DECLINE IN SOMATOMEDIN-C (INSULIN-LIKE GROWTH FACTOR-I) WITH EXPERIMENTALLY INDUCED ZINC-DEFICIENCY IN HUMAN-SUBJECTS

Six healthy volunteers (5 males and 1 female) participated in this study which was designed so that each subject served as his/her own control. During a 4-week stabilisation period subjects consumed a zinc-deficient diet (1.28 mg Zn/day) and zinc supplement (Zn-acetate in capsules) so that their daily intake of zinc was equivalent to their daily habitual intake prior to study period. The stabilisation period was followed by a 12-week zinc-depletion period where subjects consumed the zinc-deficient diet with no zinc supplement. Levels of energy, protein and all other nutrients were kept constant throughout the study period and matched their intake prior to the initiation of the study. Body weight and parametric measurements of zinc status indicated that zinc deficiency has been produced in these subjects. Plasma somatomedin-C/insulin-like growth factor 1 (IGF-1) dropped significantly (p < 0.05) at the first month of zinc-depletion and continued to decline throughout the second and third month (p < 0.001). The pattern of decline in plasma IGF-1 was comparable to the decline in body weight and plasma zinc concentration. The present study suggests that IGF-1 is zinc-dependent and could be used as a valid parameter for diagnosing zinc-deficiency. I suggest that the present finding should be considered in the interpretation of studies dealing with growth retardation associated with zinc deficiency in humans.