Zinc deficiency, chronic starvation and hypothalamic-pituitary-thyroid function

and Jerome M. Hershman ABSTRACT Male Sprague-Dawley rats were fed a zinc-deficient diet to study its effects on the hypothalamic-pituitary-thyroid axis. As zinc-deficient animals fail to gain weight, they were compared to pair-fed growth restricted animals as well as ad libitum fed controls. The growth velocity curves were superimposable for the zinc-deficient animals and the pair-fed controls; both were markedly reduced compared to the ad libitum controls. Both the zinc-deficient and the pair-fed controls had lower triiodothyronine (T:t) and thyroxine levels compared to the ad libitum controls. In addition T3 values were lower in the zinc-deficient animals compared to the pair-fed controls (P < 0.05). Hypothalamic thyrotrophin-releasing hormone content was decreased in the zinc-deficient rats (162 ± 32 pg/ml) compared to the ad libitum controls (305 ± 102; P < 0.01). The 1251 thyroidal uptakes were not significantly different between the zinc-deficient and the pair-fed controls. Zinc deficiency lowers T:, more than comparable caloric restriction; this suggests that zinc deficiency may impair extrathyroidal production ofT:1. Am. J. C/in. Nutr. 33: 1767-1770, 1980. Zinc recently achieved the status of a mi-cronutrient of established importance in hu-man nutrition and medicine. Although a bi-ological role for zinc was first recognized more than 100 years ago, the first cases of human zinc deficiency were not described until the early 1960’s. Features of nutritional zinc deficiency in animals and man include anorexia, growth retardation, impaired kera-togenesis, skin lesions, hypogonadism, hypo-geusia, lethargy, behavioral changes, in-creased susceptibility to infection and possi-bly, impaired development of the immune system (1-3). Morley et al. (4) have shown that vitamin A deficiency produces biochemical hyperthy-roidism. As zinc deficiency alters vitamin A metabolism (5), we believed it would be of interest to study the effects of zinc deficiency on thyroid function. We could fmd no liter-ature on the effects of zinc on thyroid func-tion. Method