Relationship between plasma insulin-like growth factor I (IGF-I) levels and body mass index (BMI) in adults.

We investigated the relationship between plasma insulin-like growth factor I (IGF-I) levels and the body mass index (BMI) in 558 healthy adults (238 males and 320 females), aged 21-80 yrs. The subjects were divided into three groups based on the BMI: 1) underweight group (BMI < 20, n = 145), 2) normal group (BMI 20-25, n = 179) and 3) overweight group (BMI > 25, n = 234). Blood samples were obtained after overnight fasting and plasma IGF-I concentrations were measured by specific radioimmunoassay after acid-ethanol extraction. Plasma IGF-I levels declined with age in each group and the regression lines were parallel. In both sexes of each decade, mean plasma IGF-I values were lower in the underweight and overweight groups than in the normal group. Age- and sex-matched analysis revealed that plasma IGF-I values were positively correlated with BMI under 25, whereas plasma IGF-I was reversely correlated with BMI beyond 27. These findings suggest that the plasma IGF-I levels are influenced by body composition independently of aging in adults, aged 21-80 yrs.