A cross-sectional study of IGF-1 determinants in women

Evidence is accumulating that elevated circulating insulin-like growth fact or I (IGF-I) is related to increased cancer risk. The identification of hor monal, reproductive and lifestyle characteristics influencing its synthesis and bioavailability is of particular interest. Data from 400 women, who se rved as controls in two case-control studies nested within the same prospec tive cohort study, were combined. IGF-I, IGF-binding proteins 1, 2 and 3 (I GFBP-1, -2, -3) and insulin were measured in serum samples from all subject s and cotinine in 186 samples. Age appears to be the most important determi nant of total IGF-I levels in women. Anthropometric measures, such as body mass index (BMI) or waist-to-hip ratio (WHR) do not seem to influence total IGF-I concentrations in peripheral blood, but may modulate IGF-I bioavaila bility through insulin-dependent changes in IGFBP-1 and -2 concentrations. Age at menarche, phase of the menstrual cycle at blood draw, parity, menopa use, past oral contraceptive or hormone replacement therapy use, and tobacc o smoking do not appear to exert an independent effect on IGF-I and its bin ding proteins. There was some suggestion that regular physical activity may increase total IGF-I and that women with positive family history of breast cancer might have higher IGF-I levels than those without such diagnosis in their relatives. (C) 2001 Lippincott Williams & Wilkins.