmill exercise (EXER) or a resting control trial (REST). Blood samples were collected following provision of a standardized breakfast before (PRE), after (POST) exercise/rest, 1 h, 2 h, and 4 h into recovery. Fasted samples were also collected at 0630 h on EXER and REST and for the next 3 mornings after EXER. Parathyroid hormone and phosphorus were elevated (208% and 128% of PRE, respectively p0.05), and ionized calcium reduced (88% of PRE, p0.05) after EXER. N-terminal propeptide of type 1 collagen, was elevated at POST (111% of PRE, p0.05), and the resorption marker, C-terminal propeptide of type 1 collagen, was elevated at 1 h (153% of PRE, p0.05). Osteocalcin was higher than PRE at 1 through 4 h post EXER (119-120% of PRE, p0.05). Sclerostin and Dickkopf-related protein-1 were elevated only at POST (132% and 121% of PRE, respectively, p0.05) during EXER. Trivial changes in biomarkers during successive recovery days were observed. These results suggest that 60 minutes of load carriage exercise elicits transient increases in bone formation and resorption that return to pre-exercise concentrations within 24 h post-exercise.

Maintaining Mg status may be important for military recruits, a population that experiences high rates of stress fracture during initial military training (IMT). The objectives of this secondary analysis were to (1) compare dietary Mg intake and serum Mg in female and male recruits pre- and post-IMT, (2) determine whether serum Mg was related to parameters of bone health pre-IMT, and (3) whether Ca and vitamin D supplementation (Ca/vitamin D) during IMT modified serum Mg. Females (n 62) and males (n 51) consumed 2000 mg of Ca and 25 μg of vitamin D/d or placebo during IMT (12 weeks). Dietary Mg intakes were estimated using FFQ, serum Mg was assessed and peripheral quantitative computed tomography was performed on the tibia. Dietary Mg intakes for females and males pre-IMT were below the estimated average requirement and did not change with training. Serum Mg increased during IMT in females (0·06 ± 0·08 mmol/l) compared with males (–0·02 ± 0·10 mmol/l; P < 0·001) and in those consuming Ca/vitamin D (0·05 ± 0·09 mmol/l) compared with placebo (0·001 ± 0·11 mmol/l; P = 0·015). In females, serum Mg was associated with total bone mineral content (BMC, β = 0·367, P = 0·004) and robustness (β = 0·393, P = 0·006) at the distal 4 % site, stress–strain index of the polaris axis (β = 0·334, P = 0·009) and robustness (β = 0·420, P = 0·004) at the 14 % diaphyseal site, and BMC (β = 0·309, P = 0·009) and stress–strain index of the polaris axis (β = 0·314, P = 0·006) at the 66 % diaphyseal site pre-IMT. No significant relationships between serum Mg and bone measures were observed in males. Findings suggest that serum Mg may be modulated by Ca/vitamin D intake and may impact tibial bone health during training in female military recruits.

The respiratory burst is a rapid cellular consumption of oxygen resulting in abundant production of reactive oxygen species (ROS), most often associated with primary mediators of innate immunity, neutrophils and macrophages. These myeloid cells convert ROS into potent antimicrobial oxidants that efficiently kill pathogens. The respiratory burst also can have destructive consequences, as ROS are well known to support chronic inflammation and aberrant autoimmune responses. Interestingly, ROS perform conflicting roles in the tumor microenvironment; ROS and derived cytotoxic products can destroy cancer cells but also suppress important tumor-fighting functions of T cells or natural killer cells, or yield mutagenized proteins that can promote tumorigenesis or support tumor cell growth. Moreover, high numbers of neutrophils or macrophages in tumors are associated with poor prognosis. Therefore, accurate and quantitative assays to assess the respiratory burst are an important tool for measuring ROS production by neutrophils or cells of the monocyte/macrophage system, each recently identified in the tumor microenvironment. Described are methods to derive mouse or human models of neutrophils or macrophages, which are then used in a detailed assay to quantitatively measure ROS produced by either cell type using luminescence-enhanced reagents and a multi-well platform along with different stimulants that cause rapid ROS production.

OBJECTIVES: Aerobic exercise (EX) reduces circulating ionized Ca (iCa) and increases parathyroid hormone (PTH), but the cause and consequences on Ca handling are unknown. The objective of this study was to determine the effects of EX on Ca kinetics using dual stable Ca isotopes. METHODS: Twenty-one healthy women (26.2 ± 6.7 yr; BMI: 22.8 ± 2.1 kg/m(2)) completed a randomized, crossover study consisting of two 6 day iterations separated by ≥2 wk. One iteration consisted of 3 d of load carriage EX 2 h after breakfast (1 hr treadmill walking at 65% VO(2max) wearing a vest weighing 30% body wt) on days 0, 2, 4, and the other a no-EX control (CON). Diet was controlled during each iteration, and matched to the volunteer's usual intake. On day 0, volunteers received one IV bolus of (42)Ca, and oral (44)Ca with each meal (0600,1200, and 1700). Serial blood draws and 3 urine pools (U1: 0600–1000, U2: 1000–2000, U3: 2000–0800) were collected on day 0; spot urines were collected on days 1–5. Ca isotope ratios were analyzed by Thermal Ionization Mass Spectrometry and total Ca by Siemens Dimension; fractional Ca absorption (FCA) was measured and kinetic modeling determined, rates of Ca deposition (VO+) and resorption (VO–) from bone, and bone Ca balance (Vbal). Circulating PTH and iCa were also measured before, during and after exercise. Data were analyzed by paired T-test or linear mixed models using SPSS. RESULTS: On day 0, PTH increased 45 min into EX as compared to pre (+36 pg/ml, P 0.05). FCA was greater during EX (26.6 ± 8.1%) compared to CON (23.9 ± 8.3%, P 0.05). CONCLUSIONS: During EX, an increase in FCA and decrease in UCa resulted in a positive shift in Ca balance. The rapid reduction in circulating iCa may be due to a change in the miscible Ca pool, resulting in increased PTH and changes in intestinal and renal Ca handling that support a more positive Ca balance. FUNDING SOURCES: Defense Health Program.

Stress fractures are common overuse injuries caused by repetitive bone loading. These fractures are of particular concern for military recruits and athletes resulting in attrition in up to 60% of recruits that sustain a fracture. Army and Navy recruits supplemented with daily calcium and vitamin D (Ca + D) demonstrated improved bone strength and reduced stress fractures. The aim of the current study was to evaluate whether Ca + D supplementation improves measures of bone health in recruits undergoing United States Marine Corps initial military training (IMT), and whether the effect of supplementation on indices of bone health varied by season. One-hundred ninety-seven Marine recruits (n = 107 males, n = 90 females, mean age = 18.9 ± 1.6 y) were randomized to receive either Ca + D fortified snack bars (2000 mg Ca and 1000 IU vitamin D per day) or placebo divided into twice daily doses during 12 weeks of IMT. Anthropometrics, fasted blood samples, and peripheral quantitative computed tomography (pQCT) scans of the tibial metaphysis and diaphysis were collected upon entrance to- and post-training (12 weeks later). Half of the volunteers entered training in July and the other half started in February. Time-by-group interactions were observed for vitamin D status (25OHD) and the bone turnover markers, BAP, TRAP and OCN. 25OHD increased and BAP, TRAP and OCN all decreased in the Ca + D group (p .05). Training increased distal tibia volumetric BMD (+1.9 ± 2.8%), BMC (+2.0 ± 3.1%), and bone strength index (BSI; +4.0 ± 4.0%) and diaphyseal BMC (+1.0 ± 2.2%) and polar stress strain index (SSIp; +0.7 ± 2.1%) independent of Ca + D supplementation (p .05 for all). When analyzed by season, change in BSI was greater in the Ca + D group as compared to placebo in the summer iteration only (T*G; p .05). No other effects of supplementation on bone tissue were observed. When categorized by tertile of percent change in BSI, recruits demonstrating the greatest changes in BSI and 25OHD entered training with the lowest levels of 25OHD (p .05). Over all, these results suggest that Ca + D supplementation reduced some markers of bone formation and resorption and the decline in 25OHD over training in volunteers that started training in the summer was prevented by supplementation. Baseline 25OHD and trajectory may impact bone responses to IMT, but little effect of Ca + D supplementation was observed at the investigated doses.

Musculoskeletal injuries, such as stress fracture, are responsible for over 10-million lost-duty days among U.S. Army Soldiers. During Basic Combat Training (BCT), an 8- to 10-week program that transforms civilians into Soldiers, women are four times more likely than men to sustain a stress fracture. In this work, we performed high-resolution peripheral quantitative computed tomography scans on the ultradistal tibia of 90 female recruits [age = 21.5 ± 3.3 (mean ± standard deviation) years] before the start of BCT and after 8 weeks into BCT. Then, we divided the scanned bone volume into four sectors—lateral, posterior, medial, and anterior—and computed the bone density and microarchitectural parameters in each of the four sectors pre- and post-BCT. We used linear mixed models to estimate the mean difference for bone density and microarchitectural parameters, while controlling for age, race, and pre-BCT body mass index. Our results revealed that the total volumetric bone mineral density, trabecular volumetric bone mineral density, and trabecular thickness increased (p

Background Stress fracture risk is elevated during initial military training (IMT), particularly in lower-extremity bones such as the tibia. Although the etiology of stress fractures is multifactorial, lower bone strength increases risk. Objective The objective of this study was to assess, through the use of peripheral quantitative computed tomography, whether adherence to a dietary pattern rich in calcium, potassium, and protein before IMT is positively associated with bone indexes in young adults entering IMT. Design A cross-sectional analysis was performed with the use of baseline data from 3 randomized controlled trials in Army, Air Force, and Marine recruits (n = 401; 179 men, 222 women). Dietary intake was estimated from a food-frequency questionnaire. A dietary pattern characterized by calcium, potassium, and protein was derived via reduced rank regression and a pattern z score was computed for each volunteer, where higher scores indicated greater adherence to the pattern. At the 4% (metaphysis) and 14% (diaphysis) sites of the tibia, bone mineral content (BMC), volumetric bone mineral density, robustness, and strength indexes were evaluated. Associations between dietary pattern z score as the predictor variable and bone indexes as the response variables were evaluated by multiple linear regression. Results Pattern z score was positively associated with BMC (P = 0.004) and strength (P = 0.01) at the metaphysis and with BMC (P = 0.0002), strength (P = 0.0006), and robustness (P = 0.02) at the diaphysis when controlling for age, sex, race, energy, smoking, education, and exercise. Further adjustment for BMI attenuated the associations, except with diaphyseal BMC (P = 0.005) and strength (P = 0.01). When height and weight were used in place of body mass index, the association with BMC remained (P = 0.046). Conclusions A dietary pattern rich in calcium, potassium, and protein is positively associated with measures of tibia BMC and strength in recruits entering IMT. Whether adherence to this dietary pattern before IMT affects injury susceptibility during training remains to be determined. These trials were registered at clinicaltrials.gov as NCT01617109 and NCT02636348.

BACKGROUND Vitamin D deficiency (VDD), defined as serum 25-hydroxyvitamin D (25[OH]D) levels < 20 ng/mL [to convert 25[OH]D ng/mL to nmol/L, multiply by 2.5]) is prevalent in young adults and has been associated with adverse health outcomes, including stress fracture during periods of increased physical activity such as military training. Foods commonly consumed at breakfast provide an important source of vitamin D, yet breakfast skipping is common among young adults. However, whether breakfast skipping is associated with VDD in young adults is unclear. OBJECTIVES This study aimed to determine whether breakfast skipping is associated with odds of VDD among recruits entering initial military training (IMT), and with changes in serum 25(OH)D during IMT. In addition, whether diet quality and vitamin D intake mediated these associations was determined. DESIGN Secondary analysis of individual participant data collected during five IMT studies. Breakfast skipping (≥ 3 times/week) was self-reported. Dietary intake was determined using food frequency questionnaires, and vitamin D status was assessed using circulating 25(OH)D concentrations pre- and post-IMT. PARTICIPANTS AND SETTING Participants were healthy US Army, US Air Force, and US Marine recruits (N = 1,569, 55% male, mean ± standard deviation age 21 ± 4 years) entering military service between 2010 and 2015 at Fort Jackson, SC; Fort Sill, OK; Lakeland Air Force Base, TX; or the Marine Corps Recruit Depot, Parris Island, SC. MAIN OUTCOME MEASURES Primary outcomes were VDD pre-IMT and change in 25(OH)D from pre- to post-IMT. STATISTICAL ANALYSIS PERFORMED Associations were determined using multivariate-adjusted logistic and linear regression and mediation models. RESULTS Forty-six percent of military recruits were classified as breakfast skippers pre-IMT, and 30% were VDD. Breakfast skipping was associated with a higher odds of pre-IMT VDD (odds ratio 1.5, 95% CI 1.1 to 1.9), and lower vitamin D intake and diet quality were partial mediators of the association. Serum 25(OH)D concentrations improved (P = 0.01) among habitual breakfast skippers versus nonskippers during IMT; however, regression to the mean could not be ruled out. Neither change in diet quality nor vitamin D intake were associated with change in 25(OH)D concentrations during IMT. CONCLUSIONS Breakfast skipping is prevalent among incoming military recruits and is associated with VDD. This relationship may be mediated by lower diet quality and vitamin D intake.

Basic combat training (BCT) is a period of novel physical training including load carriage resulting in higher risk of stress fracture compared to any other time during military service. Prior trials reported a 20% reduction in stress fracture incidence with Ca and vitamin D (Ca + D) supplementation (2000 mg Ca, 800 IU vitamin D), and greater increases in tibia vBMD during BCT compared to placebo. The primary objective of this randomized, double-blind, placebo-controlled trial was to determine the efficacy of a lower dose of Ca (1000 mg/d Ca, 1000 IU vit D) on PTH, bone biomarkers and tibial microarchitecture during BCT. One hundred volunteers (50 males, 50 females; mean age 21.8 ± 3.5 y) were block randomized by race and sex to receive a daily Ca + D fortified food bar or placebo. Anthropometrics, dietary intake, fasted blood draws and high resolution pQCT scans of the distal and mid-shaft tibia were obtained at the start of BCT and 8 wks later at the conclusion of training. As compliance was 98% in both treatment groups, an intent-to-treat analysis was used. At the distal tibia, total vBMD, Tb.vBMD, Tb.N, Th.Th and Tb.BV/TV increased (+1.07 to 2.12% for all, p 0.05) and Tb.Sp decreased (0.96 to 1.09%, p 0.05) in both treatment groups. At the mid-shaft, Ct.Pm increased (+0.18 to 0.21%, p = 0.01) and Ct.vBMD decreased (-0.48 to -0.77%, p 0.001) in both groups. Ca + D prevented increases in CTX and TRAP, which were observed in the placebo group (group-by-time, p 0.05). Mean circulating 25OHD, BAP, P1NP and iCa increased and PTH decreased in both treatment groups (p 0.05). These results, in agreement with other studies, suggest that bone microarchitectural changes indicative of bone formation occur during BCT. While Ca + D supplementation at lower doses than those tested in previous studies prevented increases in biochemical markers of bone resorption in this study, there were no significant changes in bone tissue after 8 wks of Army BCT.

High-protein diets are generally considered beneficial for calcium (Ca) economy and bone health. Improved intestinal Ca absorption efficiency may be one mechanism by which higher-protein diets affect Ca homeostasis and bone health. The signaling pathways and individual amino acids (AA) responsible for this effect have not been fully elucidated and may involve the transcellular pathway, paracellular pathway or a combination. The primary aim of this study was to investigate whether a mixture of AA and/or functionally distinct individual AA directly affect paracellular Ca absorption across an intestinal epithelial cell model (Caco-2 Bbe). Using Ussing chambers, we examined the effect of six treatments - vehicle (Veh), 80 mM raffinose (Raf; positive control), 2× mixed AA(2×AA, twice the concentration in standard growth media), the branched-chain amino acid leucine (2-10 mM Leu), the aromatic amino acid phenylalanine (2-10 mM Phe) and the dibasic amino acid lysine (2-10 mM Lys) - on Ca flux. Leu (5 mM) increased Ca flux by 38% (+122 nmol Ca/cm2/h, P

U.S. Army Basic Combat Training (BCT) is a physically-demanding program at the start of military service. Whereas animal studies have shown that increased mechanical loading rapidly alters bone structure, there is limited evidence of changes in bone density and structure in humans exposed to a brief period of unaccustomed physical activity.We aimed to characterize changes in tibial bone density and microarchitecture and serum-based biochemical markers of bone metabolism in female recruits as a result of 8 weeks of BCT.We collected high-resolution peripheral quantitative computed tomographic images of the distal tibial metaphysis and diaphysis (4% and 30% of tibia length from the distal growth plate, respectively) and serum markers of bone metabolism before and after BCT. Linear mixed models were used to estimate the mean difference for each outcome from pre- to post-BCT, while controlling for race/ethnicity, age, and body mass index.91 female BCT recruits volunteered and completed this observational study (age = 21.5 ± 3.3 yrs). At the distal tibial metaphysis, cortical thickness, trabecular thickness, trabecular number, bone volume/total volume, and total and trabecular volumetric bone density (vBMD) increased significantly by 1-2% (all p 0.05) over the BCT period, whereas trabecular separation, cortical tissue mineral density (TMD), and cortical vBMD decreased significantly by 0.3-1.0% (all p 0.05). At the tibial diaphysis, cortical vBMD and cortical TMD decreased significantly (both -0.7%, p 0.001). Bone strength, estimated by micro finite element analysis, increased by 2.5% and 0.7% at the distal tibial metaphysis and diaphysis, respectively (both p 0.05). Among the biochemical markers of bone metabolism, sclerostin decreased (-5.7%), whereas bone alkaline phosphatase, C-telopeptide cross-links of type 1 collagen, tartrate-resistance acid phosphatase, and 25(OH)D increased by 10-28% (all p 0.05).BCT leads to improvements in trabecular bone microarchitecture and increases in serum bone formation markers indicative of new bone formation, as well as increases in serum bone resorption markers and decreases in cortical vBMD consistent with intracortical remodeling. Together, these results demonstrate specific changes in trabecular and cortical bone density and microarchitecture following 8 weeks of unaccustomed physical activity in women.

OBJECTIVES: Female military recruits are at risk for developing stress fractures during initial military training (IMT). Accurate assessment of both calcium (Ca) and vitamin D (vit D) intake may support the development of targeted dietary interventions for those at risk of deficiency. The objective of this study was to investigate the relationships between different dietary assessment methods for estimated dietary Ca and vit D intakes in a healthy population. METHODS: Active, healthy females (18–42 yr, 19–26 kg/m(2) body mass index) recruited for an exercise study were included. Study dietitians administered: three 24-hour recalls (24HR) (baseline and before two exercise interventions), full-length Block 2014 Food Frequency Questionnaire (FFQ) (baseline), and Block Calcium and Vitamin D Screener (baseline). Twenty-four HR data were averaged and then quantified by Food Processor SQL. Block questionnaires were analyzed by NutritionQuest. Ca and vit D intakes were energy adjusted using the density method for all assessment methods except the screener. Means, standard deviations (SD), and correlations between 24HR variables were analyzed using SPSS. RESULTS: Twenty-one participants completed the study: (mean ± SD) 26.2 ± 6.7 yr, 22.76 ± 2.12 kg/m(2). Estimated intakes from the 24HR, FFQ, and screener for Ca (mg/d) were 741 ± 403,1001 ± 420, and 446 ± 270, respectively and for vit D (μg/d) were 2.8 ± 3, 4.6 ± 2.6, and 1.8 ± 1.6, respectively. Moderate, positive correlations were found between the 24HR and unadjusted FFQ Ca intake (r = 0.636, P = 0.002), and the 24HR and adjusted FFQ vit D intake (r = 0.561, P = 0.008). No significant correlations were observed between the nutrients of interest as measured by the 24HR and screener. CONCLUSIONS: Intake estimates of Ca and vit D from the full-length FFQ displayed moderate agreement with those estimated by the 24HR, and the FFQ produced relatively higher estimates. Given this, the FFQ may be more practical for use in an IMT setting, for estimating relative Ca and vit D intakes, than the 24HR to identify individuals who may benefit from interventions promoting bone health. FUNDING SOURCES: Defense Health Program. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.

Background The 2010 Healthy Eating Index (HEI-2010), a measure of diet quality, is used to quantify adherence to the Dietary Guidelines for Americans. Better HEI scores have been associated with positive health outcomes; however, the relationship between diet quality and psychological resilience, a mental health attribute for coping with adversity, has not been assessed. Objective The objective of the present study was to assess the relationship between diet quality and psychological resilience, and the relationship between resilience and demographics, anthropometrics, socioeconomic status, and health behavior. Design In this cross-sectional study, HEI-2010 scores and resilience were assessed using the Block food frequency questionnaire and the Connor-Davidson Resilience Scale. Other factors that can affect the relationship between HEI-2010 scores and resilience were assessed using surveys, and height and weight were measured to calculate body mass index. Participants/setting Male and female Army and Air Force recruits (n=834) enrolled in a randomized controlled trial and 656 (mean±standard deviation [SD] age=21±3.3 years) were included in this analysis. Data were collected before the initiation of military training at Fort Sill, OK (2012-2013) and Lackland Air Force Base, TX (2013-2014). Statistical analysis performed Participants were split into low- and high-resilience groups based on Connor-Davidson Resilience Scale scores. Student's t test and χ 2 tests were used to determine differences between groups for continuous and categorical variables, respectively. Logistic regression was utilized to identify predictors of resilience. Results Better diet quality was associated with resilience; higher HEI predicted an increased likelihood (odds ratio=1.02; 95% CI 1.01 to 1.04) of a participant being in the high-resilience group after including race, ethnicity, education, smoking, age, body mass index, sex, and military branch in the full model. The data indicate that with every 10-point increase in HEI score, there was a 22% increased likelihood of being in the high-resilience group. Conclusions Registered dietitian nutritionists should continue to encourage attainable changes to improve diet; study data suggest that small improvements in diet quality can be associated with better psychological resilience.

Background Musculoskeletal injuries (MSKIs) are common in military trainees and present a considerable threat to occupational fitness, deployability, and overall military readiness. Despite the negative effects of MSKIs on military readiness, comprehensive evaluations of the key known and possible risk factors for MSKIs are lacking. The U.S. Army Research Institute of Environmental Medicine (ARIEM) is initiating a large-scale research effort, the ARIEM Reduction in Musculoskeletal Injury (ARMI) Study, to better understand the interrelationships among a wide range of potential MSKI risk factors in U.S. Army trainees in order to identify those risk factors that most contribute to MSKI and may be best targeted for effective mitigation strategies. Methods This prospective study aims to enroll approximately 4000 (2000 male and 2000 female) U.S. Army trainees undergoing Basic Combat Training (BCT). Comprehensive in-person assessments will be completed at both the beginning and end of BCT. Participants will be asked to complete surveys of personal background information, medical history, physical activity, sleep behaviors, and personality traits. Physical measurements will be performed to assess anthropometrics, tibial microarchitecture and whole body bone mineral density, muscle cross-sectional area, body composition, and muscle function. Blood sampling will be also be conducted to assess musculoskeletal, genetic, and nutritional biomarkers of risk. In addition, participants will complete weekly surveys during BCT that examine MSKI events, lost training time, and discrete risk factors for injury. Participants’ medical records will be tracked for the 2 years following graduation from training to identify MSKI events and related information. Research hypotheses focus on the development of a multivariate prediction model for MSKI. Discussion Results from this study are expected to inform current understanding of known and potential risk factors for MSKIs that can be incorporated into solutions that optimize Soldier health and enhance military readiness.

Eating behaviors such as eating fast and ignoring internal satiety cues are associated with overweight/obesity, and may be influenced by environmental factors. This study examined changes in those behaviors, and associations between those behaviors and BMI, cardiometabolic biomarkers, and diet quality in military recruits before and during initial military training (IMT), an environment wherein access to food is restricted. Eating rate and reliance on internal satiety cues were self-reported, and BMI, body fat, cardiometabolic biomarkers, and diet quality were measured in 1389 Army, Air Force and Marine recruits (45% female, mean ± SEM BMI = 24.1 ± 0.1 kg/m2) before and after IMT. Pre-IMT, habitually eating fast relative to slowly was associated with a 1.1 ± 0.3 kg/m2 higher BMI (P

The objective of the study was to evaluate how controlled, short-term sleep restriction (SR; 72 h) alters markers of bone formation and resorption and urinary calcium (Ca) output. Ten healthy, sleep-adequate, male soldiers were housed in the research facility one day prior to and for the duration of SR. Diet was controlled to provide adequate energy balance and macronutrient distribution, meeting the recommended dietary allowance (RDA) for Ca. Subjects engaged in light activities to maintain wakefulness and were allowed 2 h of sleep per night (0430–0630 hours). Blood samples were collected each morning at 0 h (baseline) and 24, 48, and 72 h of SR. Serum was assayed for parathyroid hormone (PTH), bone alkaline phosphatase (BAP), tartrate-resistant acid phosphatase (TRAP), and C-terminal telopeptide of type I collagen (CTX). Urine was collected in 24 h increments during SR for measurement of Ca and creatinine (Cr). BAP was reduced at 24 h (P= 0.015) and resorption markers TRAP and CTX were increased after 48 and 72 h of SR compared to baseline (P

Military personnel train and conduct operations in environments that result in exposure to multiple stressors such as caloric deprivation, physical and psychological strain, and increased energy expenditure, which have profound effects on cognitive and physical performance. The objective of this chapter is to draw on the peer-reviewed literature, including laboratory studies, applied field studies, and controlled trials conducted in the military environment to detail the contribution of nutrition and genetics to human performance and protection from injury. In summary, relevant studies indicate that nutrition status and genetic factors hold promise as risk biomarkers and intervention targets for the development of tailored solutions to optimize human performance and prevent injury during occupationally demanding tasks.

Food frequency questionnaires (FFQs) estimate habitual dietary intake and require evaluation in populations of interest in order to determine accuracy. Thus, the purpose of this study was to determine agreement between circulating biomarkers and FFQ estimated dietary intake in a military population consuming all meals in a dining facility over 12 weeks.2014 Block FFQs were administered and fasted blood samples were drawn to assess nutritional biomarkers at the end of a 12-week training period in male (n = 141) and female (n = 125) Marine recruits undergoing initial military training. FFQ estimates of alpha- and beta-carotene, folate, and fruit and vegetable intake and circulating concentrations of serum alpha- and beta-carotene and serum and erythrocyte folate were measured. Partial correlations were used in the full model, and weighted kappa coefficients were used to determine agreement between ranking quartiles of dietary intake estimates with corresponding biomarker status quartiles.Serum and dietary intake of alpha-carotene were positively associated in males (p = 0.009) and females (p 0.001), as was serum and intake of beta-carotene (males, p = 0.002; females, p 0.001). Alpha-carotene was positively associated with vegetable intake in males (p = 0.02) and beta-carotene with vegetable intake in females (p = 0.003). Serum folate in males (p = 0.002) and erythrocyte folate in females (p = 0.02) were associated with dietary folate intake. In females, the relationships between biomarker and dietary estimates yielded significant kappa coefficients. In males, a significant kappa coefficient was observed for erythrocyte folate and dietary intake of folate only. The kappa coefficient for serum and estimated intake of beta-carotene was not significant in males.Twelve-week habitual intake of alpha-and beta-carotene and folate were correlated with circulating biomarkers in a military training population. The 2014 Block FFQ was able to accurately rank females into quartiles of nutrient status based on intake, while males were ranked less accurately than females.

Initial military training (IMT) is associated with increased stress fracture risk. In prior studies, supplemental calcium (Ca) and vitamin D provided daily throughout IMT reduced stress fracture incidence, suppressed PTH, and improved measures of bone health compared to placebo. Data were analyzed from a randomized, double-blind, placebo-controlled trial to determine whether SNPs in Ca and vitamin D related genes were associated with circulating biomarkers of bone metabolism in young adults entering IMT, and whether responses to Ca and vitamin D supplementation were modulated by genotype. Associations between SNPs including: vitamin D receptor (VDR), vitamin D binding protein (DBP), and 1-alpha-hydroxylase (CYP27B1), and circulating biomarkers were measured in fasting blood samples from volunteers (n = 748) starting IMT. Volunteers were block randomized by race and sex to receive Ca (2000 mg) and vitamin D (1000 IU) or placebo daily throughout Army or Air Force IMT (7-9 wk). Total Ca and vitamin D intakes were calculated as the sum of supplemental intake based on intervention compliance and dietary intake. Relationships between SNPs, Ca and vitamin D intake tertile, and change in biomarkers were evaluated in trial completers (n = 391). At baseline, the minor allele of a DBP SNP (rs7041) was positively associated with both 25OHD (B = 4.46, p = 1.97E-10) and 1,25(OH)2D3 (B = 9.63, p =

Nutrition is essential for maintaining peak health and performance of Warfighters. This review will focus on a series of nutrients of concern for female Warfighters. Biological function, dietary sources, and requirements will be reviewed, and recommendations for women in combat roles will be provided. Iron, essential for physical and cognitive performance, is critical for female Warfighters because of elevated dietary requirements as compared to male Warfighters, as well as declines in iron status that may occur in response to physical activities, such as military training. Calcium and vitamin D are essential for bone health, and should be considered in efforts to prevent stress fractures, which occur with greater frequency in female Warfighters as compared to their male counterparts. Folate, essential for the prevention of neural tube defects during pregnancy and gestation, is critical for female Warfighters because of elevated dietary requirements before pregnancy. Providing optimal levels of these nutrients will facilitate readiness as women prepare to serve in combat roles.

Ca/vitamin D supplementation maintains bone health and decreases stress fracture risk during initial military training (IMT); however, there is evidence that Ca may negatively affect the absorption of other critical micronutrients, particularly Fe. The objective of this randomised, double-blind, placebo-controlled trial was to determine whether providing 2000 mg/d Ca and 25µg/d vitamin D in a fortified food product during 9 weeks of military training affects Fe status in young adults. Male (n98) and female (n54) volunteers enrolled in US Army basic combat training (BCT) were randomised to receive a snack bar with Ca/vitamin D (n75) or placebo (snack bar without Ca/vitamin D;n77) and were instructed to consume 2 snack bars/d between meals throughout the training course. Circulating ionised Ca was higher (PPPP>0·05) in markers of Fe status between placebo and Ca/vitamin D groups. Collectively, these data indicate that Ca/vitamin D supplementation through the use of a fortified food product consumed between meals does not affect Fe status during IMT.

OBJECTIVES: Vitamin D deficiency (VDD) and iron deficiency (ID) are associated with injury risk and performance, respectively, in military recruits during initial military training (IMT). Breakfast skipping is prevalent among young adults and contributes to decreased intakes of vitamin D and iron. However, whether breakfast skipping is associated with VDD and ID in military recruits, and whether the mandatory breakfast attendance required in IMT mitigates VDD and ID is unknown. METHODS: Army, Air Force, and Marine recruits (N = 2117, 42% male, mean ± SD age 21 ± 4y) completed a food frequency questionnaire pre-IMT, and provided blood samples pre- and post-IMT. Breakfast skipping was self-reported and defined as skipping breakfast ≥3 d/wk pre-IMT. Diet quality was determined by Healthy Eating Index. ID was defined as meeting ≥2 of the following: serum ferritin 15%. VDD was defined as serum 25-hydroxyvitamin D (25OHD)

Vitamin D's role in regulating immune responses may increase during periods of elevated psychological and physiological stress. Due to the high demands placed on US Marine Corps recruits undergoing 12 weeks of basic military training, we hypothesized that vitamin D status would be related to markers of innate mucosal immunity, and daily vitamin D supplementation would augment immune responses during training. Males (n = 75) and females (n = 74) entering recruit basic training during the summer and winter volunteered to participate in a randomized, double-blind, placebo-controlled study. Subjects received either 1000 IU vitamin D3 + 2000 mg calcium/d (n = 73) or placebo (n = 76) for 12 weeks. Saliva samples were collected pre-training, during (weeks 4 and 8), and post-training (week 12) in order to determine salivary SIgA and cathelicidin (indices of mucosal immunity) and α-amylase (indicator of stress). Initial (baseline) and post-training serum 25(OH)D levels were measured. Results were as follows: serum 25(OH)D levels were 37% higher in recruits entering training in summer compared with winter. A positive relationship was observed between baseline 25(OH)D levels and SIgA secretion rates (-SR). When stress levels were high during summer training, baseline 25(OH)D levels contributed to an increase in salivary secretory immunoglobulin A secretion rates (SIgA-SR) and cathelicidin-SR, the latter only in males. Vitamin D supplementation contributed to the changes in SIgA-SR and cathelicidin-SR, specifically SIgA-SR was higher in the treatment group. These data highlight the importance of vitamin D and mucosal immune responses during arduous basic military training when stress levels are increased.

The aim of this study was to determine whether an acute bout of exercise reduces serum sclerostin under diet‐controlled conditions that stabilize the parathyroid hormone (PTH)‐1,alpha‐hydroxylase axis. Fourteen male volunteers (age, 22.1 years ± 4.05; BMI, 27.3 kg/m2 ± 3.8) completed a randomized crossover study in which they performed 10 sets of 10 repetitions of plyometric jumps at 40% of their estimated one‐repetition maximum leg press or a nonexercise control period. A calcium‐controlled diet (1000 mg/day) was implemented prior to, and throughout each study period. Blood was drawn for analysis of serum sclerostin, Dickkopf‐1, markers of bone metabolism (PTH, calcium), markers of bone formation (bone alkaline phosphatase, BAP; osteocalcin, OCN), and markers of bone resorption (tartrate‐resistant acid phosphatase 5b, TRAP5b; C‐telopeptide cross‐links of type I collagen, CTX) at baseline and 12, 24, 48, and 72 h following exercise or rest. Changes in serum concentrations were expressed as percentage change from individual baselines. Data were analyzed using a repeated measured linear mixed model to assess effects of time, physical activity status (rest or exercise condition), and the time by activity status interaction. There was a significant effect of exercise on OCN (P = 0.005) and a significant interaction effect for CTX (P = 0.001). There was no effect of exercise on any other biochemical marker of bone metabolism. A single bout of plyometric exercise did not induce demonstrable changes in biochemical markers of bone metabolism under conditions where dietary effects on PTH were controlled.

Introduction The military dietary reference intakes (MDRIs), outlined in Army Regulation 40-25, OPNAVINST 10110.1/MCO10110.49, AFI 44-141, establish standards intended to meet the nutrient requirements of Warfighters. Therefore, the purpose of this study was to comprehensively compare the revised MDRIs, published in 2017, with estimated dietary intakes in U.S. military personnel. Materials and methods During this cross-sectional study, Block food frequency questionnaires were administered at the end of the 9-week basic combat training course to estimate dietary intake during basic combat training in male (n = 307) and female (n = 280) recruits. The cut-point method was used to determine nutrient adequacy in comparison to the MDRIs. This study was approved by the Institutional Review Board of the U.S. Army Research Institute of Environmental Medicine. Results Recruits consumed an adequate amount of vitamins A, C and K, as well as the B-vitamins, and phosphorus, selenium, zinc, and protein and carbohydrate as a percentage of total calories when compared with MDRI standards. Vitamin D was the short-fall nutrient affecting the greatest number of participants, as 55 and 70% of males and females, respectively, consumed less than 33% of the MDRI. In addition, less than 50% of males met the MDRI for linoleic and α-linolenic acid, fiber, vitamin E, magnesium, and potassium, and less than 50% of females met the MDRI for α-linolenic acid, fiber, vitamin E, calcium, iron, magnesium, and potassium. In contrast, fat and sodium were over-consumed by both males (78 and 87%, respectively) and females (73 and 72%, respectively). Conclusion The main findings of this study were that vitamins D and E, magnesium, potassium, α-linolenic acid, and fiber were under consumed by male and female recruits while males also did not consume adequate linoleic acid and females did not consume adequate calcium and iron. Future prospective research studies are needed to determine possible health and performance impacts that may be associated with suboptimal intake of these nutrients.

Context:It has been assumed that the increase in urine calcium (Ca) that accompanies an increase in dietary protein was due to increased bone resorption. However, studies using stable Ca isotopes have found that dietary protein increases Ca absorption without increasing bone resorption.Objective:The objective of the study was to investigate the impact of a moderately high protein diet on bone mineral density (BMD).Design:This was a randomized, double-blind, placebo-controlled trial of protein supplementation daily for 18 months.Setting:The study was conducted at two institutional research centers.Participants:Two hundred eight older women and men with a body mass index between 19 and 32 kg/m2 and a self-reported protein intake between 0.6 and 1.0 g/kg participated in the study.Intervention:Subjects were asked to incorporate either a 45-g whey protein or isocaloric maltodextrin supplement into their usual diet for 18 months.Main Outcome Measure:BMD by dual-energy x-ray absorptiometry, body composition, and markers of skeletal and mineral metabolism were measured at baseline and at 9 and 18 months.Results:There were no significant differences between groups for changes in L-spine BMD (primary outcome) or the other skeletal sites of interest. Truncal lean mass was significantly higher in the protein group at 18 months (P = .048). C-terminal telopeptide (P = .0414), IGF-1 (P = .0054), and urinary urea (P < .001) were also higher in the protein group at the end of the study period. There was no difference in estimated glomerular filtration rate at 18 months.Conclusion:Our data suggest that protein supplementation above the recommended dietary allowance (0.8 g/kg) may preserve fat-free mass without adversely affecting skeletal health or renal function in healthy older adults.

Submariners spend prolonged periods submerged without sunlight exposure and may benefit from vitamin D supplementation to maintain vitamin D status. The primary objective of this study was to determine the efficacy of daily vitamin D supplementation on maintenance of 25-hydroxyvitamin D (25(OH)D) during a 3-month submarine patrol. Submariners were randomly divided into three groups: placebo (n = 16), 1,000 IU/day (n = 20), or 2,000 IU/day (n = 17). Anthropometrics, self-reported dietary calcium and vitamin D intake, serum markers of vitamin D and bone metabolism, and peripheral quantitative computed tomography (pQCT) parameters of the tibia were determined before and after the patrol. Prior to departure, 49 % of the subjects were vitamin D insufficient (

Iron (Fe) deficiency is endemic worldwide. Little data are available regarding acute effects of dietary protein on intestinal Fe absorption. The current study evaluated the short-term effects of increasing dietary protein on Fe absorption and expression of genes involved in Fe homeostasis. Sprague Dawley rats (24, female) were randomly assigned to custom-formulated isocaloric diets containing 40, 20 (control), or 5% protein (as percentage of total kilocalories) for 7 d. Whole-body Fe balance studies demonstrated that Fe retention was greater in the 40% group than in the 5% group (30.8 vs. 7.3%; P0.01). In a separate study utilizing stable iron isotopes, the 40% group absorbed 30% of ingested Fe, while the 20% group absorbed 18% (P=0.005). Whole-genome profiling revealed that increasing dietary protein from 5 to 40% increased duodenal transcript expression of divalent metal transporter 1 (DMT1) 3.2-fold, duodenal cytochrome b (Dcytb) 1.8-fold, and transferrin receptor (TfR) 1.8-fold. Consistent with these findings, DMT1 transcript expression was 4-fold higher in RNA prepared from duodenal mucosa in the 40% group compared to the 20% group (P0.001). These data suggest that increasing dietary protein increases intestinal Fe absorption in part by up-regulating DMT1, Dcytb, and TfR.

Purpose of review To summarize recent findings regarding the effects of inflammation on iron (Fe) metabolism and to review studies detailing the influence of poor Fe status on physical and cognitive performance. Recent findings Hepatic expression and release of hepcidin, a negative regulator of Fe status, is increased by the actions of the inflammatory cytokine interleukin-6. Inflammation associated with chronic disease, obesity, and exercise is associated with elevated interleukin-6 and hepcidin levels, which may result in diminished Fe status. Summary Decrements in Fe status due to insufficient dietary Fe intake and/or the inflammatory response may degrade physical and cognitive performance. Future studies should clarify whether dietary or other therapeutic interventions to mitigate inflammation attenuate hepcidin-mediated declines in Fe status.

The purpose of this investigation was to assess the influence of calorie restriction (CR) alone, higher-protein/lower-carbohydrate intake alone, and combined CR higher-protein/lower-carbohydrate intake on glucose homeostasis, hepatic de novo lipogenesis (DNL), and intrahepatic triglycerides. Twelve-week old male Sprague Dawley rats consumed ad libitum (AL) or CR (40% restriction), adequate (10%), or high (32%) protein (PRO) milk-based diets for 16 weeks. Metabolic profiles were assessed in serum, and intrahepatic triglyceride concentrations and molecular markers of de novo lipogenesis were determined in liver. Independent of calorie intake, 32% PRO tended to result in lower homeostatic model assessment of insulin resistance (HOMA-IR) values compared to 10% PRO, while insulin and homeostatic model assessment of β-cell function (HOMA-β) values were lower in CR than AL, regardless of protein intake. Intrahepatic triglyceride concentrations were 27.4 ± 4.5 and 11.7 ± 4.5 µmol·g−1 lower (p < 0.05) in CR and 32% PRO compared to AL and 10% PRO, respectively. Gene expression of fatty acid synthase (FASN), stearoyl-CoA destaurase-1 (SCD1) and pyruvate dehydrogenase kinase, isozyme 4 (PDK4) were 45% ± 1%, 23% ± 1%, and 57% ± 1% lower (p < 0.05), respectively, in CR than AL, regardless of protein intake. Total protein of FASN and SCD were 50% ± 1% and 26% ± 1% lower (p < 0.05) in 32% PRO compared to 10% PRO, independent of calorie intake. Results from this investigation provide evidence that the metabolic health benefits associated with CR—specifically reduction in intrahepatic triglyceride content—may be enhanced by consuming a higher-protein/lower-carbohydrate diet.

Initial military training (IMT) is associated with increased stress fracture risk. In prior studies, supplemental calcium (Ca) and vitamin D provided daily throughout IMT reduced stress fracture incidence, suppressed parathyroid hormone (PTH), and improved measures of bone health compared with placebo. Data were analyzed from a randomized, double-blind, placebo-controlled trial to determine whether single-nucleotide polymorphisms (SNPs) in Ca and vitamin D-related genes were associated with circulating biomarkers of bone metabolism in young adults entering IMT, and whether responses to Ca and vitamin D supplementation were modulated by genotype. Associations between SNPs, including vitamin D receptor (VDR), vitamin D binding protein (DBP), and 1-alpha-hydroxylase (CYP27B1), and circulating biomarkers were measured in fasting blood samples from volunteers (n = 748) starting IMT. Volunteers were block randomized by race and sex to receive Ca (2000 mg) and vitamin D (1000 IU) or placebo daily throughout Army or Air Force IMT (7 to 9 weeks). Total Ca and vitamin D intakes were calculated as the sum of supplemental intake based on intervention compliance and dietary intake. Relationships between SNPs, Ca, and vitamin D intake tertile and change in biomarkers were evaluated in trial completers (n = 391). At baseline, the minor allele of a DBP SNP (rs7041) was positively associated with both 25OHD (B = 4.46, p = 1.97E-10) and 1,25(OH)

Acute high protein intake results in increased intestinalcalcium absorption in humans and animals. Calcium is absorbed through both passive paracellular and facilitated trans cellular pathways. In rats, the increase in intestinal calcium absorption observed during a high protein dietis mediated at least in part through increased apical intestinal calcium uptake suggesting involvement of the transcellular pathway. However, we previously found that the expression of a paracellular calcium-permissive tight junction protein, Claudin-2, is higher in the duodenum of rats consuming a high compared to lowprotein diet. Whether dietary protein affects paracellular calcium flux has not been evaluated. Furthermore, the bioactive amino acids that might underlie this effect have not been identified. The purpose of this study was to evaluate the direct effects of mixed and individual amino acids on paracellular calcium flux across a small intestinal absorptive cell model. MethodsCaco-2 Bbe cells were used as a model of ...

Confined space, limited exercise equipment, rotating shift work and reduced sleep may affect cardiometabolic health in submariners. To test this hypothesis, 53 male U.S. Submariners (20–39 years) were studied before and after a 3-month routine submarine patrol. Measures included anthropometrics, dietary and physical activity, biomarkers of cardiometabolic health, energy and appetite regulation, and inflammation. Before deployment, 62% of submariners had a body fat % (BF%) ≥ 25% (obesity), and of this group, 30% met the criteria for metabolic syndrome. In obese volunteers, insulin, the homeostatic model assessment of insulin resistance (HOMA-IR), leptin, the leptin/adiponectin ratio, and pro-inflammatory chemokines growth-related oncogene and macrophage-derived chemokine were significantly higher compared to non-obese submariners. Following the patrol, a significant mean reduction in body mass (5%) and fat-mass (11%) occurred in the obese group as a result of reduced energy intake (~2000 kJ) during the patrol; and, independent of group, modest improvements in serum lipids and a mean reduction in interferon γ-induced protein 10 and monocyte chemotactic protein 1 were observed. Since 43% of the submariners remained obese, and 18% continued to meet the criteria for metabolic syndrome following the patrol, the magnitude of weight loss was insufficient to completely abolish metabolic dysfunction. Submergence up to 3-months, however, does not appear to be the cause of obesity, which is similar to that of the general population.

Male and female C57Bl6 mice were fed a control AIN76A diet, a new Western-style diet (NWD1) reflecting dietary patterns linked to elevated colon cancer incidence (higher fat, lower cholecalciferol, calcium, methyl donors, fiber), or NWD1 with elevated cholecalciferol and calcium (NWD2) from weaning. After 24 wk, serum 25-hydroxyvitamin D [25(OH)D] decreased by >80% in the NWD1 group compared with controls, but with no alteration in serum calcium or bone mineral density. The decreased serum 25(OH)D was prevented in the NWD2 group. After 32 wk, the NWD1 group compared with controls reduced overall energy expenditure by 15% without altering food consumption or physical activity and induced glucose intolerance, phenotypes associated with metabolic syndrome. These responses were unexpectedly exacerbated in the NWD2 group, further shifting mice toward greater fatty acid storage rather than oxidation compared with both control and NWD1 groups, but there was no change in physical activity, causing significant weight gain due to increased fat mass. The NWD1 group also exhibited inflammatory responses compared with controls, including macrophage-associated crown-like structures in epididymal adipose tissue and increased serum concentrations of the proinflammatory cytokine IL-1β, and of its targets, MCP-1 and Rantes, which were prevented or greatly mitigated in the NWD2 group. However, there was also elevated lipid storage in the liver and steatosis not seen in the control and NWD1 groups. Thus, elevating cholecalciferol and calcium in a Western-style diet can reduce inflammation associated with risk for colon tumor development, but interaction of nutrients in this diet can compromise liver function when fed long term.

Proton pump inhibitors (PPIs) are the most potent gastric acid suppressing drugs available, and their use is widespread. An emerging concern about chronic PPI therapy is whether these drugs impair intestinal calcium absorption, resulting in a negative calcium balance and thereby potentially causing bone loss. The objective of this study was to evaluate the acute effect of the PPI esomeprazole or placebo on intestinal calcium absorption in healthy adults. Twelve young adults participated in a placebo-controlled, double-blind, crossover study. There were two 3-week interventions that included a 14-day adjustment period (designed to stabilize calcium homeostasis) followed by 6 days of a diet containing 800 mg of calcium and 2.1 g/kg of protein (intervention). During the last 3 days of the adjustment period and throughout the intervention period, subjects consumed esomeprazole or placebo. Half the subjects underwent 24-hour continuous gastric acid pH monitoring. Intestinal calcium absorption was measured using dual-stable calcium isotopes at the end of each intervention. Treatment with esomprazole significantly increased gastric pH (mean pH on PPI 5.38 +/- 0.13, mean pH on placebo 2.70 +/- 0.44, p = .005). Neither calcium absorption (PPI 34.2% +/- 2.4%, placebo 31.5% +/- 2.1%, p = .24) nor urinary calcium (PPI 321 +/- 38 mg/34 hours, placebo 355 +/- 37 mg/34 hours, p = .07) differed between the PPI and placebo groups. It is concluded that short-term gastric acid suppression by PPIs does not attenuate intestinal calcium absorption in healthy young adults.

Osteoporosis and sarcopenia are degenerative diseases frequently associated with aging. The loss of bone and muscle results in significant morbidity, so preventing or attenuating osteoporosis and sarcopenia is an important public health goal. Dietary protein is crucial for development of bone and muscle, and recent evidence suggests that increasing dietary protein above the current Recommended Dietary Allowance (RDA) may help maintain bone and muscle mass in older individuals. Several epidemiological and clinical studies point to a salutary effect of protein intakes above the current RDA (0.8 g/kg per day) for adults aged 19 and older. There is evidence that the anabolic response of muscle to dietary protein is attenuated in elderly people, and as a result, the amount of protein needed to achieve anabolism is greater. Dietary protein also increases circulating insulin-like growth factor, which has anabolic effects on muscle and bone. Furthermore, increasing dietary protein increases calcium absorption, which could be anabolic for bone. Available evidence supports a beneficial effect of short-term protein intakes up to 1.6 to 1.8 g/kg per day, although long-term studies are needed to show safety and efficacy. Future studies should employ functional measures indicative of protein adequacy, as well as measures of muscle protein synthesis and maintenance of muscle and bone tissue, to determine the optimal level of dietary protein. Given the available data, increasing the RDA for older individuals to 1.0 to 1.2 g/kg per day would maintain normal calcium metabolism and nitrogen balance without affecting renal function and may represent a compromise while longer-term protein supplement trials are pending.

Initial military training (IMT) is associated with elevated bone turnover and an increased risk for stress fractures. Supplemental Ca and vitamin D during IMT improves bone health, although previous studies indicate that supplemental Ca intake may interfere with iron absorption, affecting iron status. The objective of this study was to determine the effect of daily Ca and vitamin D supplementation (2000 mg and 1000 IU/day, respectively) on biochemical indicators of iron status during IMT. Biomarkers (hemoglobin, Hgb; serum ferritin, SF; soluble transferrin receptor, sTfR; transferrin saturation TS) were assessed in fasted volunteers (n = 152, males = 98, females = 54; age [mean ± SD] = 21 ± 4 yrs) at the start and end of a 9-wk IMT course. Supplemental Ca and vitamin D were provided in a fortified snack food, which was consumed between meals 2x/day throughout IMT. Iron status declined over the course, as Hgb, SF and TS declined (8, 50, and 37%, respectively; P < 0.05; main effect of time) and sTfR increas...

Stress fracture incidence is high during initial military training (IMT) with 2-6% of male and 8-21% of female recruits sustaining fractures. Identification and mitigation of risk factors is critic...