Assessing the Relationship between Serum IGF-1 and BMI by Age in the Long Life Family Study

Background Serum levels of insulin-like growth factor 1 (IGF-1) and body mass index (BMI) are both associated with susceptibility to age-related diseases. Reports on the correlation between them have been conflicting, with both positive to negative correlations reported. However, the age ranges of the participants varied widely among these studies. Methods Using data on 4,241 participants (aged 24–110) from the Long Life Family Study, we investigated the relationship between IGF-1 and BMI by age groups using regression analysis. Results When stratified by age quartile, the correlation between IGF-1 and BMI varied: in the 1st quartile (Q1, 24 y–58 y) the correlation was negative ( r = −0.1, P = 0.0008); in Q2 (59 y– 66 y) it was negative ( r = −0.035) but non-significant; in Q3 (67 y–86 y) it was positive ( r = 0.045) but non-significant; and in Q4 (87 y–110 y) the correlation was positive ( r = 0.14, P < 0.0001). This pattern did not differ by sex. We observed a similar age-related pattern between IGF-1 and BMI among participants in the third National Health and Nutritional Examination Survey. Conclusions Our results, that the relationship between IGF-1 and BMI differs by age, may explain some of the inconsistency in reports about their relationship and encourage additional studies to understand the mechanisms underlying it.