Changes in insulin‐like growth factor‐I and ‐II associated with fat but not lean mass in early old age

OBJECTIVE: To test the hypothesis that insulin‐like growth factors‐I and II (IGF‐I and II) decline during late midlife and that greater declines are related to higher fat mass and lower lean mass. METHODS: A total of 1,542 men and women in a British birth cohort study had IGF‐I and II measured by immunoassay of blood samples at age 53 and/or 60‐64 years. Fat mass, android:gynoid fat ratio, and appendicular lean mass were measured at 60‐64 years using dual‐energy X‐ray absorptiometry (DXA). Associations between changes in IGF‐I or II and body composition outcomes were examined using conditional change linear regression models. RESULTS: Mean IGF‐I and IGF‐II concentrations were lower at 60‐64 than at 53 years, by 12.8% for IGF‐I and by 12.5% for IGF‐II. Larger declines in either IGF‐I or II were associated with higher fat mass at 60‐64 years. Although higher IGF‐I at 53 years was associated with higher lean mass, there was little evidence linking changes in IGF‐I or II to lean mass. CONCLUSIONS: The findings suggest that IGF‐I and II concentrations decline with age, and greater declines are associated with higher fat mass levels. These results provide some evidence for the suggested roles of IGF‐I and II in regulating fat mass but not lean mass in older age.