SEX-DIFFERENCES IN THE CONTROL OF SEX-HORMONE-BUILDING GLOBULIN IN THE ELDERLY - ROLE OF INSULIN-LIKE GROWTH-FACTOR-I AND INSULIN

Objective: Serum levels of sex-hormone-binding globulin (SHBG) have be en reported in the literature to increase with age in both sexes. We h ave investigated the variations in levels of androgens, insulin and IG F-I with age and have evaluated their putative roles to obtain a bette r understanding of the increase in SHBG. Design: Cross-sectional pilot study of blood samples in healthy elderly subjects aged 50 to 90 year s. Patients and Methods: Forty-four postmenopausal women and 40 men we re classified into three age groups. Subjects who were obese, undernou rished or smokers and postmenopausal women receiving hormone replaceme nt therapy were excluded from the study Body mass index and waist/hip ratio were evaluated in each subject. Fasting levels of blood glucose, insulin, triglycerides, cholesterol, SHBG, testosterone, dehydroepian drosterone sulfate (DHEAS) and IGF-I were measured. Free testosterone and glucose/insulin ratio were calculated. Results: The results are ba sed on variance analysis of the mean of each parameter in the three ag e groups. Multiple regression analysis was performed to define the rol e of age, insulin and IGF-I in the increase in SHBG. The increase in S HBG with age in older men was significant but that in postmenopausal w omen was not. Decreasing DHEAS with age was confirmed. No significant variations in glucose and insulin were observed with age in our select ed population. A positive correlation was observed between insulin and triglycerides in elderly men and women, IGF-I decreased significant w ith age in both sexes. Insulin was the main factor explaining SHBG inc rease with age in women. In men, both age and IGF-I contributed to the SHBG increase. Conclusions: The factors regulating the increase in SH BG with age appear to be different in the two sexes. Insulin plays a m ajor role in women, whereas a decrease in IGF-I is the predominant reg ulating factor in men. These results should be thought of as a working hypothesis rather than a reflection of physiology.