Objective: The metabolic and genetic correlates of circulating insulin-like growth factor-1 (IGF-1) and its main circulating carrier, IGF-1-binding-protein-3 (IGFBP-3), are unclear.
Methods and results: We measured serum IGF-1 and IGFBP-3 concentrations in a sample of the Framingham Heart Study (N=3977, aged 40+/-9 years, 46% male) and evaluated their relations to cardiovascular risk factors using multivariable regression. Serum IGF-1 was inversely correlated with age, body mass index, total cholesterol, the presence of diabetes, alcohol consumption, and glomerular filtration rate (all P<0.01), whereas the ratio of IGF-1:IGFBP-3 was lower in women and inversely related to age, triglycerides, high-density lipoprotein cholesterol, systolic blood pressure, and alcohol consumption (all P<0.0001). Circulating IGF-1 correlated negatively with insulin resistance (homeostatic model assessment) (r=-0.1; P<0.0001) and was lower in participants with more components of the metabolic syndrome (Adult Treatment Panel III criteria) (P<0.0001). Additive genetic factors (heritability) accounted for 43% and 39% of the variation of IGF-1 and IGFBP-3, respectively (both P<10(-27)).
Conclusions: Our cross-sectional observations in a large community-based sample link lower circulating IGF-1 to greater metabolic risk burden and underscore substantial genetic influences on IGF-1 concentrations. Prospective studies are warranted to elucidate whether lower IGF-1 concentrations predict greater metabolic risk longitudinally.