Bioavailable insulin-like growth factor-i inversely related to weight gain in postmenopausal women regardless of exogenous estrogen

Background: Weight gain, insulin-like growth factor-I (IGF-I) levels, and excess exogenous steroid hormone use are putative cancer risk factors, yet their interconnected pathways have not been fully characterized. This cross-sectional study investigated the relationship between plasma IGF-I levels and weight gain according to body mass index (BMI), leptin levels, and exogenous estrogen use among postmenopausal women. Methods: This study included 794 postmenopausal women who enrolled in an ancillary study of the Women's Health Initiative Observational Study between February 1995 and July 1998. The relationship between IGF-I levels and weight gain was analyzed using ordinal logistic regression. We used the molar ratio of IGF-I to IGF binding protein-3 (IGF-I/IGFBP-3) or circulating IGF-I levels adjusting for IGFBP-3 as a proxy of bioavailable IGF-I. The plasma concentrations were expressed as quartiles. Results: Among the obese group, women in the third quartile (Q3) of IGF-I and highest quartile of IGF-I/ IGFBP-3 were less likely to gain weight (>3%from baseline) than werewomenin the first quartiles (Q1).Among the normal-weight group, women in Q2 and Q3 of IGF-I/IGFBP-3 were 70% less likely than those in Q1 to gain weight. Among current estrogen users, Q3 of IGF-I/IGFBP-3 had 0.5 times the odds of gaining weight than Q1. Conclusions: Bioavailable IGF-I levels were inversely related to weight gain overall. Impact: Although weight gain was not consistent with increases in IGF-I levels among postmenopausal womenin this report, avoidance of weight gain as a strategy to reduce cancer risk maybe recommended.