Insulin-like growth factor I (IGF-I) is a critical factor in the regulation of various physiologic effects, including bone formation and protein metabolism. Nutrient intake is a main regulator of circulating IGF-I. The relation of zinc status and IGF-I in adulthood has not been studied adequately even though suboptimal intakes of zinc are reported widely in the elderly. This study examined the relation between calculated nutrient intakes from 119 postmenopausal women and concentrations of IGF-I and IGF binding proteins (IGFBPs). Dietary intake was evaluated by 4-d weighed diet records at baseline and 2 y. Mean intakes of 25 nutrients were calculated. Concentrations of IGF-I and IGFBPs were measured by radioimmunoassays at baseline and 2 y. Mean age (63 +/- 4 y), weight (66 +/- 9 kg), and nutrient intake were correlated with the mean IGF-I concentration at baseline (172 +/- 57 microg/L) and 2 y (142 +/- 43 microg/L). IGF-I concentrations were significantly correlated with mean protein and zinc intake at baseline (r = 0.313, P = 0.001; r = 0.298, P = 0.001, respectively) and 2 y (r = 0.256, P = 0.008; r = 0.331, P = 0.001, respectively). After age, weight, and other nutrient intakes were adjusted for in multiple regression at baseline and 2 y, zinc remained the major determinant of IGF-I concentrations. These results suggest that low zinc intake is associated with low IGF-I concentrations in healthy postmenopausal women and that the effects of zinc may be independent of protein intake.