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.

History of zinc as related to brain function.

Zinc (Zn) is essential for synthesis of coenzymes that mediate biogenic-amine synthesis and metabolism. Zn from vesicles in presynaptic terminals of certain glutaminergic neurons modulates postsynaptic N-methyl-D-aspartate (NMDA) receptors for glutamate. Large amounts of Zn released from vesicles by seizures or ischemia can kill postsynaptic neurons. Acute Zn deficiency impairs brain function of experimental animals and humans. Zn deficiency in experimental animals during early brain development causes malformations, whereas deficiency later in brain development causes microscopic abnormalities and impairs subsequent function. A limited number of studies suggest that similar phenomena can occur in humans.

Causes of iron and zinc deficiencies and their effects on brain.

Low consumption of foods rich in bioavailable iron (Fe) and zinc (Zn) such as meat, particularly red meat, and high consumption of foods rich in inhibitors of Fe and Zn absorption, such as phytate, certain dietary fibers and calcium, cause Fe and Zn deficiencies. Neuropsychologic impairment is one of several potential outcomes of these deficiencies.

Polyatomics in zinc isotope ratio analysis of plasma samples by inductively coupled plasma-mass spectrometry and applicability of nonextracted samples for zinc kinetics.

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful tool for both quantitative multielement analyses of inorganic elements and measurement of isotope ratios (IRs). The main disadvantage of this technique is the existence of polyatomic isobaric interferences at some key masses. Zinc has been investigated for such potential interferences in serum or plasma. The Zn isotopes, 66Zn and 68Zn, have no apparent interferences, but 32S1602 and 32S2 are isobaric with 64Zn. The possible effects of S and other major components of blood plasma-Na, K, Cl, P, Ca-on Zn IRs were investigated using a series of mineral solutions which simulated human plasma with respect to these elements. The mixture of all mineral elements interfered only with 64Zn (6.66 ng/mL) and 70Zn (8.51 ng/mL). Interferences to 66Zn, 67Zn, and 68Zn were minimal containing 0.90, 0.94, and 0.39 ng/mL, respectively. The copresence of Na or S shifted 35Cl16O2 (atomic mass 67 coming from Cl solution) to 35Cl2 which reduced the contribution to 67Zn. The hypothesis that Zn IRs obtained from plasma at various intervals after the intravenous administration of enriched 67Zn to humans would reflect those obtained after extraction of Zn was therefore tested. To compare the two pretreatment methods, "extraction" versus "nonextraction," specimens were collected from 10 human subjects at intervals of 5 min to 24 h postinjection, and in 4 subjects from 5 min to 9 d postinjection. Two separate aliquots of plasma from each time-point were dried and digested with hydrogen peroxide, and the residue dissolved in nitric acid. One specimen was subjected to zinc extraction using ammonium diethyldithiocarbamate chelate followed by back extraction into nitric acid. The matching aliquot received no further pretreatment. The normalized IRs obtained from 67Zn/66Zn and 67Zn/68Zn in both the "extracted" and "nonextracted" samples agreed well (r2 = 0.976 and r2 = 0.985, respectively) compared to those from other ratios (r2 = 0.838 for 67Zn/64Zn and r2 = 0.747 for 67Zn/70Zn). Considering the minimum possibility of isobaric interferences in plasma samples, 67Zn/68Zn obtained from "nonextracted" samples is sufficient for routine Zn kinetic analysis by ICP-MS.

Effects of repletion with zinc and other micronutrients on neuropsychologic performance and growth of Chinese children.

The knowledge that zinc is essential for growth and neuropsychologic performance and a report of zinc-responsive stunting in Chinese children prompted this project. This article summarizes findings from a 10-wk, double-blind, controlled trial of zinc repletion in 740 urban, 6-9-y-old first graders from low-income families in Chongqing, Qingdao, and Shanghai, People's Republic of China. Treatments were 20 mg Zn alone (Z), 20 mg Zn with micronutrients (ZM), and micronutrients alone (M). The M mixture was based on National Research Council guidelines. Nutrients that might interfere with zinc retention were excluded or given in lower amounts. Main outcomes were changes in neuropsychologic performance and knee height. Hemoglobin, serum ferritin, plasma and hair zinc, and whole blood and hair lead were also measured. Anemia was not common, and serum ferritin concentrations were usually within the range of normal. Mean baseline plasma zinc concentrations were marginal in children from Chongqing and Qingdao and normal in children from Shanghai. After treatment with ZM or M plasma zinc increased. Hair zinc tended to decrease after all treatments. Mean baseline whole blood lead concentrations were slightly below the limit considered excessive for children by the US Centers for Disease Control and Prevention. Neuropsychologic performance and growth were most improved after treatment with ZM. These findings were consistent with the presence of zinc and other micronutrient deficiencies.

A preliminary report: effects of zinc and micronutrient repletion on growth and neuropsychological function of urban Chinese children.

OBJECTIVE: Zinc is essential for growth and cognition of experimental animals. Past research found zinc repletion improved growth of stunted Chinese children. Therefore we measured effects of zinc repletion on growth and neuropsychological functions of children. DESIGN: Double-blind randomized controlled treatment trial. SETTING: Elementary schools in low income districts of Chongqing, Qingdao and Shanghai. SUBJECTS: Three hundred-seventy-two 6 to 9 year old first graders. INTERVENTIONS: Treatments were 20 mg zinc, 20 mg zinc with micronutrients, or micronutrients alone. The micronutrient mixture was based on guidelines of the US NAS/NRC. Treatments were assigned to classrooms of 40 or more children each, and administered by teachers 6 days per week for 10 weeks. MEASURES OF OUTCOME: Changes in knee height and neuropsychological functions. RESULTS: Zinc alone had the least effect on growth while zinc with micronutrients had the largest effect; micronutrients alone had an intermediate effect. Zinc-containing treatments improved neuropsychological functions, but micronutrients alone had little effect. CONCLUSIONS: The findings confirm the essentiality of zinc for growth of children, and show, for the first time, the essentiality of zinc for neuropsychological functions of children. In addition, the need for repletion of other potentially limiting nutrients in studies examining the effects of specific nutrients on growth and neuropsychological functions was confirmed.

Deliberations and evaluations of approaches, endpoints and paradigms for determining zinc dietary recommendations.

The work group considered past and future Recommended Dietary Allowances (RDAs) for zinc. Past RDAs were based in large part on metabolic balance data. Balance measurements are technically difficult and it is uncertain that they reflect true requirements. Therefore other methods should be used to determine requirements and the RDA. The best approach at this time is the factorial method. In the future, data from measurements of zinc kinetics, in relation to diet and physiological functions will provide useful insights. Future RDAs should provide for at least three levels of bioavailability: low, moderate and high. Whether adjustments should be made in the RDA to account for life style factors is a matter of philosophy. The importance of the differences (gaps) between the RDA and usual intakes of zinc by persons who are apparently in good health, or between the RDA and other dietary guidelines, is an issue for consideration.

Requirements and toxicity of essential trace elements, illustrated by zinc and copper.

Early signs of toxicity of essential trace elements are important. Some trace elements are available over-the-counter (OTC) and/or are present at industrial waste sites. Physicochemically similar trace elements compete for ligands, impairing functions, which is exemplified by the zinc-copper antagonism described long ago by Van Campen, Hill and Matrone, and Klevay. Intestinal absorption of copper is inhibited by zinc. Thus risk of copper deficiency is increased when the molar ratio of zinc to copper (Zn:Cu) is high. As shown by experiments, copper deficiency can occur in humans. Manifestations include decreased erythrocyte copper-zinc superoxide dismutase, increased low-density-lipoprotein cholesterol, decreased high-density-lipoprotein cholesterol, decreased glucose clearance, decreased methionine and leucine enkephalins, and abnormal cardiac function. Calculation of a preliminary reference dose for OTC zinc that assumed high bioavailability and uncertain copper intakes established 9 mg as a safe amount for 60-kg adults.

Is zinc deficiency a public health problem?

Zinc is essential for all species. Human zinc deficiency related to diet was recognized 30 yr ago among adolescents in Iran and Egypt. Subsequent factorial calculations, balance studies, and tracer studies of bioavailability and turnover established the amounts of zinc needed for equilibrium and dietary factors that impair retention. Comparison of dietary intakes of zinc with requirements suggested many women and children are at risk of deficiency. Epidemiological studies associated low plasma levels of zinc with abnormal pregnancy outcomes and controlled intervention trials showed that zinc repletion improved pregnancy outcomes. Low iron nutriture, a common phenomenon in women, was shown to be associated with low zinc nutriture. Thus the hypothesis that zinc deficiency is a public health problem appears to be true.

Iron and zinc nutriture of premenopausal women: associations of diet with serum ferritin and plasma zinc disappearance and of serum ferritin with plasma zinc and plasma zinc disappearance.

The Second National Health and Nutrition Examination Survey found low iron and zinc intakes and low serum ferritin in many premenopausal women. Therefore food frequency history, serum ferritin, plasma zinc, plasma zinc disappearance, and zinc turnover rate were measured in healthy premenopausal women. Plasma zinc disappearance and turnover rate were determined by inductively coupled plasma mass spectroscopic analysis of the plasma ratio of zinc 67 to zinc 68 before and 30 to 60 minutes after intravenous injection of 67Zn. Food frequency predicted serum ferritin concentration in 38 women and plasma zinc disappearance in 19. Frequent red meat intake was associated with higher serum ferritin concentration and a "normal" plasma zinc disappearance. Frequent milk intake was associated with lower serum ferritin concentration and a rapid plasma zinc disappearance. After exclusion of an outlier, in 18 women serum ferritin concentrations were lower when plasma zinc was < 70 micrograms/dl (p < 0.03), and plasma zinc disappearance and turnover rate were higher when serum ferritin was < 20 ng/ml (p < 0.05). Serum ferritin concentration and plasma zinc disappearance constant were inversely and nonlinearly related (R2 = 0.777, p = 0.0003). These findings suggest that avoidance of red meat increases the risk of iron and zinc deficiencies, and low serum ferritin concentrations suggest the possibility of low zinc nutriture.

Understanding zinc: recent observations and interpretations.

Zinc plays a key role in genetic expression, cell division, and growth and is essential for function of more than 200 enzymes. Effects of deficiency include stunting, anergy, dermatitis, poor healing, teratology, and neuropsychologic impairments. Risk of deficiency is related to level of anabolism and food choice. Bioavailability is greater from flesh foods than foods of plant origin. Pharmacologic intakes of zinc lower copper retention and impair copper-dependent processes. Pharmacologic intakes of folate impair zinc metabolism and may cause abnormal pregnancy outcomes. A recent review suggests zinc deficiency is common among populations of developing countries, particularly those that are deficient in iron.

Zinc: health effects and research priorities for the 1990s.

This review critically summarizes the literature on the spectrum of health effects of zinc status, ranging from symptoms of zinc deficiency to excess exposure. Studies on zinc intake are reviewed in relation to optimum requirements as a function of age and sex. Current knowledge on the biochemical properties of zinc which are critical to the essential role of this metal in biological systems is summarized. Dietary and physiological factors influencing the bioavailability and utilization of zinc are considered with special attention to interactions with iron and copper status. The effects of zinc deficiency and toxicity are reviewed with respect to specific organs, immunological and reproductive function, and genotoxicity and carcinogenicity. Finally, key questions are identified where research is needed, such as the risks to human health of altered environmental distribution of zinc, assessment of zinc status in humans, effects of zinc status in relation to other essential metals on immune function, reproduction, neurological function, and the cardiovascular system, and mechanistic studies to further elucidate the biological effects of zinc at the molecular level.