A moderately high intake compared to a low intake of zinc depresses magnesium balance and alters indices of bone turnover in postmenopausal women

OBJECTIVES

To determine whether moderately high or low intakes of zinc adversely affect the copper status of postmenopausal women to result in unfavorable changes in calcium and magnesium metabolism and other indicators of bone turnover.

DESIGN

After a 10-day equilibration period in which the diet provided 31.5 micromol (2 mg) Cu and 137.7 micromol (9 mg) Zn/8.4 MJ (2000 kcal), the subjects were randomly divided into two groups, with one group fed the basal diet supplemented to provide 15.7 micromol (1 mg) Cu/8.4 MJ, and the other group fed the same diet supplemented to provide 47.2 micromol (3 mg) Cu/8.4 MJ. After equilibration, both groups were fed the basal diet with no zinc supplemented (provided 45.9 micromol [3 mg] Zn/8.4 MJ) for 90 days; this was followed by another 10-day equilibration period before the basal diet was supplemented with zinc to provide 811 micromol (53 mg)/8.4 MJ for 90 days.

SETTING

The metabolic unit of the Grand Forks Human Nutrition Research Center, Grand Forks, ND, USA.

SUBJECTS

A total of 28 postmenopausal women recruited by advertisement throughout the United States of America. Among them, 25 women (64.9+6.7 y) completed the study; 21 as designed.

RESULTS

The moderately high intake compared to the low intake of zinc increased the excretion of magnesium in the feces and urine, which resulted in a decreased magnesium balance. In the women fed low dietary copper, plasma osteocalcin was higher during the low-zinc than high-zinc dietary period. The urinary excretion of N-telopeptides was increased and the serum calcitonin concentration was decreased by high dietary zinc regardless of dietary copper.

CONCLUSIONS

A moderately high intake of zinc (811 micromol/day; 53 mg/day) did not induce changes in copper metabolism that resulted in unfavorable changes in bone or mineral metabolism. However, low dietary zinc (45.9 micromol/day; 3 mg/day) apparently resulted in undesirable changes in circulating calcitonin and osteocalcin. As a moderately high intake of zinc decreased magnesium balance, further study of the possibility that a high intake of zinc is a health concern for individuals consuming less than the recommended amounts of magnesium is warranted.

Low dietary zinc alters indices of copper function and status in postmenopausal women

OBJECTIVES

To better define the relationship between dietary zinc and copper for humans so that sound recommendations for intakes of these elements can be made.

METHODS

A study was conducted to ascertain the effect of moderately excessive and deficient intakes of zinc on copper metabolism and use in humans fed low and luxuriant amounts of copper. Twenty-one postmenopausal women housed in a metabolic unit completed the study as designed. After a 10-d equilibration period in which they were fed a diet providing 31.5 micromol (2 mg) Cu and 91.8 micromol (9 mg) Zn/8.4 MJ (2000 kcal), the women were divided into two groups. One group was fed a diet containing 15.7 micromol (1 mg) Cu/8.4 MJ (2000 kcal), and the other group was fed a diet containing 47.2 micromol (3 mg) Cu/8.4 MJ (2000 kcal). After equilibration, both groups were fed the basal diet providing 45.9 micromol (3 mg) Zn/8.4 MJ (2000 kcal) for 90 d; this was followed by another 10-d equilibration period before dietary zinc was increased to 811 micromol (53 mg)/8.4 MJ (2000 kcal) for 90 d.

RESULTS

The women were in positive copper balance only when the diet provided 47.2 micromol (3 mg) Cu and 811 micromol (53 mg) Zn/d. Immunoreactive ceruloplasmin concentrations and platelet cytochrome-c oxidase activity on a platelet number basis were significantly lower and the ratio between enzymatic and immunoreactive ceruloplasmin was significantly higher during low dietary than during high dietary zinc intake. Serum cholesterol was higher in subjects fed 15.7 micromol (1 mg) Cu/d than in those fed 47.2 micromol (3 mg) Cu/d. Total and low-density lipoprotein cholesterol concentrations decreased with zinc supplementation. Whole-blood glutathione concentration and erythrocyte glutathione peroxidase activity were lower during high than during low dietary zinc intake.

CONCLUSIONS

The findings indicate that an inadequate intake of zinc (45.9 micromol/d; 3 mg/d) was more effective than a moderately high intake of zinc (811 micromol/d; 53 mg/d) in inducing changes associated with a decreased copper status in postmenopausal women. Furthermore, the findings indicate that copper status indicators might be useful in evaluating changes in zinc status in humans, and an intake of 15.7 micromol (1 mg)/d of copper may be inadequate for postmenopausal women.

Interactions among dietary fat, mineral status, and performance of endurance athletes: a case study

In a pilot study, performance measures and mineral metabolism were assessed in 3 male endurance cyclists who consumed isoenergetic, isonitrogenous diets for 28-day periods in a randomized, crossover design in which dietary carbohydrate, polyunsaturated, or saturated fat contributed about 50% of daily energy intake. Peak aerobic capacity [62 ml/(kg á min)] was unaffected by diet. Endurance capacity at 70-75% peak aerobic capacity decreased with the polyunsaturated fat diet. Copper retention tended to be positive only with saturated fat. Less iron and zinc were retained (intake - losses), and fecal losses of these minerals increased with the polyunsaturated fat. Blood biochemical measures of trace element nutritional status were unaffected by diet, except serum ferritin, which tended to decrease during consumption of the polyunsaturated fat diet. These preliminary results suggest that diets high in polyunsaturated fat, particularly linoleic acid, impair absorption and utilization of iron and zinc, and possibly magnesium, and may reduce endurance performance.

Changes in dietary zinc and copper affect zinc-status indicators of postmenopausal women, notably, extracellular superoxide dismutase and amyloid precursor proteins

BACKGROUND

Zinc is an essential trace element for human health and well-being; however, methods currently available for the assessment of zinc status in humans are unsatisfactory.

OBJECTIVE

The objective was to critically evaluate the use of various indicators of zinc status in humans in a controlled metabolic ward study.

DESIGN

Indicators of zinc status were measured in 25 healthy postmenopausal women aged 64.9 +/- 6.7 y. After a 10-d equilibration period, volunteers consumed a diet with either a low (1 mg/d; n = 12) or a high (3 mg/d; n = 13) copper content based on a total energy content of 8.4 MJ. They received the same amount of copper throughout the study. Both groups were fed the basal diet (3 mg Zn/d) with no zinc supplement for one 90-d period, and the diet supplemented with 50 mg Zn/d for another 90-d period.

RESULTS

Zinc supplementation significantly increased (P < 0.0001) extracellular but not erythrocyte superoxide dismutase activity. This increase was more apparent when subjects were fed the low-copper diet. Zinc supplementation in combination with the low-copper diet significantly decreased (P < 0.01) amyloid precursor protein expression in platelets. Other indicators of zinc status that were significantly elevated after zinc supplementation were as follows: plasma zinc and free thyroxine concentrations and mononuclear 5'-nucleotidase activity.

CONCLUSION

The measurement of serum extracellular superoxide dismutase activity may be useful as a marker for the functional assessment of zinc status in humans.

The interaction between dietary fructose and magnesium adversely affects macromineral homeostasis in men

OBJECTIVE

Studies with rats have found that an interaction between fructose and magnesium affects macromineral metabolism; high dietary fructose significantly increased kidney calcification in both male and female rats, particularly when dietary magnesium was low. This study tests the hypothesis that an interaction between dietary fructose and magnesium adversely affects macromineral homeostasis in men.

METHODS

Eleven men aged 22 to 40 years were fed a mixed, Western diet for four 42-day dietary periods in which dietary magnesium was either approximately 170 or 370 mg/day and dietary fructose was either 4% or 20% of energy. A decaffeinated beverage containing high fructose corn syrup replaced cornstarch, bread and rice in the low fructose diet to give the high fructose diet.

RESULTS

High dietary fructose significantly (p<0.01) increased magnesium balance during both low and high dietary magnesium intakes. Ultrafilterable and ionized serum magnesium also apparently were related to magnesium and fructose intakes; they were higher when fructose was fed and when Mg intakes were high. High fructose depressed calcium balance: the effect tended to be more marked when dietary Mg was low. High dietary fructose also significantly (p<0.005) decreased phosphorous balance. Urinary phosphorous losses were significantly (p<0.001) higher when high dietary fructose was fed. High dietary fructose also increased the concentration of serum alkaline phosphatase (p<0.005).

CONCLUSION

These findings indicate that dietary fructose adversely affects macromineral homeostasis in humans and suggest further studies to see if a high fructose diet coupled with low dietary magnesium and marginal calcium leads to bone loss.

Copper intake and assessment of copper status

The diagnosis of marginal copper deficiency has not been perfected despite an increased understanding of the physiologic roles of copper. The use of nonstandardized procedures and the effects of factors other than copper nutriture have impeded identification of an ideal indicator of copper nutritional status in humans. A review of studies of experimental copper deprivation conducted in adult humans over the past 12 y indicated that between 1.0 and 1.25 mg Cu/d is needed by adults for copper maintenance for periods of up to 6 mo and that < or = 2.6 mg Cu/d for periods of up to 42 d is not sufficient for recovery from copper deprivation. Copper-containing enzymes in blood cells, such as erythrocyte superoxide dismutase and platelet cytochrome-c oxidase, may be better indicators of metabolically active copper and copper stores than plasma concentrations of copper or ceruloplasmin because the enzyme activities are sensitive to changes in copper stores and are not as sensitive to factors not related to copper nutriture.

Chromium supplementation and resistance training: effects on body composition, strength, and trace element status of men

The effects of 8 wk of daily chromium supplementation (3.3-3.5 mumol as chromium chloride or chromium picolinate) or placebo (0.1 mumol Cr) and weight training were examined in 36 men in a double-blind design. Strength, mesomorphy, fat-free mass, and muscle mass increased with resistance training independently of chromium supplementation (P < 0.0001). Protein, magnesium, zinc, copper, and iron intakes equalled or exceeded the recommended dietary allowance (RDA) or estimated safe and adequate daily dietary intake (ESADDI) during training and did not change significantly from pretraining intakes (P > 0.05). Chromium supplementation increased the serum chromium concentration and urinary chromium excretion without a difference as a result of the chemical form of chromium (P < 0.05). Resistance training was associated with a significant decrease (P < 0.05) in serum ferritin, total-iron-binding capacity, transferrin saturation, the ratio of enzymatic to immunoreactive ceruloplasmin, and plasma copper, independently of chromium supplementation. However, transferrin saturation was decreased more with chromium picolinate supplementation (24%) than with chromium chloride or placebo (10-13%). Compared with pretraining values, urinary magnesium excretion increased (P < 0.05) and urinary zinc output tended to decrease during the first 4 wk of resistance training and then returned to baseline values for the final 4 wk, which suggests an adaptation in mineral excretion in response to weight training. These findings suggest that routine chromium supplementation has no beneficial effects on body- composition change or strength gain in men. Whether chromium supplementation of individuals with diminished chromium nutriture facilitates propitious changes in body structure and function remains to be determined.

Effects of a diet low in copper on copper-status indicators in postmenopausal women

To study the effects of low copper intake in older individuals, 12 postmenopausal women, aged 63.1 +/- 8.8 y, were fed a diet containing 9 micromol (0.57 mg) Cu/d for 105 d, followed by a copper-repletion period of 35 d during which the diet was supplemented with 31.5 micromol (2.0 mg) Cu/d. Plasma copper and ceruloplasmin did not change significantly during copper depletion but ceruloplasmin decreased during copper repletion. Erythrocyte superoxide dismutase activity dropped significantly during low copper intake from 3450 to 2600 U/g hemoglobin, but did not increase during copper repletion. Platelet cytochrome c oxidase activity changed significantly (P<0.0001) from 1740 to 810 U/g protein during copper depletion, then increased to 1000 U/g protein during copper repletion. Erythrocyte glutathione peroxidase activity responded similarly. Clotting factor VIII activity increased significantly during copper depletion, then dropped during copper repletion. Low copper intakes did not induce the changes in serum cholesterol and hematology generally found in copper-deficient animal models. These results indicate that a paradigm shift may be needed in evaluating copper status in adult humans. Sensitive indicators of copper include functional activities of platelet cytochrome c oxidase, platelet copper, glutathione peroxidase, and clotting factor VIII. Plasma copper, ceruloplasmin, and cholesterol are relatively insensitive indicators. Also, the recovery from mild copper depletion may require more aggressive intervention tha 2 mg Cu/d for 35 d.

Assessment of copper nutritional status

Despite increased interest in the role of copper deficiency in clinical problems and an increased understanding of the physiological roles of copper, the diagnosis of a marginal deficiency has not been perfected. The use of non-standardized procedures and the effects of factors other than copper nutriture have impeded identification of the "ideal" indicator of copper nutritional status in adult humans. The specific activity of copper enzymes, or of copper-containing enzymes in blood cells, such as erythrocyte superoxide dismutase and platelet or leukocyte cytochrome c oxidase, may be a better indicator of metabolically active copper stores than the serum concentration of copper or ceruloplasmin, because the enzyme activities are sensitive to changes in copper stores and are not as sensitive to factors not related to copper nutriture. A single index, such as serum copper concentration, is inadequate for assessing the total body copper nutriture of an individual and must be supported by corroborating evidence.

Assessment of copper nutritional status

Despite increased interest in the role of copper deficiency in clinical problems and an increased understanding of the physiological roles of copper, the diagnosis of a marginal deficiency has not been perfected. The use of non-standardized procedures and the effects of factors other than copper nutriture have impeded identification of the "ideal" indicator of copper nutritional status in adult humans. The specific activity of copper enzymes, or of copper-containing enzymes in blood cells, such as erythrocyte superoxide dismutase and platelet or leukocyte cytochrome c oxidase, may be a better indicator of metabolically active copper stores than the serum concentration of copper or ceruloplasmin, because the enzyme activities are sensitive to changes in copper stores and are not as sensitive to factors not related to copper nutriture. A single index, such as serum copper concentration, is inadequate for assessing the total body copper nutriture of an individual and must be supported by corroborating evidence.

Biochemical assessment of vitamins and trace metals

The choice of nutritional assessment tests must be made with care, as the available tests may reflect recent dietary intakes or body tissue stores to different degrees. The interpretation of nutritional assessment tests is complicated by the dynamic nature and broad range of nutrient intake and metabolism and by a relative lack of age- and sex-specific reference ranges. The latter problem can be minimized by the use of function-based methods, such as the measurement of vitamin-dependent red cell enzyme activities to assess B vitamin status; however, few suitable function-based methods are now available, and more research in this area is needed. Because calibration standards and quality control materials may not be readily available, laboratory analysts planning nutritional assessment testing must be especially careful in establishing the credibility of assays and the quality control program. Recent advances in analytic methodology include the specificity offered by HPLC techniques and methodologies that provide simultaneous determination of more than one nutrient (or form of nutrient) in a single procedure. Examples of the latter include HPLC methods that provide B vitamin or fat-soluble vitamin profiles, and emission spectrometry techniques that provide trace metal profiles. Further work in providing useful nutritional assessment profiles and convenient automated methods is needed.

Assessment of copper status: effect of age and gender on reference ranges in healthy adults

We measured major indices related to copper nutritional status in 55 men and 86 women between ages 20 and 83 years who were in apparent good health. Plasma copper concentrations and both immunoreactive and enzymatically measured ceruloplasmin were significantly higher in women than in men and were higher in women taking oral contraceptives. Plasma copper, immunoreactive ceruloplasmin, and cytochrome-c oxidase in platelets and mononucleated leukocytes tended to increase with age. The ratio of enzymatic to immunoreactive ceruloplasmin, erythrocyte superoxide dismutase, and 67Cu uptake by erythrocytes were not significantly affected by either age or gender. Thus, factors other than copper nutriture--such as age, gender, and hormone use--need to be considered when using many of these indicators to evaluate copper nutritional status.

Assessment of copper status: effect of age and gender on reference ranges in healthy adults

We measured major indices related to copper nutritional status in 55 men and 86 women between ages 20 and 83 years who were in apparent good health. Plasma copper concentrations and both immunoreactive and enzymatically measured ceruloplasmin were significantly higher in women than in men and were higher in women taking oral contraceptives. Plasma copper, immunoreactive ceruloplasmin, and cytochrome-c oxidase in platelets and mononucleated leukocytes tended to increase with age. The ratio of enzymatic to immunoreactive ceruloplasmin, erythrocyte superoxide dismutase, and 67Cu uptake by erythrocytes were not significantly affected by either age or gender. Thus, factors other than copper nutriture--such as age, gender, and hormone use--need to be considered when using many of these indicators to evaluate copper nutritional status.

Homeostatic control of zinc metabolism in men: zinc excretion and balance in men fed diets low in zinc

Zinc metabolism was studied in 11 men. The study began with 28-d equilibration when dietary zinc was 159 mumol/d (X), followed by 35-d periods when the diet contained 21.9 (I), 37.5 (II), 51.6 (III), or 67.8 (IV) mumol Zn/d in random order, and ended with 35 d with X. The diet was conventional foods and egg white protein. Zinc balance, including surface and semen losses, was zero only during I. Semen zinc was unaffected by diet. Plasma zinc dropped to 0.44 and 0.49 mumol/L in two subjects during I and was significantly decreased during I compared with X (P < 0.0002). Urinary zinc declined with decreasing zinc intake. A combination of urinary and plasma zinc criteria from Baer and King (Am J Clin Nutr 1984; 39:556-70) could be used to distinguish stages of zinc deficiency. By these criteria, no subjects were deficient during IV, one was marginally deficient during III, three were marginally deficient during II, and seven were deficient during I.

Effects of age and sex on copper absorption, biological half-life, and status in humans

Healthy, free-living men and women aged 20-83 y (n = 127) were studied to determine the effects of age and sex on copper absorption, biological half-life (BH), and status. Copper absorption was greater in women (71%) than in men (64%) aged 20-59 y (P = 0.02), but did not differ in men and women aged 60-83 y. BH of 67Cu ranged from 13 to 33 d and differed between men and women aged 20-59 y (P = 0.006), but not between men and women aged 60-83 y. Plasma copper, enzymatic ceruloplasmin (Cp), and immunoreactive (RID) Cp were significantly higher in women than in men (P < 0.005), but superoxide dismutase (SOD) and in vitro 67Cu uptake by red blood cells did not differ. Plasma copper, RID Cp, and cytochrome oxidase in platelets and mononuclear cells were significantly affected by age (P < 0.005). Oral contraceptives elevated plasma copper, enzymatic Cp, and SOD activity but not copper absorption and BH in women aged 20-39 y. Copper intake from self-selected diets was 0.9-1.2 mg/d for women and 1.2-1.3 mg/d for men, but net copper absorption (micrograms Cu.kg body wt-1.d-1) did not differ. Thus, dietary copper intake requirements may differ between men and women.

Short- and Long-Term Variability of Selected Indices Related to Nutritional Status. II. Vitamins, Lipids, and Protein Indices

Five free-living women (ages 23-38 years) who consumed a self-selected diet and five women (ages 23-44 years) residing in a metabolic unit who were fed constant diet were assessed for variation in vitamin and general chemistry indices. Blood was drawn from these women once a month for five months, once a week for five weeks, and once a day for five days to assess analytical and biological variability of the indices. Analytical variability was determined by concurrently analyzing control samples prepared from plasma and serum pools. All samples were analyzed in duplicate. Of the measured indices, vitamins and lipids seemed to be the most variable. Diet had a significant effect only on ascorbic acid. We were unable to show any seasonal change for these analytes. Estimations of analytical variability, along with estimates of biological variability, and knowledge of dietary practices are essential when interpreting differences in analytes.

Short- and long-term variability of selected indices related to nutritional status. II. Vitamins, lipids, and protein indices

Five free-living women (ages 23-38 years) who consumed a self-selected diet and five women (ages 23-44 years) residing in a metabolic unit who were fed constant diet were assessed for variation in vitamin and general chemistry indices. Blood was drawn from these women once a month for five months, once a week for five weeks, and once a day for five days to assess analytical and biological variability of the indices. Analytical variability was determined by concurrently analyzing control samples prepared from plasma and serum pools. All samples were analyzed in duplicate. Of the measured indices, vitamins and lipids seemed to be the most variable. Diet had a significant effect only on ascorbic acid. We were unable to show any seasonal change for these analytes. Estimations of analytical variability, along with estimates of biological variability, and knowledge of dietary practices are essential when interpreting differences in analytes.

Nutrition status and brain function in aging

Biochemical indices of nutrition status assessed in 28 healthy persons aged greater than 60 y were related to cognitive performance and electroencephalographic (EEG) indices of neuropsychological function. Performance data were most frequently related to indices of nutrition status when tasks were demanding. Numerous correlations were also found between EEG indices and indices of thiamin, riboflavin, and iron nutriture. Certain observations, such as a decrement in alpha-wave activity in the EEG of subjects with low thiamin status, suggest that subtle neuropsychological impairment can occur in association with mild deficits in nutrition status. Other findings indicate that EEG frequency responses of older subjects with high iron status are similar to those of younger persons; however, these data are more difficult to interpret. The results suggest that further research on nutrition and neuropsychological function will lead to a better understanding of the role of nutrition in maintaining the functional integrity of the aging brain.

Manganese content of the cellular components of blood

We measured the manganese content of whole blood, plasma, platelets, mononucleated cells, polymorphonucleated cells, and erythrocytes. Platelets and blood cells were separated from whole blood by use of discontinuous gradients of colloidal polyvinylpyrrolidone-coated silica (Percoll), and their manganese content was measured by Zeeman graphite furnace atomic absorption spectrophotometry, after digestion with nitric acid and hydrogen peroxide. Erythrocytes account for about 66% of the manganese in whole blood, whereas the "buffy coat"--platelets and leukocytes--accounts for about 30%. The "buffy coat" components turn over more rapidly than do erythrocytes, so their manganese content may better indicate the body's manganese status.

Response of various indices of iron status to acute iron depletion produced in menstruating women by low iron intake and phlebotomy

We investigated response sensitivities of indices of iron status to controlled iron depletion and repletion in 11 premenopausal women. The women were depleted of storage iron (as reflected by serum ferritin) through a combination of a low-iron diet and phlebotomy. They then consumed a diet containing 13.7 mg of iron per 2000 kcal, supplemented with either ascorbic acid or placebo (for 5 1/2 weeks) and a daily 50-mg iron supplement (for the subsequent 17 days). The relative sensitivities of different indices for detecting iron depletion were as follows: ferritin greater than % transferrin saturation greater than plasma iron greater than hemoglobin greater than hematocrit greater than zinc protoporphyrin (ZnPP) and erythrocyte protoporphyrin (EP). Ascorbic acid treatment during repletion, before iron supplementation, significantly (P less than 0.05) affected changes in hemoglobin, ZnPP, ZnPP/heme, and EP/heme. Changes in heme synthesis evidently do not occur until iron stores are depleted and, conversely, during iron repletion hematopoiesis must be satisfied before iron stores, as reflected by ferritin, increase. Thus, the use of only one index of iron status is of limited value for detecting iron depletion.

Manganese content of the cellular components of blood

We measured the manganese content of whole blood, plasma, platelets, mononucleated cells, polymorphonucleated cells, and erythrocytes. Platelets and blood cells were separated from whole blood by use of discontinuous gradients of colloidal polyvinylpyrrolidone-coated silica (Percoll), and their manganese content was measured by Zeeman graphite furnace atomic absorption spectrophotometry, after digestion with nitric acid and hydrogen peroxide. Erythrocytes account for about 66% of the manganese in whole blood, whereas the "buffy coat"--platelets and leukocytes--accounts for about 30%. The "buffy coat" components turn over more rapidly than do erythrocytes, so their manganese content may better indicate the body's manganese status.

Response of various indices of iron status to acute iron depletion produced in menstruating women by low iron intake and phlebotomy

We investigated response sensitivities of indices of iron status to controlled iron depletion and repletion in 11 premenopausal women. The women were depleted of storage iron (as reflected by serum ferritin) through a combination of a low-iron diet and phlebotomy. They then consumed a diet containing 13.7 mg of iron per 2000 kcal, supplemented with either ascorbic acid or placebo (for 5 1/2 weeks) and a daily 50-mg iron supplement (for the subsequent 17 days). The relative sensitivities of different indices for detecting iron depletion were as follows: ferritin greater than % transferrin saturation greater than plasma iron greater than hemoglobin greater than hematocrit greater than zinc protoporphyrin (ZnPP) and erythrocyte protoporphyrin (EP). Ascorbic acid treatment during repletion, before iron supplementation, significantly (P less than 0.05) affected changes in hemoglobin, ZnPP, ZnPP/heme, and EP/heme. Changes in heme synthesis evidently do not occur until iron stores are depleted and, conversely, during iron repletion hematopoiesis must be satisfied before iron stores, as reflected by ferritin, increase. Thus, the use of only one index of iron status is of limited value for detecting iron depletion.

Short-term and long-term variability of indices related to nutritional status. I: Ca, Cu, Fe, Mg, and Zn

Five free-living women (ages 28-38 y) and five women (ages 23-44 y) residing in a metabolic unit and eating a constant diet were assessed for variation in indices related to mineral nutrition. Blood was sampled once a month for five months, once a week for five weeks, and once a day for five days to assess analytical and biological variability. Analytical variability was determined by using concurrently run duplicate control samples prepared from plasma or serum pools. Of the measured indices, serum ferritin varied most, with intra-individual variance of 4.72% to 18.0%. Much of this variance may have been because of changes in iron status or in the analytical technique used. Intra-individual month-to-month variance for other indices ranged from 17% for superoxide dismutase (EC 1.15.1.1) to 1.5% for calcium. Correction for long-term analytical variation indicated that most of the variance was associated with the biological component. The higher biological variabilities of some indices, including ferritin or superoxide dismutase, need to be considered when nutritional status is being evaluated or when serial observations are made over a protracted period in clinical studies or trials.

Short-term and long-term variability of indices related to nutritional status. I: Ca, Cu, Fe, Mg, and Zn

Five free-living women (ages 28-38 y) and five women (ages 23-44 y) residing in a metabolic unit and eating a constant diet were assessed for variation in indices related to mineral nutrition. Blood was sampled once a month for five months, once a week for five weeks, and once a day for five days to assess analytical and biological variability. Analytical variability was determined by using concurrently run duplicate control samples prepared from plasma or serum pools. Of the measured indices, serum ferritin varied most, with intra-individual variance of 4.72% to 18.0%. Much of this variance may have been because of changes in iron status or in the analytical technique used. Intra-individual month-to-month variance for other indices ranged from 17% for superoxide dismutase (EC 1.15.1.1) to 1.5% for calcium. Correction for long-term analytical variation indicated that most of the variance was associated with the biological component. The higher biological variabilities of some indices, including ferritin or superoxide dismutase, need to be considered when nutritional status is being evaluated or when serial observations are made over a protracted period in clinical studies or trials.

Effects of dietary copper on human autonomic cardiovascular function

Heart rate and blood pressure responses during supine rest, orthostasis, and sustained handgrip exercise at 30% maximal voluntary contraction were determined in eight healthy women aged 18-36 years who consumed diets varying in copper and ascorbic acid content. Copper retention and plasma copper concentration were not affected by diet. Enzymatic, but not immunoreactive, ceruloplasmin was lower (p less than 0.05) after the low copper and high ascorbic acid diet periods. Diet had no effect on resting supine heart rates, orthostatic responses in heart rate and blood pressure, or standing resting blood pressure. Systolic and diastolic blood pressures were increased significantly (p less than 0.05) during the handgrip test at the end of the low copper and ascorbic acid supplementation periods. Also, the ratio of enzymatic to immunoreactive ceruloplasmin decreased significantly during these dietary treatments. The mean arterial blood pressure at the end of the handgrip test was negatively (p less than 0.0004) correlated with the ceruloplasmin ratios. These findings indicate a functional alteration in human blood pressure regulation during mild copper depletion.

Ethanol metabolism in postmenopausal women fed a diet marginal in zinc

Five postmenopausal women aged 50-63 y were fed a diet of mixed Western foods that supplied an average of 2.6 mg zinc/d for 6 mo. Plasma zinc did not change significantly during Zn depletion but increased slightly when Zn was fed. Zn content of blood cellular components and activities of Zn-containing enzymes were not affected by Zn intake. Ethanol tolerance tests performed at the end of control, middle of depletion, end of depletion, and end of repletion showed a change in ethanol metabolism at the end of the low-Zn intake period that was corrected within 1 mo with Zn supplementation. These data suggest that there are homeostatic mechanisms that maintain circulating levels of Zn. Zn and activity of Zn enzymes in tissues may be decreased before changes in circulating Zn levels are seen. Functional indices of Zn biochemistry, such as ethanol metabolism, may be more sensitive indicators of Zn stores and nutriture than circulating Zn.

Retinol, alpha-tocopherol, lycopene, and alpha- and beta-carotene simultaneously determined in plasma by isocratic liquid chromatography

Retinol, alpha-tocopherol, lycopene, and alpha- and beta-carotene can be simultaneously determined in human plasma by reversed-phase liquid chromatography. Plasma--0.5 mL plus added internal standard, retinyl acetate--is deproteinized with 0.5 mL of ethanol, then extracted with 1.0 mL of petroleum ether. The organic layer is removed and evaporated, the residue is redissolved in 0.25 mL of ethanol, and 8-microL samples are injected into a 60 X 4.6 mm column of Hypersil ODS 3-microns particles at 35 degrees C. An isocratic methanol mobile phase, flow rate 0.9 mL/min, is used for the 9-min run. Retinol and retinyl acetate are monitored at 305 nm, the tocopherols at 292 nm, and the carotenoids at 460 nm. Between-run CVs were 3.1, 6.9, 6.1, and 6.5% for retinol, alpha-tocopherol, lycopene, and beta-carotene, respectively. Small sample requirement, simplicity of extraction, short run time, and good reproducibility make this procedure ideal for clinical or research use.

Retinol, alpha-tocopherol, lycopene, and alpha- and beta-carotene simultaneously determined in plasma by isocratic liquid chromatography

Retinol, alpha-tocopherol, lycopene, and alpha- and beta-carotene can be simultaneously determined in human plasma by reversed-phase liquid chromatography. Plasma--0.5 mL plus added internal standard, retinyl acetate--is deproteinized with 0.5 mL of ethanol, then extracted with 1.0 mL of petroleum ether. The organic layer is removed and evaporated, the residue is redissolved in 0.25 mL of ethanol, and 8-microL samples are injected into a 60 X 4.6 mm column of Hypersil ODS 3-microns particles at 35 degrees C. An isocratic methanol mobile phase, flow rate 0.9 mL/min, is used for the 9-min run. Retinol and retinyl acetate are monitored at 305 nm, the tocopherols at 292 nm, and the carotenoids at 460 nm. Between-run CVs were 3.1, 6.9, 6.1, and 6.5% for retinol, alpha-tocopherol, lycopene, and beta-carotene, respectively. Small sample requirement, simplicity of extraction, short run time, and good reproducibility make this procedure ideal for clinical or research use.

Oxalate degradation by gastrointestinal bacteria from humans

Anaerobic bacteria that metabolize oxalic acid have only recently been isolated from the rumen and from other gastrointestinal habitats. They constitute a new genus and species, Oxalobacter formigenes. This report presents the first comparison of cultural counts of these organisms from human feces and indicates that numbers as high as 10(7)/g may be present in feces from normal humans. Rates of oxalate degradation by mixed bacterial populations in feces from seven normal humans ranged from 0.1 to 4.8 mumol/(g X h). With fecal samples from eight patients that had undergone jejunoileal bypass surgery, rates were much lower [0-0.006 mumol/(g X h)]. We propose that oxalic acid degradation by Oxalobacter formigenes may influence absorption of oxalate from the intestine and that lower rates or lack of oxalate degradation in the colons of jejunoileal bypass patients may contribute to the increased absorption of dietary oxalate and the hyperoxaluria commonly associated with such patients.

Comparison of dietary histories and seven-day food records in a nutritional assessment of older adults

Dietary histories and seven-day food records were obtained for 54 apparently healthy older adults. The two dietary methods correlated for most nutrients, but mean differences were significant for several nutrients. Intakes below recommended levels occurred most frequently for energy, calcium, and zinc. Biochemical evidence of thiamin and riboflavin deficiency was unexpectedly frequent. Using food records, dietary iron correlated with serum ferritin. Using dietary histories, dietary protein correlated with serum albumin, and dietary zinc correlated with plasma zinc. Using either dietary method, plasma ascorbate was associated positively with both dietary ascorbate and ascorbate supplements, and negatively with cigarette smoking. Use of thiamin- or folate-containing supplements was associated with improved biochemical status for the respective vitamin. Though neither dietary histories nor food records give precise intake data for individuals, either method may be useful for epidemiologic studies with appropriate sample sizes.

Zinc content of blood cellular components and lymph node and spleen lymphocytes in severely zinc-deficient rats

Several investigators have suggested that the measurement of leukocyte zinc may be useful for the assessment of zinc nutriture. However, in an earlier study, we found that the methods used did not adequately separate platelets from the different leukocyte populations. We subsequently developed a method which does adequately separate platelets, mononucleated cells (MNC), polymorphonucleated cells (PMN), and erythrocytes (RBC) from a single blood sample. This method was applied to a study of severe zinc deficiency in adult male rats. Significant reductions in plasma and femur zinc indicated severe zinc deficiency in the zinc-deficient animals compared with pair-fed or ad libitum-fed control rats in two separate experiments. However, we noted no differences in the zinc content of the MNC, PMN, RBC or lymph node lymphocytes, on a per cell basis, between the zinc-deficient and ad libitum- or pair-fed control groups of rats. A minor, but not significant (P greater than 0.05) reduction of platelet zinc was noted in zinc-deficient rats in two separate studies. These data indicate that the zinc contents of blood cellular components are not sensitive indicators of zinc deficiency in rats.

Zinc content of cellular components of blood: methods for cell separation and analysis evaluated

Platelets, mononucleated cells, polymorphonucleated cells, and erythrocytes were separated from whole blood by use of discontinuous gradients of colloidal polyvinylpyrrolidone-coated silica ("Percoll"). We measured the zinc content of these cells by flame atomic absorption spectrophotometry, using a modified technique for micro-samples that obviated matrix interferences. Thus, results obtained by conventional flame atomic absorption and by the micro-method were identical. Inter-comparisons of separation methods indicated that separation of platelets and mononucleated cells by a two-gradient system of "Ficoll-Hypaque" (a synthetic polymer of sucrose) or Percoll was relatively poor, whereas there was a good separation when a tertiary gradient system of Percoll was used. The apparent zinc content of mononucleated cells depended on the degree of separation from the platelets, with contamination by platelets resulting in artificially high values for mononucleated cells.

Zinc content of cellular components of blood: methods for cell separation and analysis evaluated

Platelets, mononucleated cells, polymorphonucleated cells, and erythrocytes were separated from whole blood by use of discontinuous gradients of colloidal polyvinylpyrrolidone-coated silica ("Percoll"). We measured the zinc content of these cells by flame atomic absorption spectrophotometry, using a modified technique for micro-samples that obviated matrix interferences. Thus, results obtained by conventional flame atomic absorption and by the micro-method were identical. Inter-comparisons of separation methods indicated that separation of platelets and mononucleated cells by a two-gradient system of "Ficoll-Hypaque" (a synthetic polymer of sucrose) or Percoll was relatively poor, whereas there was a good separation when a tertiary gradient system of Percoll was used. The apparent zinc content of mononucleated cells depended on the degree of separation from the platelets, with contamination by platelets resulting in artificially high values for mononucleated cells.

Increased cholesterol in plasma in a young man during experimental copper depletion

Signs of copper depletion were produced in a healthy man by an amount of dietary copper (0.83 mg/day) similar to that in some contemporary diets. Urinary and fecal loss of copper exceeded intake. Plasma copper, ceruloplasmin, and superoxide dismutase activity in erythrocytes decreased. Cholesterol in plasma increased, and hematologic indices were unchanged. Lipid metabolism may be a more sensitive index of copper nutriture than are changes in hematology. The findings support the hypothesis that inadequate copper nutriture or altered copper metabolism contributes to the occurrence of ischemic heart disease.

Maternal zinc, iron, folic acid, and protein nutriture and outcome of human pregnancy

Four hundred fifty women were observed during pregnancy and postpartum. Forty-three variables including 12 laboratory indices of maternal nutrient status were assessed. Of the variance in fetal weight and head circumference 9.9 and 8.1%, respectively, were predictable by polynomial stepwise regression of laboratory indices of maternal nutriture. Maternal plasma zinc levels were inversely correlated with fetal weight. The occurrence of pregnancy complications in the highest and lowest quartiles of maternal plasma zinc, albumin, iron, and folic acid were compared. Using data only from the initial blood samples for which the trimester was identified precisely (n = 394), a significant association was found between the total occurrence of fetomaternal complications and zinc and albumin levels in the lowest quartile (zinc, p less than 0.02; albumin, p less than 0.02). Low zinc or low albumin were also associated with the specific complications of fetal distress (zinc, p less than 0.002; albumin p less than 0.002). High plasma folate was also associated with the total occurrence of complications (p less than 0.008) and with fetal distress (p less than 0.002). When all data (n = 713) including repeat blood samples and data from 56 mothers in whom the trimester could not be verified precisely were evaluated, associations between other complications and lowest quartile zinc and albumin and highest quartile folate were identified. Discriminant analysis of data from the initial blood samples revealed that plasma zinc was a discriminator for fetomaternal complications only in women in the lowest quartile for plasma zinc.

Changes in plasma zinc content after exercise in men fed a low-zinc diet

For 30 days five healthy men aged 23-57 yr consumed a diet adequate in zinc (8.6 mg/day); they ate a low-zinc diet (3.6 mg/day) for the next 120 days and then received a zinc-supplemented (33.6 mg/day) diet for 30 days. Copper intake was constant at 1.8 mg/day. Aerobic capacity was determined periodically during each diet period. Relative zinc balance (% of control) declined during depletion (r = -0.28, P less than 0.009). Pre- and postexercise zinc concentrations decreased when dietary zinc was restricted (r = -0.61, P less than 0.0001 and r = -0.78, P less than 0.0001) and increased with supplementation (r = 0.61, P less than 0.008 and r = 0.76, P less than 0.0003, respectively). Both plasma zinc and hematocrit increased (P less than 0.01) after maximal exercise. To minimize the effect of hemoconcentration during exercise, the van Beaumont quotient (J. Appl. Physiol. 34: 102-106, 1973) was calculated using pre- and postexercise hematocrit and plasma zinc. The initial quotient of 1.8 +/- 1.8% (mean +/- SE) declined (P less than 0.05) to -7.4 +/- 2.3% during depletion. With zinc repletion, the quotient increased to 6.9 +/- 3.6%, which was greater (P less than 0.05) than the quotient in depletion but similar to the initial quotient. The quotient was a strong predictor (r = 0.71, P less than 0.0005) of the change in relative zinc balance during zinc depletion. In contrast, no changes were found in plasma copper content. These data suggest that zinc mobilization from tissues is impaired during zinc depletion, and they validate the use of the van Beaumont quotient as an index of change in body zinc stores.

Effect of oral folic acid supplements on zinc, copper, and iron absorption and excretion

Effects of folic acid supplements on zinc excretion patterns were seen during studies of mild zinc deficiency in men. During these studies eight men were fed diets containing 150 micrograms of folacin (by analysis) per day. Four of the men were supplemented with 400 micrograms of pteroylglutamic acid (folic acid) every other day. All of the men were fed diets containing about 3.5 mg/Zn per day which were supplemented with 4.0 mg/Zn day for 4 wk and unsupplemented for 16 wk, then supplemented with 30.0 mg/Zn day for 4 wk. Their body weights were kept constant by adjustments of energy intakes and expenditures. Duplicate diets, stools, and urines were analyzed for zinc, copper, and iron. Fecal zinc was significantly (p less than 0.001) higher in the group that received folic acid supplements during the initial control and low zinc intake periods. No significant differences were seen during the period of high zinc intake. During all dietary periods urinary zinc excretion was reduced by about 50% by folic acid supplementation. No apparent changes occurred in iron or copper excretion. These data indicate that supplemental folate influences zinc homeostasis, perhaps through formation of an insoluble chelate and impairment of absorption.

Effect of consuming fiber from corn bran, soy hulls, or apple powder on glucose tolerance and plasma lipids in type II diabetes

The effects of consuming corn bran, soy hulls, or apple powder on glucose and lipid metabolism were investigated in two studies of persons with type II diabetes. Fiber sources, completely or partially added to bread, were incorporated into subjects' self-selected diets. Low fiber white bread served as a control. In study A, 10 subjects consumed 26 g fiber source daily; in study B, eight subjects consumed 52 g fiber source. Biochemical tests, including a 2-h postprandial glucose test using a low fiber formula meal, were scheduled after 2 and 4 wk of each dietary treatment. Soy hull consumption slightly improved some measures of glucose tolerance, with results varying between the studies. Consumption of 52 g corn bran decreased very low-density lipoprotein cholesterol, triglycerides, and glycosylated Hb, but subject tolerance was poor with the particle size used. Consumption of 52 g apple powder increased low-density lipoprotein and total cholesterol levels.

Influence of type and amount of dietary lipid on plasma lipid concentrations in endurance athletes

Changes in plasma total cholesterol, triglyceride, and lipoprotein concentrations were assessed in three male endurance cyclists who consumed isoenergetic diets for 28-day periods in which carbohydrate, polyunsaturated fat, or saturated fat contributed about 50% of the daily energy intake. Dietary cholesterol was similar among the diets. Maximal aerobic capacity was maintained at 62 ml O2/(kg X min). Body weights were held within 3% of admission levels. The polyunsaturated fat diet significantly (p less than 0.05) reduced mean fasting plasma total cholesterol in comparison to the saturated fat and carbohydrate diets (160 versus 254 and 243 mg/dl, respectively). Similarly, the polyunsaturated fat diet depressed (p less than 0.05) mean plasma triglycerides relative to the saturated fat and carbohydrate diets (37 versus 62 and 79 mg/dl, respectively). No significant dietary effects were seen on high-density lipoprotein cholesterol. The observed changes in plasma total cholesterol were not significantly different than the values predicted by the Keys' equation, delta CHL = 1.35(2 delta S-delta P) + 1.5 delta Z. We conclude that under controlled conditions in which physical activity is constant l) dietary lipid differences influence fasting serum lipid and lipoprotein concentrations among men with high energy expenditures, and 2) the Keys' equation gives useful predictions of changes in plasma total cholesterol among vigorous men consuming different types and amounts of dietary lipid.

Iron status and brain function: serum ferritin levels associated with asymmetries of cortical electrophysiology and cognitive performance

Levels of serum ferritin and iron were examined in relation to cognitive performance and quantitative EEG measures in 69 normal university students. Higher levels of serum ferritin were associated with greater activation of the left hemisphere relative to the right, indicated by less power in the EEG spectra from left hemisphere electrodes. Iron status was significantly related to cognitive performance on two of the cognitive tasks, and these relationships were consistent with the EEG asymmetries: higher ferritin predicted greater verbal fluency but poorer nonverbal auditory task performance. These results suggest that body iron stores are relevant to specific neurophysiological processes supporting attention.

Severe zinc deficiency: effects on the distribution of nine elements (potassium, phosphorus, sodium, magnesium, calcium, iron, zinc, copper and manganese) in regions of the rat brain

The effect of severe zinc deficiency on the distribution of nine elements (potassium, phosphorus, sodium, magnesium, calcium, iron, zinc, copper and manganese) in brain regions (olfactory lobes, right and left hippocampi, cerebellum and the rest of the brain) has been studied. After male rats (30 days old) were fed a zinc-deficient diet for 28 days, the zinc concentration of most brain parts was similar to zinc-adequate control values. Olfactory lobe zinc, on the other hand, was slightly depressed. However, the levels of other metals were dependent on zinc nutriture. Zinc deficiency caused an elevation in copper concentrations in most brain parts. Restriction of food intake caused a similar increase in brain copper but generally the effect was less than with zinc deficiency. Levels of calcium, manganese, sodium and potassium, in certain brain regions, also appeared to be altered by the zinc status of an animal. Of the minerals examined, only zinc and copper displayed asymmetrical distribution between the right and left hippocampus, and severe zinc deficiency did not affect lateral distribution of these trace metals in the hippocampus. The data suggest the hypothesis that changes in brain metal content, associated with zinc deficiency, contribute to the behavioral abnormalities that occur.

Effect of dietary zinc on whole body surface loss of zinc: impact on estimation of zinc retention by balance method

Whole-body sweat losses of zinc were studied in men during three separate studies on the effects of marginal intake of zinc. Zinc lost via the sweat appeared to be directly related to dietary zinc intake. Whole body zinc losses of an average of 0.49 mg/day were observed in the men during the control period when zinc intakes averaged 8.3 mg/day. On the other hand, when zinc intakes were 3.6 mg/day, whole body surface zinc losses were substantially lower, averaging 0.24 mg/day in two of the studies and slightly lower than control values in the third study. A loss of 0.62 mg of zinc/day was observed when 33.7 mg of zinc was fed. These losses reduced apparent balances by 12 to 84% and need to be considered when evaluating zinc retention. When men were eating the diets with marginal levels of zinc (3.6 mg/day), zinc losses in sweat gradually declined with time. This suggested a homeostatic mechanism to conserve zinc during periods of depletion.

The effect of interactions between dietary egg white protein and zinc on body weight, bone growth and tissue trace metals in the 30-day-old rat

Nine groups of 30-day-old rats were fed different diets, which contained 8, 15 or 20% egg white (equivalent to 6.0, 11.3 and 15.0% protein, respectively) each at 3 levels of zinc (6, 12 and 18 ppm zinc) for 30 days. The rats consuming the 6.0% protein, regardless of zinc intake, gained less weight than the groups fed 11.3 or 15.0% protein. Plasma zinc was not influenced by dietary egg white protein content, whereas, plasma zinc levels were lower in the rats fed 6 ppm dietary zinc compared to those fed 12 or 18 ppm zinc. Of the liver trace metals measured, only iron appeared to be influenced by an egg white protein-zinc interaction. Increasing dietary egg white protein led to increased concentrations of liver zinc and magnesium. Dietary zinc levels had no effect on the concentration of these metals in the liver. Liver calcium and copper concentrations were not significantly influenced by either dietary zinc or egg white protein. Femur weights and lengths were lower in the rats fed 6.0% than in those fed 11.3 or 15.0% protein diet but were unaffected by dietary zinc. Femur width was related to dietary protein and zinc. Dietary protein and zinc were interrelated in their affect on femur zinc levels. Femur zinc concentrations increased with increasing dietary zinc levels. Also femur zinc levels decreased with increasing dietary protein content. Other femur metal (copper, iron and calcium) concentrations were higher in rats fed the low level versus the higher levels of protein, but were not influenced by dietary zinc. These results show that dietary zinc and egg white protein are interrelated with regard to their effect on body and femur growth and tissue trace metal content.

Folate status of adult males living in a metabolic unit: possible relationships with iron nutriture

Folate and iron status was monitored at monthly intervals in 40 adult males who were living in a metabolic unit for 2 to 8 months and consuming diets containing 150 to 250 micrograms of folate per day. There were significant (p less than 0.02) declines in hematocrit, serum folate, and serum ferritin. Men who participated in studies for 6 months or more or those with initial serum folate levels more than 10.5 ng/ml and erythrocyte folate levels more than 481 ng/ml also exhibited a highly significant (p less than 0.001) decline in red blood cell folate. Men with erythrocyte folate below 480 ng/ml or serum folate below 10 ng/ml and who participated in the studies for less than 5 months showed little or no change in folate status. The findings may reflect adjustments in body folate to reflect dietary intakes. Also a folate intake of 200 +/- 68 micrograms/day appeared to be adequate for maintenance of folate stores in adult males. A correlation between iron stores and folate status was also observed. However, this relationship may be coincidental.

Maximal oxygen consumption as related to magnesium, copper, and zinc nutriture

Forty-four healthy male university athletes and 20 untrained men underwent maximal treadmill exercise testing to determine the relationship between maximal oxygen consumption and various measurements of elemental nutriture. Hb and mean plasma and erythrocyte concentrations of magnesium, copper, and zinc were within established norms for both groups after a 12-h fast. Mean plasma copper concentration was significantly (p less than 0.01) higher in the athletes (90 +/- 14.3 versus 81 +/- 8.0 micrograms/dl). Average maximal oxygen consumption also was significantly (p less than 0.001) higher in the athletes [4.5 +/- 0.5 versus 3.3 +/- 0.6 L/min and 55.5 +/- 7.1 versus 47.0 +/- 6.0 ml/(kg x min)]. Plasma magnesium was significantly correlated (r = 0.46; p less than 0.002) with maximal oxygen consumption, ml/(kg x min), among the athletes. This relationship persisted when the effect of Hb concentration was removed by covariance analysis (p less than 0.005). Only a weak association (r = -0.32; p = 0.17) was found between oxygen consumption and plasma magnesium in the untrained men. We hypothesize that ionic magnesium may facilitate oxygen delivery to working muscle tissue in trained subjects.

Effect of a moderate increase in dietary protein on the retention and excretion of Ca, Cu, Fe, Mg, P, and Zn by adult males

Mineral utilization was studied by metabolic balance techniques in 10 healthy male volunteers fed diets containing 65 and 94 g protein. Both diets contained approximately 650 mg calcium, 1 mg copper, 16 mg iron, 250 mg magnesium 1000 mg phosphorus, and 7 mg zinc. The diet consisted of conventional foods; the additional 29 g protein was egg white protein mixed into a beverage and fed twice per day. Plasma mineral levels were not affected by the increase in dietary protein. When the diet provided 94 g of protein, urinary calcium and zinc were slightly, but significantly, increased by an average of 35 mg (p less than 0.05) and 0.15 mg (p less than 0.001), respectively. Apparent mineral absorption and balance were unchanged by this modest increase in dietary protein.

The effect of temporary venous occlusion on trace mineral concentrations in plasma

The effects of short-term venous occlusion on plasma concentration of trace minerals--zinc, iron, and copper--were studied in normal volunteers. In one experiment, antecubital vein blood samples were drawn simultaneously from both arms of 14 subjects while their left arms remained free and their right arms had been occluded from 60 s at 40 mm Hg pressure. Statistical comparison of paired samples showed a significant increase in zinc (p less than 0.05) and iron (p less than 0.001), but not copper concentrations in plasma from the occluded extremity. The mean increase in concentration in the right (ligated) arms with respect to the left (unligated) arms was 3.7 and 24.6%, for zinc and iron, respectively. In a second experiment, simultaneous blood samples were drawn from five subjects with neither arm occluded. No significant difference between right and left was observed. Thus, application of tourniquets during the sampling of venous blood for trace mineral analysis introduces a nonrandom factor. Standardization of sampling techniques is essential to overall reliability of trace mineral determinations.