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The accuracy of portion size estimates is critical in dietary assessment. The objectives of this study were to determine the magnitude and direction of error in estimating food amounts using computer-based portion anchors; to compare errors between use of computer- and poster-displayed anchors; and to assess level of accuracy that can reasonably be expected for different food types. A total of 101 subjects estimated amounts of food items (five solid, four amorphous, three liquid) using computer-based portion anchors. Half of the subjects also estimated five of the foods using digital photographs printed onto a poster. Two modes of testing were conducted: real time, in which foods were displayed near the computer or poster, and short-term recall, in which food was consumed and then estimated. Overall error (mean± se ) in real time was 4.8%±1.8%; by food type, solid was 8.3%±2.3%, amorphous was −10%±2.7%, and liquid was 19%±5%. However, group mean values could mask true errors. This research showed that even within food type, variables including amount served and its closeness to anchor size affected accuracy of estimates. For each food, amount served correlated inversely with magnitude of error. The findings provide insight into sources of error in portion estimation, and factors to consider in setting reasonable levels of accuracy.

BACKGROUND Information is lacking regarding the effects of beta-carotene supplementation, early lactation, or both on circulating carotenoid concentrations and T lymphocyte proliferation. OBJECTIVES This study investigated the effects of short-term beta-carotene supplementation (30 mg/d for 28 d) during early lactation (days 4-32 postpartum) on circulating carotenoid concentrations and on the T lymphocyte proliferative response to phytohemagglutinin. DESIGN Subjects aged 19-39 y were paired [lactating (4 d postpartum) and nonlactating (never pregnant, healthy women)] and randomly assigned to receive either beta-carotene or a placebo. During the study, subjects provided eight 24-h food records for analysis with the NUTRITIONIST IV and US Department of Agriculture carotenoid databases. Nonfasting blood samples were collected at baseline and at 28 d. Plasma analysis included quantification of alpha-carotene, beta-carotene, lutein, lycopene, retinol, and alpha-tocopherol, complete differential blood cell counts, and lymphocyte proliferative activity. RESULTS beta-Carotene supplementation increased beta-carotene (P < 0.001) and alpha-carotene (P < 0.05) concentrations but did not affect lycopene concentrations significantly. Supplemented women showed significant decreases in plasma lutein (P < 0.03), as did lactating subjects (P < 0.02). Neither lactation nor beta-carotene supplementation affected the T lymphocyte proliferative response to phytohemagglutinin. CONCLUSIONS Our results suggest that beta-carotene supplementation as well as some events related to parturition, initiation of lactation, or both alter circulating concentrations of lutein. beta-Carotene supplementation does not enhance T lymphocyte immune competence in healthy women.

A method for the measurement of calcium isotopes (42Ca, 43Ca, and 44Ca) using quadrupole inductively coupled plasma mass spectrometry (ICP-MS) is described. Interferences from polyatomic ions such as 12C16O2+ and 40ArH2+ at the calcium masses are greatly minimized by operating the ICP-MS in the cool plasma mode. Relative standard deviations (RSD) for the 42Ca∶43Ca and 44Ca∶43Ca ratios were found to be about 0.25%. Sample preparation involved using ammonium oxalate at a pH of 8 to separate calcium from samples such as serum, urine, feces, and breast milk. The isotope ratio measurements were used to determine fractional absorption of calcium by a lactating woman after intravenous administration of 42Ca and ingestion of 44Ca.

To determine the fate and distribution of chromium during lactation, six lactating women (25-38 y old) were given three doses of the tracer 53Cr (7.55 micromol/d, or 400 microg/d) on days 1, 2, and 3 of the study. Diet records, blood samples taken while subjects were fasting, and 24-h composite milk and urine samples were collected from day 0 to day 6. Fasting blood samples, morning milk samples, and 24-h urine samples were also collected on days 8, 10, 15, 30, 60, and 90. 53Cr and natural and total chromium concentrations in biological fluids were measured with gas chromatography-mass spectrometry and total urinary chromium was measured with atomic-absorption spectrometry. 53Cr was detectable in serum 2 h after dosing and continued to be detected from day 30 to day 60. Changes in total serum chromium concentration in response to the oral dose suggested that chromium concentrations in blood were not tightly regulated. 53Cr was not detected in breast milk and no significant changes in natural chromium concentration in milk were observed in response to the oral doses, suggesting that breast-milk chromium concentrations are independent of intake. The estimated chromium intake of exclusively breast-fed infants was 2.5 nmol/d (0.13 microg/d), below the lower end of the range of estimated safe and adequate daily dietary intakes (10-40 microg/d) for infants 0-6 mo of age. The baseline chromium concentration in urine and the minimum 53Cr absorption in lactating women were comparable with values for nonpregnant, nonlactating subjects. Chromium losses in breast milk do not appear to be compensated for via increased absorption or decreased excretion.

Both exercise and chromium exert beneficial effects on insulin function. The mechanism by which exercise improves insulin response may involve an alteration in Cr metabolism. To determine the effects of acute and chronic resistive exercise on urinary Cr losses, we measured the effects of acute resistive exercise and 16 wk of resistive exercise training on urinary Cr losses of 10 men 53-63 y of age. Subjects consumed diets in compliance with the American Heart Association Phase I diet with a Cr content of 30 +/- 4 microg/d. Sixteen weeks of resistive exercise training led to approximately 40% increases in upper and lower body strength, increases in fat-free mass and decreases in the percentage of body fat. An enriched stable isotope of Cr, 53Cr, was employed to differentiate the exogenously administered Cr from the native endogenous Cr. Both acute and chronic resistive exercise increased 53Cr losses. These data demonstrate that the improvements in body composition due to resistive exercise are associated with increased urinary Cr losses that are consistent with increased absorption.

Postpartum lactating (n = 12) and nonlactating (n = 11) women and never pregnant women (n = 14) collected urine samples and diet records 2 d each month for 6 mo to determine whether postpartum women conserved urinary calcium, magnesium, or zinc. Mean daily excretions were analyzed by repeated-measures analysis of variance and covariance to assess group and time effects. Lactating women excreted less urinary calcium (1-6 mo) than never pregnant (n = 8) and nonlactating (n = 4) women who did not use oral contraceptives (P0.01); however, excretion rose (P0.05) by 3 mo postpartum. In the nonlactating and never pregnant groups, women using oral contraceptives excreted less urinary calcium than the other women (P0.01). Lactating women excreted less urinary zinc (1-6 mo) than did control and non-lactating women (P0.01). Mechanisms may possibly be operating during lactation that depress urinary calcium foror = 2 mo and urinary zincor = 6 mo postpartum.

This study was undertaken to determine whether lactating women consuming a low-magnesium diet compensate for magnesium secreted into breast milk by decreasing urinary magnesium losses. Six lactating (L) women, six nonlactating (NL) women (75 +/- 5 and 61 +/- 5 d postpartum, respectively), and seven never-pregnant (NP) women were studied while consuming a constant magnesium intake of 8.97 +/- 0.01 mmol/d for 20 d. After a 5-d stabilization period on the controlled diet, 24-h urine and fecal samples were collected for the next 15 d. The L women excreted significantly less (P < 0.01) urinary magnesium (2.10 +/- 0.35 mmol/d) than the NP women (3.45 +/- 0.37 mmol/d). No significant differences were detected in mean apparent magnesium absorption among the three groups of women, because of large individual variations of fecal magnesium and small sample size. L women apparently compensated for magnesium losses in breast milk (1.04 +/- 0.06 mmol/d) by reducing urinary magnesium losses (1.38 mmol/d) when consuming 8.97 mmol Mg/d.

A method is described for the determination of chromium and its enriched stable isotopes in human urine by isotope dilution mass spectrometry. A volatile chelate is formed with trifluoroacetylacetone (TFA) and the fragment ions corresponding to Cr(TFA) 2 + in the 350-360 m/z region are monitored. The chelate is thermally stable and exhibits no memory effect when isotope ratios change. The detection limit for the method is 0.03 ng of Cr/g, and the accuracy is verified by certified reference materials and by an independent method

This study examined the effects of pregnancy and glucose loading on plasma and erythrocyte (RBC) magnesium (Mg) concentrations. In a completely randomized design with repeated measures, 15 nonpregnant, 15 early pregnant (13-17 weeks) and 15 late pregnant (28-34 weeks) women ingested 100 g glucose. Blood was collected at 0, 30, 60, 120 and 180 minutes to evaluate changes in Mg levels. Fasting plasma Mg concentrations decreased slightly but not significantly as gestational age of the groups increased. Fasting RBC Mg concentrations were significantly higher (p less than 0.05) in late pregnant women compared with early pregnant and nonpregnant women. Plasma Mg responses to a glucose challenge in nonpregnant women exhibited a curvilinear pattern whereas responses in pregnant women appeared unaffected by the glucose challenge. RBC Mg concentrations for nonpregnant and early pregnant women failed to respond to the glucose challenge whereas it decreased in a linear pattern during late pregnancy. The diabetogenic effect of late pregnancy appears to affect RBC Mg. This redistribution of Mg during late pregnancy could suggest a possible role for RBC as a Mg pool.

A method is described for using isotope dilution to determine both the amount of natural zinc and enriched isotopes of zinc in biological samples. Isotope dilution inductively coupled plasma mass spectrometry offers a way to quantify not only the natural zinc found in a sample but also the enriched isotope tracers of zinc. Accurate values for the enriched isotopes and natural zinc are obtained by adjusting the mass count rate data for measurable instrumental biases. Analytical interferences from the matrix are avoided by extracting the zinc from the sample matrix using diethylammonium diethyldithiocarbamate. The extraction technique separates the zinc from elements which form interfering molecular ions at the same nominal masses as the zinc isotopes. Accuracy of the method is verified using standard reference materials. The detection limit is 0.06 μg Zn per sample. Precision of the abundance ratios range from 0.3–0.8% R.S.D. for natural zinc concentrations of about 200–600 μ g−1. The accuracy and precision of the measurements make it possible to follow enriched isotopic tracers of zinc in biological samples in metabolic tracer studies.

Decisions about bylines, although seemingly straightforward, can "breed ill-will," "wreck friendships," and "even damage careers" if decisions are not in accord with professional guidelines and common sense. Editors have attempted to promote responsible authorship by creating Uniform Requirements. According to the International Committee of Medical Journal Editors, each author must have made a substantial contribution to all 3 of the following conditions to qualify for authorship: conceiving and designing the work represented by the article or analyzing and interpreting data; drafting the article or revising it critically for important intellectual content; and giving final approval of the version to be published. Despite these guidelines, bylines continue to include grafters and guests. Researchers believe guidelines for authorship are necessary but suggest the existing Uniform Requirements may be overly restrictive and easily misinterpreted. Editors will need to work with researchers to reach consensus on realistic and appropriate guidelines for authorship. J Am Diet Assoc. 1999;99:77-79 .

Few data are available to establish recommendations for trace element supplementation during critical illness. This study quantified the loss of several elements and assessed the adequacy of manganese and selenium in parenteral nutrition (PN).Men with traumatic injuries were grouped by renal status: adequate (POLY; n = 6), acute failure with continuous venovenous hemofiltration (CVVH; n = 2), or continuous venovenous hemodiafiltration (CVVHD; n = 4). PN supplied 300 microg/d manganese and 60 microg/d selenium. Urine and effluent (from artificial kidneys) were collected for 3 days and analyzed for boron, manganese, nickel, and silicon using inductively coupled plasma atomic emission spectrometry, and for selenium using atomic absorption spectrometry.POLY manganese and selenium excretion averaged (standard deviation [SD]) 7.9 (3.3) microg/d and 103.5 (22.4) microg/d, respectively. All elements except selenium were detected in dialysate (prior to use). CVVHD effluent contained 3.5 and 7.3 times more manganese and nickel than CVVH ultrafiltrate, respectively. Loss of manganese averaged 2.6%, 21%, and 73% of PN amounts for POLY, CVVH, and CVVHD groups, respectively.Minimal loss of manganese compared with the amount in PN suggests that excessive amounts are retained. POLY patients excreted more selenium than was in PN, indicating negative balance. POLY losses of boron and silicon were less than that published for healthy adults, reflecting less than typical intake, whereas loss during CVVH was in the normal reference range, possibly because of added intake from boron contamination of replacement fluids. All patients lost more nickel than amounts published for healthy adults.Current guidelines of 60-100 microg/d of parenteral manganese may be excessive for trauma patients. The uptake of manganese and nickel from contaminants in CVVHD dialysate should be investigated.

Two important factors that determine zinc nutriture are the amount of zinc provided by the food supply and the zinc content of the foods individuals eat. The amount of zinc provided by the U.S. food supply has varied between 11 and 13 mg/day/person since the beginning of the century. Currently, it is estimated that the U.S. food supply provides 12.3 mg zinc per person per day. Data from the Food and Drug Administration’s Total Diet Study and the U.S. Department of Agriculture’s Nationwide Food Consumption Survey of Individuals and year-long BeltsviIle diet study indicate that adult males select diets that contain 90% or more of the 1989 Recommended Dietary Allowance (RDA) for zinc, whereas women select diets that have less than 81% of the RDA for zinc. Zinc densities of the diets for men and women were similar, which suggests that the difference in total zinc intake is attributable to a difference in energy consumption. Consumption patterns that meet the RDA for zinc can be compatible with the recent National Academy of Sciences diet and health recommendations. The dietetic practitioner should encourage consumption patterns that include using zinc-rich foods in the form of poultry and lean meats and low-fat or nonfat dairy products; using grain products and legumes, particularly whole grains, which can make an important contribution to total zinc intake; and increasing physical activity to a moderately active level to increase energy and zinc intake.

Forty lactating women were randomly as- signed to four treatment groups. Beginning at l-d postpartum the women in each group received a daily vitamin-mineral sup- plement for 9 mo. The treatments differed only in the amount ofvitamin B-6 (0.5 or 4.0 mg pyridoxinc) and zinc (0 or 25 mg) included in the supplements. The 4.0-mg pyridoxinc supple- ments significantly increased plasma total vitamin B-6, plasma pyridoxal phosphate (PLP), and milk total vitamin B-6, thus showing that maternal intake exerts a significant effect on vita- mm B-6 concentration in milk. There was no effect of vitamin B-6 intake on plasma, erythrocyte, or milk zinc concentration. The 25-mg zinc supplement also had no effect on plasma, erythrocyte, or milk zinc concentration, suggesting that mater- nal zinc intake is not a major regulator of milk zinc concentration. Am J Clin Nutr l990;52: 135-41.

This study determined whether a single 60-mg dose of ferrous sulfate interferes with fractional zinc absorption (FZA) at 7-9 wk of lactation. In a crossover design, 5 exclusively breast-feeding women were given either a single 60-mg iron supplement or no supplement. FZA was measured by analyzing zinc stable isotope tracers ((70)Zn and (67)Zn) in urine samples collected for 7 d after isotope dosing. A 0.7-micromol intravenous (IV) infusion of (70)Zn as ZnCl(2) in saline was followed by a 0.03-mmol oral dose of (67)Zn as ZnCl(2) given with a standardized meal. After a 7-d wash-out period, the supplement given was reversed and a second FZA measurement was taken. FZA was calculated from isotopic enrichments in urine measured by inductively coupled plasma mass spectrometry. Hemoglobin, plasma ferritin and transferrin receptor, and plasma 5'-nucleotidase, plasma zinc and erythrocyte zinc did not differ before the two measurements of zinc absorption. When women were given a single iron supplement, FZA was significantly lower, 21.7 +/- 1.7% compared with 26.9 +/- 2.6% when no supplement was given (P = 0.032). A single 60-mg iron dose significantly decreases FZA during early lactation.

BACKGROUND Information is lacking regarding normal changes in milk carotenoid concentrations in healthy, well-nourished women during the first month of lactation. OBJECTIVES This study investigated milk carotenoid concentrations during days 4-32 postpartum and assessed the effects of maternal beta-carotene supplementation. DESIGN Subjects (n = 21; aged 19-39 y) were randomly assigned to receive beta-carotene (30 mg/d) or placebo from days 4 to 32 postpartum. Each subject provided 8 diet records and 8 milk samples during the study. Diet records were analyzed for energy, macronutrients, vitamins A and E, and carotenoids. Milk samples were analyzed with HPLC for concentrations of carotenoids, retinol, and alpha-tocopherol. Data were analyzed by using repeated-measures analysis and orthogonal contrasts. RESULTS No significant differences in average dietary intakes, body mass index, age, or parity were found between groups at baseline or after supplementation. Milk carotenoid concentrations decreased over time (P < 0.01), as did retinol and alpha-tocopherol concentrations (P < 0.003). Concentrations of most carotenoids decreased to those reported for mature milk by day 32 postpartum. Milk lutein concentrations remained elevated throughout the study compared with values reported for mature milk, whereas plasma lutein concentrations decreased significantly over time. beta-carotene supplementation did not significantly change the milk concentrations of beta-carotene, the other carotenoids, retinol, or alpha-tocopherol. CONCLUSIONS The lack of increase in milk beta-carotene despite supplementation suggests that transitional milk may be already nearly saturated with beta-carotene. The elevated milk lutein concentration and simultaneous decrease in plasma lutein suggest that lutein metabolism may be altered during early lactation.

Whether standard nutrition support is sufficient to compensate for mineral loss during continuous renal replacement therapy (CRRT) is not known.Adult men with traumatic injuries were recruited; one-half of recruits required CRRT for acute renal failure. All urine and effluent (from CRRT) were collected for 72 hours. Urine, effluent, and dialysate were analyzed for magnesium, calcium, and zinc using atomic absorption spectrometry. Urea nitrogen in blood, urine, and effluent were determined by measuring conductivity changes after the addition of urease. Blood was analyzed for magnesium and calcium as part of routine care. Intake was calculated from orders and intake records.Patients receiving CRRT (n = 6) lost 23.9+/-3.1 mmol/d (mean +/- SEM) of magnesium and 69.8+/-2.7 mmol/d of calcium compared with 10.2+/-1.2 mmol/d and 2.9+/-2.5 mmol/d, respectively, lost in patients not in acute renal failure (n = 6; p.01). Zinc intake was significantly greater than loss in both groups (p.03). Urea nitrogen excretion did not differ between groups. Serum magnesium was 0.75+/-0.04 mmol/L for CRRT patients, significantly lower than the 0.90+/-0.03 mmol/L for control patients (p.01). Total blood calcium was below normal in both groups; ionized calcium was below normal in CRRT patients.CRRT caused significant loss of magnesium and calcium, necessitating administration of more magnesium and calcium than was provided in standard parenteral nutrition formulas. However, additional zinc was not required. CRRT removed amounts of urea nitrogen similar to amounts removed by normally functioning kidneys.

Determining the fractional absorption (FA) of calcium using the incorporation into urine of stable isotopes given intravenously (IV) and orally has become a routine procedure. We investigated the FA of calcium in two groups of (2-3 mo) postpartum women lactating (LACT) (n = 6) and nonlactating (PPNL) (n = 6), and in never pregnant (NP) women (n = 7). The women consumed a controlled diet containing 30-33 mmol/d calcium (Ca) for 21 d. On d 7 of the controlled diet, the women received 0.05 mmol of 42Ca IV and 0.25 mmol 44Ca orally in milk. Urine samples (24-h) were collected for the next 14 d and morning blood samples were collected from fasting subjects before dosing and at 24 and 48 h after receiving the isotopes. Milk samples from the LACT women were collected from each feeding beginning 24 h before to 72 h after dosing. There were no significant differences in the FA of calcium as measured by stable isotope incorporation into urine (23.8 +/- 2.9%), serum (24.0 +/- 3.4%) or milk (23.6 +/- 3.6%) of LACT women. The fractional calcium absorption measured in urine of the postpartum women (LACT and PPNL, 23.8 +/- 2.9% and 25.0 +/- 3.3%, respectively) did not differ but was greater (P < 0.028) than that of the NP women (17.3 +/- 1.3%). The postpartum LACT and PPNL women had a reduced urinary excretion of calcium (P < 0.01) compared with the NP women. There was a significantly greater incorporation (P < 0.001) by LACT women of the oral isotope dose into milk than into urine. Calcium FA can be determined from incorporation of stable isotopes into breast milk and serum as well as urine.

Background: Iron deficiency, a pervasive problem among low-income women of childbearing age, threatens maternal health and pregnancy outcomes. The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) was designed to alleviate health problems and provides supplemental nutritious foods, nutrition education, and health care referrals. Objectives: The aim of this study was to examine the benefits associated with participation in WIC in terms of biochemical tests of postpartum iron status in nonlactating women. Design: WIC participants (n = 57) and eligible nonparticipants (n = 53), matched by race and age, were followed bimonthly over 6 mo postpartum. Finger stick blood samples (500 μL) were collected for measurement of plasma ferritin, transferrin receptor (TfR), and hemoglobin (Hb). Results: The mean (±SE) Hb concentration of participants exceeded that of nonparticipants from months 2 through 6. At 6 mo, the mean Hb concentration of participants was significantly higher than that of nonparticipants (8.01 ± 0.12 and 7.63 ± 0.12 mmol/L, respectively; P < 0.05) and the prevalence of anemia was significantly lower (17% and 51%, respectively; P < 0.05). TfR and ferritin concentrations (consistently within the reference ranges) and dietary iron intakes did not differ significantly between participants and nonparticipants and were not correlated with Hb concentrations. Conclusions: Our results suggest that WIC participants were significantly less likely to become anemic if uninterrupted postpartum participation lasted for 6 mo. The lack of correlation among iron status indicators suggests that the lower mean Hb concentration in nonparticipants at 6 mo may not have been related to improved iron status in participants but to other nutrient deficiencies or differences in access to health care and health and nutrition education.

Energy needs are increased during pregnancy and lactation. These increased energy needs may be met through partitioning of nutrients for energy utilization which is under hormonal control. The objective of the present studies was to determine if changes in plasma leptin occurred during pregnancy and lactation and if the changes were related to prolactin. Plasma leptin and prolactin were measured longitudinally in 9 women through pregnancy and lactation. In a second study, leptin and prolactin were measured 4 days and 28 days postpartum in 21 lactating women. Mean plasma leptin during the three trimesters of pregnancy was significantly higher (29.3+/-2.8 ng/ml) when compared to mean leptin during the three time periods of lactation (19.3+/-3.2 ng/ml) and control groups (9.8+/-1.4 ng/ml). Plasma leptin was elevated early in pregnancy and remained elevated throughout pregnancy. In the second study, the mean plasma leptin in the lactating women was significantly higher 4 days postpartum (17.3+/-3.7 ng/ml) and 28 days postpartum (19.2+/-3.9 ng/ml) when compared to controls (11.6+/-1.2 ng/ml). Prolactin in the control subjects (24+/-4 ng/ml) was significantly lower than in the pregnant (202+/-16 ng/ml) and lactating (108+/-26 ng/ml) groups. Similar observations were made in the second study (controls 20+/-2 ng/ml; lactation 28 days 159+/-21 ng/ml). Leptin during lactation was lower than in pregnancy but higher than control subjects. Regression analysis suggested that BMI and prolactin can be used as predictors of leptin in pregnancy and lactation. The increase in leptin and prolactin early in pregnancy suggests an association between the two hormones. Results of the present studies and research done by other investigators presents a strong role for leptin during pregnancy and lactation. Leptin is regulated by factors other than adiposity especially in reproductive women leading to our hypothesis that there are leptin and prolactin mediated effects on substrates used for energy utilization during pregnancy and lactation.

Chromium metabolism of lactating women was evaluated by measuring diet, breast milk, urine, and serum chromium in 17 subjects 60 d postpartum. Breast milk chromium concentration was similar for the 3 d of collection with a mean +/- SE concentration of 3.54 +/- 0.40 nmol/L (0.18 ng/mL). Dietary intake and urinary chromium values were also similar for each of the 3 collection days. Total chromium intake of lactating mothers (0.79 +/- 0.08 mumol/d) was greater than that of reference female subjects (0.48 +/- 0.02). There was a significant correlation (r = 0.84) between serum chromium and urinary chromium excretion. If a breast milk volume of 715 mL is assumed, chromium intake of exclusively breast-fed infants is < 2% of the estimated safe and adequate daily intake of 10 micrograms. In summary, breast milk chromium content is independent of dietary chromium intake and serum or urinary chromium values. Chromium intake also did not correlate with serum or urine chromium but there was a significant relationship between serum and urinary chromium concentrations.

The bioavailability and metabolism of different chemical species of mineral nutrients in the diet are receiving much attention from research nutritionists. In order to make scientifically based recommendations for mineral intakes, the chemical form of the mineral, with its specific absorption, utilization and retention, needs to be considered. Selenium is an example of an essential nutrient that is consumed in several different chemical forms, hence information is needed on the bioavailability and metabolism of each form before recommendations for dietary intakes can be made. A valuable tool for research on bioavailability and metabolism in humans is stable isotope tracers. When there are more than two stable isotopes available, as with selenium, stable isotope methodology allows the comparison of the utilization of different chemical forms of the nutrient simultaneously in in vivo studies. As an example of speciation questions addressed by nutritionists, a study is described that simultaneously evaluated utilization (absorption, retention and appearance in milk and blood) of two different chemical forms of selenium (selenite and selenomethionine) in lactating, non-lactating and never pregnant women using stable isotope tracers. All three groups of women had similar selenium status at the start of the study. Significantly more selenium from selenomethionine than from selenite was absorbed and appeared in the plasma in all groups. Milk contained more selenium from apparently absorbed selenomethionine than from selenite. All groups retained significantly more selenium from selenomethionine than from selenite; lactating women retained more selenium from selenite than did the other two groups, suggesting that milk losses may be partially compensated by enhanced retention of dietary selenium as selenite. Absorption and retention of selenium from selenomethionine in lactating women did not appear to be different from the other groups. The different chemical forms of selenium are metabolized differently among different physiological groups of women.

We examined utilization of selenomethionine (SeMet) and selenite in six lactating (L) and six nonlactating (NL) women, 2-3 mo postpartum, and seven never-pregnant (NP) women by use of stable-isotope tracers. All groups had similar selenium status at the start of the study. Significantly more selenium from SeMet than from selenite was absorbed and appeared in plasma in all groups. Milk contained more selenium from apparently absorbed SeMet than from selenite. More selenium from apparently absorbed selenite than from SeMet appeared in urine of NP and NL subjects whereas L subjects had approximately the same amount of selenium from apparently absorbed selenite and SeMet in their urine. All groups retained significantly more selenium from SeMet than from selenite; L women retained more selenium from selenite than did the other two groups. Absorption and retention of selenium from SeMet in L women did not appear to be significantly different from that in other women, suggesting that selenium requirements during lactation are increased mainly because of milk losses.

A separation method is described for rapidly removing zinc from interfering matrix components, such as chloride, from digested biological samples prior to measurement of zinc stable isotopes by ICP-MS. The method employs chelation of the zinc with trifluoroacetylacetone (TFA), extraction of the chelate with hexane, destruction of the chelate and dissolution of the zinc into nitric acid for determintion. Complete separation of the zinc from matrix salts is achieved, and the method does not employ chlorinated hydrocarbon solvents as used in earlier, similar schemes. Cerium from borosilicate glass tubes used in sample digestion was found to be a potential problem when measuring 70Zn, owing to the presence of 140Ce2+. This potential problem can be avoided by using quartz digestion tubes and/or correcting for any cerium by monitoring m/z 140. Accuracy was verified by an independent method, and examples of the use of stable isotopes of zinc as metabolic tracers in human metabolism are given. The detection limit for the ID method (3s of blank) was 0.7 µg Zn. An in-house urine pool was found to contain 1.18 ± 0.005 µg g–1 of Zn (n= 3) by ID and 1.17 ± 0.006 µg g–1 of Zn (n= 3) by AAS.

During lactation there is an increased maternal loss of the essential trace element zinc that is secreted into milk. During the first six months of lactation a mean of approximately 1.1 mg d–1 of zinc is secreted into human milk, which decreases to 0.6 mg d–1 during the next six months of lactation. The increased maternal need for zinc must be met through an increased dietary intake or homeostatic mechanisms which could compensate for the secretion of zinc into milk. These homeostatic mechanisms may include an increase in absorption, reduced excretion (urine and faecal endogenous losses) and the use of maternal pools of zinc, such as bone. Enhanced zinc absorption during lactation has been reported for lactating women whose intake of zinc is less than half of the current recommendation. Urinary zinc excretion by lactating women has also been observed to be significantly decreased up to 6 months pospartum compared to women who have never been pregnant. Approximately 30% of total body zinc is associated with bone. During lactation maternal bone resorption and reduction in bone mineral content has been observed. Since urinary zinc excretion is reduced during lactation, this bone resorption could supply a portion of the zinc that is incorporated into milk. Thus, during lactation, homeostatic mechanisms which include an enhanced zinc absorption, reduced urinary zinc excretion and zinc from bone resorption could partially compensate for the secretion of zinc into human milk. These homeostatic mechanisms need to be considered when dietary recommendations for zinc intake are made for lactating women.

The relationship of age with dietary intake and plasma concentrations of zinc, copper, iron, magnesium, and selenium was investigated in 36 free-living healthy men, in age ranges 25–35, 45–55, and 65–75 years (n=12/group). Three day average daily dietary intakes of energy, protein, zinc, copper, magnesium, and iron were not significantly different among groups. Plasma concentrations of zinc, copper, iron, magnesium, and selenium were also not significantly different among groups. Dietary intakes of zinc, copper, iron, and magnesium were not correlated with the plasma concentration of the respective mineral. Age was signficantly correlated with dietary magnesium intake (r=−0.37, p

ABSTRACIThis study was undertaken to investigate the effect ofpregnancy and glucose loading on zinc metabolism. In a completely random design with repeated measures, 18 non- pregnant women, 16 early-pregnant women (13-17 wk), and 16 late-pregnant women (28-34 wk) had blood collected at 0, 30, 60, 120, and 180 mm after ingesting 100 g glucose to evaluate changes in variables ofZn nutriture. Fasting plasma Zn concentrations decreased significantly as pregnancy progressed. Late-pregnant women had significantly higher erythrocyte Zn levels and greater 24-h urinary Zn and glucose excretions. Erythrocyte Zn responses to glucose load- ing were unaffected by gestational age. Plasma Zn after a glucose load in nonpregnant women exhibited a curvilinear response whereas pregnant women showed no change. This lack of response by pregnant women may be related to their lower plasma Zn concentrations. Plasma Zn in pregnant women may not be as readily available to assist in glucose utilization. Am JClin Nutr l988;48:664-70.

The mean dietary intakes of total and glycosylated vitamin B-6, determined from analysis of 3-d diet composites collected from 30 lactating women, were 8.63 +/- 4.04 and 1.33 +/- 0.85 mumol/d (mean +/- SD), respectively. A comparison of linear regression models that either included or excluded dietary glycosylated vitamin B-6 content indicates that the intake of glycosylated vitamin B-6 had little, if any, effect upon maternal plasma pyridoxal 5'-phosphate concentration and maternal urinary excretion of total vitamin B-6 and 4-pyridoxic acid. On the basis of guidelines from the literature for evaluating biochemical indices of vitamin B-6 nutriture, the women appeared to be consuming adequate amounts of the vitamin. The mean breast-milk concentrations of total and glycosylated vitamin B-6 were 733 and 18 nmol/L, respectively. Infant plasma pyridoxal 5'-phosphate concentration was 54 +/- 44 nmol/L (mean +/- SD) and all infants had lengths and weights appropriate for age.

We investigated the effect of age on indices of vitamin B-6 metabolism in 36 fasting males aged 25-35, 45-55, and 65-75 y who ingested 17.15 mumol vitamin B-6. There were no significant differences among groups in dietary vitamin B-6 intake, base-line erythrocyte pyridoxal 5'-phosphate (PLP), and total vitamin B-6 concentrations, and 24-h and base-line urinary excretion of total vitamin B-6 and 4-pyridoxic acid (4-PA). Base-line plasma PLP and total vitamin B-6 were higher (p less than 0.05) in the youngest group. Increased serum alkaline phosphatase (AP) and decreased dietary vitamin B-6 intake were correlated with decreased base-line plasma PLP and total vitamin B-6. Changes in plasma and erythrocyte PLP concentrations and excretion of 4-PA and total vitamin B-6 postload were not different among groups. Indices of vitamin B-6 absorption, phosphorylation, and excretion were not affected by age.