Requirement of zinc in human subjects.

Essentiality of zinc in nutrition of higher animals was established in 1934. Dietary zinc deficiency in humans was recognized in 1961. Dietary requirements for zinc have been estimated factorially and by balance studies. Factors that influence dietary zinc requirement include dietary and other substances that either facilitate or inhibit absorption and retention of zinc; and metabolic phenomena that influence retention or excretion of the element. These determinants must be considered in estimating the requirement and the recommended dietary allowance for this essential element. An approach that has been used to assess requirement is the measurement of dietary zinc retention by men fed diets providing sufficient energy to meet the needs of each individual and containing other nutrients in proportion to energy content. By measurement of chemical balance and subsequent analysis of the data by multiple regression, dietary factors influencing requirement have been identified and amounts of dietary zinc essential for needs calculated. Using this approach, 83% of the variance (P less than 0.0001) in requirement was accounted for by the dietary content of phosphorus and nitrogen when data from 157 twenty-eight to thirty day studies were analyzed. The equation, Intake = 1.466 + 0.23 (Zn balance) + 5.19 (P intake) + 0.40 (N intake) ? 0.30 (P intake ? 1.389) (N intake - 14.646), was used to estimate zinc requirement of persons who participated in the most recent USDA Food Consumption Survey. For all age groups, ages 9 to greater than 75y, males and females, the mean (range) difference between the estimated intakes and calculated requirements were: males 1.5% (?6.5 to + 8.1), females 11.3% (? 1.1 to + 20.3). Thus, mean intakes were generally within the 95% confidence limits of the estimated requirements. Of some interest was the finding that the mean intake of none of the groups was equivalent to the Recommended Dietary Allowance. The mean intake of males ranged from 9.32 mg in men 75y and older to 13.53 mg in persons 15–18y. The mean intake of the females ranged from 7.04 mg in women 75y and older to 9.22 mg in persons 12–14 y.     

A brief history of the influence of trace elements on brain function

From this brief review of history it is evident that lead, mercury, iodine, cobalt, iron, copper, manganese, and zinc have important influences on brain development and function. Identity of thresholds at which effects occur is needed for determination of safe and/or essential levels of these elements in diets. Such knowledge will help define human needs for essential elements, and the hazards of toxic elements.     

Adolescent pregnancy: Maternal weight effects on fetal heaviness: Possible route to improved outcomes

In a previous report of a zinc supplementation trial in pregnant adolescents zinc effect varied according to maternal weight (wt) status—normal (90–110% of expected wt), light or heavy, prompting this analysis of effects of wt status and gestational wt gain on fetal heaviness relative to length and gestational age (GA) and other pregnancy outcomes. One-third of adolescents shifted in or out of normal wt by delivery, creating seven outcome groups—light-light, light to normal, normal to light, normal-normal, normal to heavy, heavy to normal, and heavy-heavy. These wt class change groups varied significantly as to intrauterine growth (SGA, low AGA, high AGA, and LGA); by weekly grams gain per cm height (ht), birth wt, infant wt/length ratio, and occurrence of low birth wt (LBW). Infants with above average intrauterine growth had an advantage in: absolute size, length of hospital stay, rates of LBW, fetal demise, rates of low Apgar score, and other complications.This association between intrauterine growth and maternal wt class change suggests that promotion of wt gain might lower rates of LBW. Birthwt varied by quartiles of weekly wt change (gm) per cm ht in women grouped by their percent of expected wt: in the lowest quartile (Q₁) only one group in seven reached average Bwt (3025 grams); with Q₄ gain all groups did. Thus, the parameter wt gain/wk/cm ht deserves study as a tool for monitoring wt status and gain to identify those pregnant adolescents in greatest need for nutritional counseling and to set wt gain goals.Flora F. Cherry is Associate Professor of Maternal and Child Health (MCH), and Ehigie W. Ebomoyi is a post-doctoral research fellow in MCH in the Department of Applied Health Sciences; Patricio Rojas is Assistant Professor of Biostatistics; all at Tulane School of Public Health and Tropical Medicine, New Orleans, LA 70112.Harold H. Sandstead is Professor of Preventive Medicine and Community Health, University of Texas at Galveston.LuAnn K. Johnson is a biostatistician at the U.S. Department of Agriculture, Agricultural Research Service, Human Nutrition Research Center, Grand Forks, ND.Ananda R. Wickremasinghe is a fellow in the Population Genetics Program of Louisiana State University School of Medicine, New Orleans, LA.This study was funded by: (1) a U.S. Department of Agriculture, Sciences and Education Administration, Human Nutrition Extramural Research Grant to the Tulane University Medical Center; (2) a cooperative agreement (7USC, 427, 250A, 1624, 2201) between the US Department of Agriculture, Agricultural Research Services, Human Nutrition Research Center, Grand Forks, ND and Tulane Medical Center, New Orleans, LA; (3) Tulane University.     

Utility of serum ferritin as a measure of iron deficiency in normal males undergoing repetitive phlebotomy

Hematologic indices and iron balance data were obtained on 22 normal male volunteers who were subjected to a mean +/- SD phlebotomy of 164 +/- 34 ml whole blood/mo while living in a controlled environment. Over an average stay of 5 mo, volunteers did not develop anemia, but did display a reduction in iron stores that was quantitated by measurement of serum ferritin and iron balance. The percent saturation of transferrin and the usual erythrocyte parameters did not reflect changes in iron status. Loss of iron, which was calculated from quantitative phlebotomy and iron balance data, showed that a decrease of 1 ng of serum ferritin represented a loss of 4.5 +/- 5.3 mg of iron in 10 men whose initial serum ferritins were greater than 25 ng/ml, and 25.3 +/- 58.8 mg of iron in 7 men whose initial serum ferritins were less than 25 ng/ml. The period required for 3 volunteers who consumed a self-selected mixed diet at home to replace their depleted iron stores to prephlebotomy levels was about 4.5 mo. The sensitivity of serum ferritin as an index of iron stores was affirmed. In addition it was found that normal men who were consuming a mixed diet containing about 15 mg of iron daily and losing blood at a rate of 164 +/- 34 ml/mo did not increase their iron absorption sufficiently to compensate for the iron loss.     

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.