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The relationship between calcium (Ca) intake and Ca retention in adolescent boys was recently reported.This study evaluated the influence of Ca intake, serum hormone levels, biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness on Ca retention in the same sample.This study was a randomized, cross-over design that consisted of two 3-wk metabolic balance periods.The study took place on a university campus as a summer camp.A total of 31 American white boys (13-15 yr) participated in the study.Each subject consumed a controlled diet with one of five high-low Ca intake pairs that ranged from 670-2003 mg/d, which was manipulated utilizing a fortified beverage.Ca retention was determined by Ca intake minus urinary and fecal Ca excretion during each balance period.Ca intake explained 21.7% of the variability in Ca retention, and serum IGF-I concentration explained an additional 11.5%. Other serum hormone levels did not significantly add to the model. Biomarkers of bone metabolism, habitual physical activity, habitual Ca intake, and physical fitness were not significant predictors of Ca retention in adolescent boys.IGF-I, a regulator of growth during puberty, is an important predictor of Ca retention in adolescent boys. However, dietary Ca intake is an even greater predictor of Ca retention during this period of growth.

The effects of honey and its carbohydrate constituents (glucose, fructose, and raffinose) on calcium absorption in rats were investigated in acute and chronic feeding studies. In the acute study, rats ( n = 120) were gavaged with an oral solution consisting of (a) 10 microCi (45)Ca, (b) 25 mg of calcium as calcium acetate, and (c) one of the following: 0 mg of honey (control), or 200, 500, or 800 mg of honey, a glucose-fructose mixture, 10.75 mg of raffinose, or 200 mg of raffinose. Another group received (45)Ca intraperitoneally. Femurs were collected 2 days later and analyzed for (45)Ca content. Rats given 500 and 800 mg of honey showed 25.5 and 33.6% increases in calcium absorption ( P

This controlled feeding study examined the effects of exercise on daily water intake (particularly ad libitum water intake), water output, whole-body water balance, and hydration status in physically active, premenopausal women.The randomized crossover design consisted of three 8-day trials: placebo and no exercise, placebo and exercise (1-hour cycling bout per day at 65%-70% of heart rate reserve), and 800 mg calcium supplementation and exercise. During each trial, controlled quantities of the same foods and beverages were provided and ad libitum water intake was quantified. Water input included measured water from foods and beverages, measured ad libitum intake, and estimated metabolic production. Water output included measured losses in urine and stool, and estimated insensible losses from respiration and non-sweating perspiration (insensible diffusion through the skin).Participants were 26 women, age 25+/-5 years, body mass index 22+/-2, and VO(2peak) 43+/-6 mLxkg(-1)xmin(-1) (mean+/-standard deviation).Ad libitum water intake was 363 g/day more (P0.05) for the placebo and exercise (1,940+/-654 g/day) and calcium supplementation and exercise (1,935+/-668 g/day) trials, compared with placebo and no exercise trial (1,575+/-667 g/day), and total water input was correspondingly higher in placebo and exercise and calcium supplementation and exercise trials compared with the placebo and no exercise trial. Urine, stool, and total water outputs were not different among trials. Apparent net water balance (representative of sweat water output) was 367 g/day more (P0.05) in placebo and exercise (679+/-427 g/day) and calcium supplementation and exercise (641+/-519 g/day) trials compared with placebo and no exercise trial (293+/-419 g/day). Hydration status was clinically normal during all three trials. Calcium supplementation did not influence water balance.These results support that young, physically active women can completely compensate for exercise-induced sweat losses by increasing ad libitum water intake, and not decreasing non-sweat water outputs or impairing hydration status.

The aim of this work was to evaluate zinc and iron bioavailability of UFV-116, a new variety without 2 lipoxygenases, with better taste and flavor than a commercial variety OCEPAR 19, containing all 3 isozymes. To evaluate zinc absorption using 65Zn whole body retention and femur 65Zn uptake, rats were given 3 g of a 65ZnCl2 labeled test meal (0.25 microCi). The 2 varieties were tested at the level of 9 and 30 ppm of zinc as defatted soy flour. Two other groups (control) received egg white as source of protein and ZnS04.H20 as the zinc source. To evaluate iron absorption, using 59Fe whole body retention, animals were given a 3 g 59FeCl3 labeled test meal (0.2 microCi). The 2 varieties were tested at 12 and 25 ppm iron as defatted soy flour. Whole fat soy flour of variety 1 (UFV-116) was higher (P0.05) in Ca, K, Mg, phytic acid, and oxalate than variety 2 (OCEPAR-19). No difference was observed among the soybean varieties (P0.05) for femur 65Zn retention, at different levels of zinc. However, whole body retention was lower (P0.05) for UFV-116 than for OCEPAR-19. Femur 65Zn uptake was correlated with the whole body retention; however, whole body retention was more sensitive. Whole body 59Fe retention from UFV-116 was lower (P0.05) than from OCEPAR-19. Zinc and iron bioavailability was lower for UFV-116, possibly due to its higher content of antinutrient factors, especially phytate.

Purpose: Exercise-induced sweat calcium losses have been reported as substantial in male athletes. The first aim of the study was to quantify the increase in 24-h total dermal calcium losses and the net changes in calcium retention in active sportswomen after a 1-h strenuous exercise session. A second aim was to determine the effectiveness of calcium supplementation to offset any calcium loss. Methods: Twenty-six premenopausal sportswomen completed three 8-d intervention phases in a randomized-order, crossover design. The three phases were placebo + no exercise (control), placebo + exercise, and 400 mg of calcium as calcium carbonate (TUMS Ultra) twice daily + exercise. The supervised exercise was 1 h·d-1 cycling at 65-70% of heart rate reserve. A controlled diet of approximately 450 mg·d-1 of calcium and 24-h pooled urine and fecal collections allowed determination of calcium balance on days 5-8 of each phase. Twenty-four-hour dermal collections were made at the end of each phase using a whole-body washdown procedure. Results: Exercise increased (P < 0.05) dermal calcium losses (means ± SD, 92 ± 49 vs 79 ± 31 mg·d-1 in the nonexercise intervention period), which was no longer significant (P = 0.14) when calcium supplementation was provided (83 ± 49 mg·d-1). Higher (P < 0.01) urinary calcium excretion during calcium supplementation is suggestive of higher net calcium absorption. Exercise did not affect urinary calcium excretion indicating lack of compensation for dermal losses. Net calcium retention was positive only during the exercise + calcium supplementation intervention period. Conclusions: Calcium supplementation can correct for negative calcium balance attributable to low calcium dietary intake and additional dermal losses from exercise.

Thus, we investigated the relationship between calcium intake and calcium retention in Asian adolescents to define their calcium requirements based on our nonlinear model. Thirty healthy Chinese bo...

The effect of lignin on calcium absorption was studied in a rat model. Lignin preparations were isolated directly from wheat bran and from kale by two treatments, enzymatic and acidic. Calcium absorption in the presence or absence of isolated wheat bran lignin, isolated kale lignin, commercially available pine lignin, and wheat bran was determined by femur uptake of 45Ca. The fractional calcium absorption of wheat bran was significantly lower than for the control. However, there were no differences in calcium absorption between the various lignin sources and the control without lignin. Thus, lignin is probably not inhibitory to calcium absorption in plant foods.

The purpose of this 3-way crossover study was to identify the effective dose of soy protein isolate enriched with isoflavones for suppressing bone resorption in postmenopausal women using a novel, rapid assessment of antibone resorbing treatments.Thirteen postmenopausal women (or=6 yr since menopause) were predosed with 41Ca iv. After a 200-d baseline period, subjects were given 43 g soy protein/d that contained 0, 97.5, or 135.5 mg total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-d intervention phase was preceded by a 50-d pretreatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four-hour urine samples were collected approximately every 10 d during each phase for 41Ca/Ca analysis by accelerator mass spectrometry.Serum isoflavone levels reflected the amount of isoflavones consumed in a dose-dependent manner. None of the isoflavone levels had a significant effect on biochemical markers of bone turnover, urinary cross-linked N teleopeptides of type I collagen and serum osteocalcin, or bone turnover as assessed by urinary 41Ca/Ca ratios.Soy protein with isoflavone doses of up to 135.5 mg/d did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary 41Ca excretion from prelabeled bone.

National calcium requirements in the United States for boys are based on data from girls. On average, boys develop larger skeletons than do girls, yet it is unknown whether the additional skeletal accretion in boys requires additional dietary calcium intake.The objective was to determine calcium retention in adolescent boys in response to a range of controlled intakes and to compare the intake needed for maximal retention in boys with that needed in adolescent girls studied under the same conditions.Thirty-one boys aged 12-15 y participated in 3-wk metabolic balance studies testing a range (700-2100 mg/d) of calcium intakes in a crossover study design with a 2-wk washout period. Calcium intake was varied by using a beverage fortified with calcium citrate malate. After a 1-wk equilibration period, calcium retention was calculated as dietary calcium intake minus the calcium excreted in the feces and urine over the following 2 wk. The dietary intake at which maximal calcium retention occurred was determined by using a nonlinear regression model. The results in boys were compared with those obtained in 35 adolescent girls previously studied under the same protocol.Maximal calcium retention in boys was achieved at an intake of 1140 mg/d. Calcium retention was higher (by 171 +/- 38 mg/d) in boys than in girls at all calcium intakes studied.The higher calcium retention in boys than in girls was attained through higher net calcium absorption and lower urinary excretion than in girls.

This study assessed the effect of calcium supplementation from dairy vs. calcium carbonate sources on calcium (Ca) retention in overweight and obese adolescent boys and girls. Twenty-three girls (B...

Calcium (Ca)-fortified soymilk has gained popularity in the United States. Tricalcium phosphate (TCP)-fortified soymilk was shown to have a lower Ca bioavailability than cow's milk in men. However, the most popular soymilk in the U.S. is fortified with Ca carbonate (CC) and has not been evaluated. Ca bioavailability from CC-fortified soymilk (CCSM) and TCP-fortified soymilk (TCPSM) was compared with cow's milk in young healthy women using the dual stable isotope technique. In a 3-way crossover design, 20 volunteers (23 +/- 2 y old) consumed 250 mg Ca in cow's milk, CCSM, or TCPSM along with 10 mg 44Ca after an overnight fast. Cow's milk was extrinsically labeled, whereas each fortified soymilk was intrinsically labeled with each chemical salt of 44Ca at the manufacturing facility. Another stable isotope, 43Ca, was injected i.v. 1 h after the complete consumption of cow's milk or soymilk. Fractional Ca absorption was determined from the ratios of 43Ca:42Ca and 44Ca:42Ca by inductively coupled plasma (ICP)-MS in the 24-h urine samples. A mixed linear model (SAS proc mixed) was used to compare the fractional Ca absorption among groups. Fractional Ca absorption in CCSM (0.211 +/- 0.057) did not differ from that of cow's milk (0.217 +/- 0.040), but both were higher (P < 0.05) than that of TCPSM (0.181 +/- 0.039). Our result suggests that calcium absorption is equivalent for CCSM and cow's milk at similar calcium loads.

Blacks develop a higher peak bone mass than whites which is associated with a reduced risk for bone fracture. The physiological basis for the difference in bone mass was investigated by metabolic balance and calcium kinetic studies in adolescent black and white girls. The hypothesis that the greater peak bone mass in blacks compared with whites is due to suppressed bone resorption was tested. Subjects were housed in a supervised environment for 3 wk during which time they consumed a controlled diet and collected all excreta. Subjects were given stable calcium isotopes orally and intravenously after 1 wk adaptation. Blacks have greater calcium retention (mean +/- SD, 11.5 +/- 6.1 vs. 7.3 +/- 4.1 mmol/d, P < 0.05) consistent with greater bone formation rates (49.4 +/- 13.5 vs. 36.5 +/- 13.6 mmol/d, P < 0.05) relative to bone resorption rates (37.4 +/- 13.2 vs. 29.4 +/- 10.9 mmol/d, P = 0.07), increased calcium absorption efficiency (54 +/- 19 vs. 38 +/- 18%, P < 0.05) and decreased urinary calcium (1.15 +/- 0.95 vs. 2.50 +/- 1.35 mmol/d, P < 0.001), compared with whites. The racial differences in calcium retention in adolescence can account for the racial differences in bone mass of adults.

Low bone mass is associated with increased risk of fracture or osteoporosis (Fig. 1). Bone mass increases with age to a peak that, depending on skeletal site, ranges from 16 years to the second or third decade of life. Subsequently, bone mass plateaus and then decreases gradually throughout life at rates of approximately 1%/year. Because bone mass is largely established during adolescence, osteoporosis has been termed a pediatric disease (Chesnut, 1988). One way to focus on improving bone health is to increase our understanding of calcium metabolism in young subjects.

Absorption of calcium from three intrinsically labeled Brussica sp. vegetables was measured in 15 normal women in a three-way randomized design. The test load of calcium was about 83 mg for each source. Fractional calcium absorption from broccoli averaged 0.478 ± 0.089, from bok choy stems, 0.519 ± 0.089, from bok choy leaves, 0.520 ± 0.074, and from kale 0.527 ± 0.091. These differences were both absolutely small and statistically insignificant. Mean absorbability of milk calcium ingested at the same load has been previously shown to be 0.463 ± .095. This value is slightly but significantly lower than the average value for the Brassica sources combined (0.514 ± 0.090). Thus, Brussicu vegetable sources exhibit excellent calcium bioavailability.

To determine whether African-American adolescent girls who were fed a dairy-rich diet for 21 days could adapt to lactose, experiencing an overall improvement in lactose tolerance as well as a decrease in hydrogen gas production.Twenty-one-day dietary intervention study.Seventeen of 21 African-American girls (aged 11 to 15 years) enrolled in a calcium metabolism study chose to participate in the lactose tolerance study. Subjects were screened for any diseases, conditions, or medications that might alter calcium metabolism or colonic fermentation. Subjects were housed in a fraternity on the Purdue University, West Lafayette, Ind, campus, and were supervised 24 hours a day.Subjects consumed a dairy-based diet averaging 1,200 mg calcium and 33 g lactose per day for 21 days. Lactose digestion was assessed by an 8-hour breath hydrogen test on days 1 and 21, and symptoms of intolerance (abdominal pain, bloating, flatulence, and diarrhea) were evaluated hourly on a ranked scale during the breath hydrogen tests and once each evening during the 21-day feeding period.A comparison of breath hydrogen production and gastrointestinal symptoms at the beginning and end of the study.The Wilcoxon signed ranks test was used to compare the area under the curve for the 2 breath hydrogen tests. Spearman's p test for trend was used to determine whether there was a change in symptoms. All statistical analyses were 2-tailed and significance was set at P = .05.Fourteen of the 17 subjects had lactose maldigestion. Breath hydrogen excretion decreased significantly (P.03) from the beginning (148.3 +/- 27.0 ppm x hours) to the end (100.7 +/- 19.3 ppm x hours) of the 21-day period. Gastrointestinal symptoms were negligible during both the breath hydrogen tests as were symptoms during the 21-day period.The diet was well tolerated by the subjects. Furthermore, the decrease in breath hydrogen suggests colonic adaptation to the high-lactose diet. The results indicate that lactose maldigestion should not be a restricting factor in developing adequate calcium diets for this population. The existence of lactose maldigestion does not result in lactose intolerance in this population when it is fed a dairy-rich diet.

Calcium salts, such as calcium carbonate and calcium acetate, are the principal compounds used as phosphate binders in patients with chronic renal failure. The dose required is three to six times the normal requirement for calcium. Use of these large doses of calcium salts in the diet can result in hypercalcemia. Other compounds have been investigated as phosphate binders with varying degrees of success. Synthetic ferrihydrite (5Fe(2)O(3).9H(2)O) has a high adsorptive capacity for phosphate and may be an effective phosphate binder. The phosphate-binding capacity of ferrihydrite was compared with that of calcium acetate in 250-g male Sprague Dawley rats. After an overnight fast, rats (n = 5 per group) were gavaged with an American Institute of Nutrition (AIN) 76 formula containing one third the daily phosphorus intake labeled with phosphorus-32 ((32)P). Either two levels of calcium acetate, representing three (1/2X) or six (1X) times the usual calcium intake for one third of the day, or equivalent amounts of ferrihydrite were added to the diet. An additional group received two times (2X) the larger dose, and a sixth control group received no binder in the diet. Phosphorus absorption curves were determined from (32)P appearance in the serum. The 1/2X dose of ferrihydrite reduced (32)P by approximately one half, and the 2X dose nearly completely suppressed (32)P absorption, similar to the 1X dose of calcium acetate. The advantage of using a ferrihydrite binder would be to avoid the hypercalcemia resulting from the use of high-dose calcium salts. An added advantage may result from the small amounts of iron absorbed in these chronically iron-deficient patients.

The quantification of biochemical markers of bone formation and resorption with kinetic measures of bone turnover is an essential step in their validation. Some biochemical markers have been validated by quantification against formation and resorption rates measured by calcium kinetics in adults with bone disease. However, none has been validated in healthy individuals who are undergoing skeletal growth and bone consolidation. Therefore, we have measured biochemical markers of bone formation (serum osteocalcin [OC], bone-specific alkaline phosphatase [BAP], and total alkaline phosphatase [ALP]) and resorption (serum tartrate resistant acid phosphatase [TRAP], urinary cross-linked N teleopeptides of type I collagen/creatinine [NTx/Cr], and hydroxyproline/creatinine [OHP/Cr]) in healthy females aged 11-32 years (n = 31) after an overnight fast to determine their relationship with bone formation (Vo+) and bone resorption (Vo-) as measured by calcium kinetics and balance. All biochemical markers were highly intercorrelated (r > 0.6, p < 0.001) as were Vo+ and Vo- (r = 0.91, p < 0.001). Highly significant correlations were present between bone formation measured by calcium kinetics (Vo+) and serum levels of bone biochemical markers (OC, r = 0.82, p = 0.001; ALP, r = 0.92, p = 0.001; and BAP, r = 0.90, p = 0.001) and between bone resorption measured by calcium kinetics (Vo-) and fasting serum levels and urine creatinine ratios of biochemical markers (TRAP, r = 0.77, p < 0.001; OHP/Cr, r = 0.79, p < 0.001; and NTx/Cr, r = 0.70, p < 0.001). Thus, biochemical markers of bone formation and resorption can be used to predict calcium kinetic rates during skeletal growth and the early years of formation of peak bone mass, ages at which strategies to build peak bone mass are important. Biochemical markers of formation and resorption are equally useful in predicting either the bone formation rate or the resorption rate.

Because of the lack of a suitable isotope and a sensitive technique of analysis, aluminum has been studied indirectly using analogs such as 67Ga (t1/2 = 78 hr). Recently, with the development of accelerator mass spectrometry (AMS), it has become possible to use the artificially produced radionuclide of aluminum, aluminum 26 (26AI), (t1/2 = 7.16 x 10(5) years). AMS is used for measuring long-lived and stable isotopes with the sensitivity of an attomole (10(-17) mol). To study aluminum metabolism, 26AlCl3 was administered to rats intraperitoneally (ip) by injection and orally by gavage (n = 3/group). Blood was collected periodically. On Day 8 following perfusion, blood, liver, kidney, femur, brain, and spleen were collected and analyzed for 26AI. Of all the tissues studied, 26AI accumulation was greatest in the bone. 26AI accumulated in tissues as: bone > spleen > kidney approximately liver > brain, but absorption was low (0.97% of dose). AMS offers great potential in AI research as it is the only technique available for tracer aluminum study.

Achievement of maximal calcium retention during adolescence may influence the magnitude of peak bone mass and subsequently lower the risk of osteoporosis. Calcium retention is generally considered to reach a plateau at a certain calcium intake. To test this hypothesis, calcium balance was measured in 35 females with a mean (+/-SD) age of 12.7 +/- 1.2 y (range: 12-15 y) who consumed from 841 +/- 153 to 2173 +/- 149 mg Ca/d. Subjects ate a basal diet that included a fortified beverage containing different amounts of calcium citrate malate. Twenty-one subjects were studied at two dietary calcium intakes with use of a crossover design. Results from a previous study in 14 subjects who were studied at only one calcium intake were included in the data analysis. Calcium retention was modeled as a nonlinear function of calcium intake that included a parameter representing mean maximal retention. Mean maximal calcium retention was 473 mg/d (95% CI: 245, 701 mg Ca/d). At higher postmenarcheal ages, maximal calcium retention was lower but the intake required to achieve this was not affected. Calcium intake explained 79% and 6%, respectively, of the variation in fecal and urinary calcium excretion. Intake of 1200 mg Ca/d, the recommended dietary allowance for calcium published in 1989, resulted in a mean calcium retention that was 57% of the maximal value (95% CI: 25%, 89%). Intake of 1300 mg Ca/d was the smallest intake that allowed some adolescent females to achieve 100% of maximal calcium retention (95% CI: 26%, 100%). These data support the idea that calcium retention plateaus at a certain calcium intake although it continues to increase at intakes > 2 g/d.

Glutaraldehyde treatment of collagen biomaterials promotes calcification, poor host-tissue incorporation, and ultimately mechanical failure of bioprotheses. Porcine small-intestinal submucosa (SIS) is a biomaterial which has been investigated for several applications including arterial and venous grafts and repair of tendon, ligament, body wall, and urinary bladder defects. The calcification potential of peracetic acid (PAA)-sterilized SIS was studied. Four test samples, (1) native (cleaned, untreated) SIS, (2) SIS sterilized with 0.1% PAA, (3) SIS treated with 0.25% glutaraldehyde for 20 min, and (4) commercially available glutaraldehyde-preserved porcine bioprosthetic heart valve cusp segments (GPV), were each implanted subcutaneously in each of 24 weanling rats. Six rats were euthanatized at 1, 2, 4, and 8 weeks. Evaluation of calcium concentration by atomic absorption spectroscopy and extent of mineralization and fibrosis by light microscopy were performed. Atomic absorption revealed no calcification in native or peracetic acid-treated SIS at any time point compared with preimplant calcium concentration. Statistically significant (P0.0001) calcification occurred in glutaraldehyde-treated materials (SIS and GPV) at each evaluation as compared to native and peracetic acid-treated samples. Histopathology indicated native and peracetic acid-treated SIS showed no implant mineralization (P0.0001) and little peri-implant fibrosis (P0.0001). Results suggested that native and peracetic acid-treated SIS have a low calcification potential and further study of this biomaterial is warranted.

Stable isotopes were used to compare calcium fractional absorption from intrinsically and extrinsically labeled bovine milk as well as intrinsically labeled dairy product and cheese analogue. Healthy Caucasian women were fed a controlled diet for 4 d during the follicular phase of their menstrual cycle. With breakfast on the third day, participants ingested milk containing 44 Ca (intrinsic) and 42 CaCl 2 (extrinsic) or dairy products containing 44 Ca. Total feces were collected for 2 d prior to and 10 d after isotope ingestion. Polyethylene glycol was administered to monitor completeness of fecal collections. Total calcium was determined by atomic absorption spectrophotometry, and isotopic abundance was determined by high resolution fast atom bombardment mass spectrometry. Fractional absorption was determined as the difference between the administered isotopic dose and the quantity of 44 Ca or 42 Ca excreted in feces. The fractional absorption of calcium from milk was not affected by the method of labeling, lactose content, fermentation or the chemical form of calcium in dairy products or cheese analogue.

Calcium absorption from fumarate salts (calcium fumarate and calcium malate fumarate), which have recently been considered for use as sources for food and beverage enrichment, was compared to that from calcium citrate malate, calcium citrate, and calcium carbonate. Salts were instrinsically labeled with 45Ca and orally administered to Sprague-Dawley rats. Fractional absorption of calcium from each salt was determined using the femur uptake model. Fractional absorption from the five salts (0.30-0.27) was not significantly different (p > 0.05). Thus, when measured in the rat model, calcium from calcium fumarate and calcium malate fumarate is absorbed equally well as compared to other salts, which are common calcium sources in many foods, beverages, and supplements.

Forty-seven previously sedentary women participating in a 12-wk moderate aerobic-exercise program were randomly assigned to one of four dietary groups: 50-mg/d iron supplement and a low food-iron diet (50 FE + EX), 10-mg/d iron supplement and a low food-iron diet (10 FE + EX), placebo and unrestricted diet (P + EX), and meat supplement and high food-iron diet (M + EX). A sedentary control group (n = 13) received no dietary interventions. Hematocrit, total iron-binding capacity, and hemoglobin, serum iron, serum ferritin, and serum albumin concentrations were measured every 4 wk. Hemoglobin values decreased at the end of 4 wk in all exercising groups compared with the control group. Iron status in the 50 FE + EX and M + EX groups improved after week 4 as indicated by an increase in serum ferritin, serum iron, and hemoglobin concentrations, and a decline in total iron-binding capacity. Thus, short-term, moderate aerobic exercise resulted in compromised iron status that was offset to varying degrees by ingesting iron or meat supplements. However, meat supplements were more effective in protecting hemoglobin and ferritin status than were iron supplements.

Fractional absorption of calcium from bread made either from intrinsically or extrinsically labeled whole-wheat flour was compared in 11 healthy adult women. The intrinsic label was provided by 45Ca injected individually into stems of wheat plants during growth. The extrinsic tag was introduced by adding 45Ca to unlabeled flour via the water used in dough making. The two labeled breads were tested in a randomized crossover design using a standardized breakfast administered after an overnight fast. Approximately 80 g labeled bread was consumed by each subject, providing a total calcium load of 13.3 mg. Fractional absorption from the intrinsically labeled bread averaged 0.812 +/- 0.130 (mean +/- SE) and from the extrinsically labeled bread 0.792 +/- 0.113. The mean difference, within subject, was only 0.025 +/- 0.016 and was not significantly different from zero. Extrinsic labeling of the calcium of whole-wheat flour results in a degree of labeling homogeneity equivalent to that of intrinsic labeling, at least for a leavened bread product.

Fractional calcium absorption from wheat products and the influence of co-ingested wheat products on calcium absorption from milk were measured in a series of randomized crossover studies in healthy adult women. The wheat had been intrinsically labeled with 45Ca during growth. In the first study, fractional calcium absorption from leavened whole-wheat bread averaged 0.817 +/- 0.124. By comparison, absorption from milk, ingested at a comparable load in the same women, averaged only 0.589 +/- 0.111. When labeled bread was co-ingested with milk, at the same aggregate load as for bread alone, bread calcium absorption fell to 0.748 +/- 0.103 (P less than 0.05). In a second study, calcium absorption from an extruded cereal prepared from intrinsically labeled wheat bran was compared with milk. Calcium absorption from the cereal (0.223 +/- 0.046) was significantly less than from milk (0.375 +/- 0.072) (P less than 0.001). When the two were co-fed at the same total load, milk calcium absorption fell to 0.258 +/- 0.055 (P less than 0.001). In a third study, the effect of phytate hydrolysis through yeast fermentation and of Maillard browning on calcium absorption was investigated using leavened bread and underbaked and overbaked cookies, each made with intrinsically labeled wheat flour. Calcium absorption from cookies was not affected by the extent of browning and averaged 0.652 +/- 0.087. However, calcium absorption from bread in these same women averaged 0.703 +/- 0.108. This was significantly more than from the cookies (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium absorption from salts and foods intrinsically labeled with 45Ca was determined in the rat model. Calcium bioavailability was nearly 10 times greater for low oxalate kale, CaCO3 and CaCl2 than from CaC2O4 (calcium oxalate) and spinach (high in oxalates). Extrinsic and intrinsic labeling techniques gave a similar assessment of calcium bioavailability from kale but not from spinach.

Calcium endogenous to bovine milk was biosyntheticallylabeled by intravenous injection of calcium highly enriched in 44 Ca to a single lactating dairy cow. Approximately 63% of a 4 g dose was recovered in the milk in 56.5 h. The milk was homogenized, pasteurized and then stored at −70°C after processing. A 300% enrichment of 44 Ca in the first postdose milking was sufficient for use in human feeding studies currently underway.

This study investigated the effects of vitamin A excess on hepatic galactosyltransferase (EC 2.4.1.13) activity in livers of rats achieved either by feeding of high levels of retinyl palmitate for 16 wk or gavaging with retinol in olive oil for 3 d. Both hypervitaminotic conditions were characterized by hepatic lipid accumulation. Golgi apparatus fractions were isolated and purity of the fractions was monitored by marker-enzyme analyses and electron microscopy. The quality of the fractions isolated from livers of rats receiving vitamin A excess was not different from that of fractions from control rats. An increase in fat-storing cells in liver, observed in vitamin A excess, coincided with the presence of a floating lipid layer present during isolation of the Golgi apparatus. Galactosyltransferase specific activity (with ovomucoid as acceptor) of Golgi apparatus of rats fed excess vitamin A was 27% of control with chronic feeding and 59% of control with administration by gavage. Activity of another luminally oriented protein, uridine 5'-diphosphate phosphatase, was increased under both in vivo regimens. Vitamin A content of Golgi apparatus, as determined by high performance liquid chromatography, correlated negatively with galactosyltransferase activity after both chronic and acute administration of excess vitamin A.

The acute and chronic effects of whey proteins on calcium metabolism and bone were evaluated. In acute studies, 8-week-old male rats were gavaged with 50 mg whey protein concentrate (WPC) and 25 mg calcium. 45Ca was administered intravenously or orally. Kinetic studies were performed, and femurs were harvested. Four of seven WPCs significantly increased femur uptake of 45Ca compared with controls. One WPC at 50 mg enhanced calcium absorption over a range of calcium Intakes from 35.1 ± 9.4% to 42.4 ± 14.0% (P < 0.01). Three of the most effective WPCs were tested further in a chronic feeding study. One hundred 3-week-old rats were randomly divided into four adequate dietary calcium (ADC; 0.4% Ca) groups (control of 20% casein and three WPC groups with 1% substitution of casein with each of three WPCs) and two low calcium (LC; 0.2% Ca) groups (control of 20% casein and one WPC group with 1% substitution of casein with one WPC). After 8 weeks, there was no effect of WPCs on femur uptake of 45Ca among ADC groups and there was no effect of WPCs on calcium retention, femur breaking force, femur bone mineral density, or total femur calcium at either dietary calcium intake. However, whole body bone mineral content (BMC) was significantly higher (P < 0.05) in the three whey protein concentrate ADC groups compared with the ADC control group. Total BMC at the proximal tibia in whey protein ADC groups was increased, as shown by peripheral quantitative computed tomography. Our results indicate that the acute calcium absorption–enhancing effect of whey proteins did not persist through long-term feeding in rats. However, the initial enhancement of calcium absorption by whey protein was sufficient to Increase BMC.