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.
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.
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