Background: Endogenous and exogenous sex hormones affect changes in body composition during aging via independent and dependent effects on the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and associated binding proteins (BP).
Methods: Fasting serum IGF-1, IGFBP3, testosterone, estrone, and sex hormone binding globulin were analyzed in 48 women on hormone replacement (HRT) (unopposed oral estrogen, HRT+, 74.0 +/- 6 years), 135 women not on HRT (HRT-, 77.3 +/- 7 years), and 128 healthy men (men, ). Total lean body mass (LBM) and total fat were measured by dual energy X-ray absorptiometry.
Results: Total LBM decreased with age in all groups (p = .05). LBM was greater, and IGF-1, IGFBP3, and testosterone were lower in HRT+ versus HRT- women (p = .02, p = .01, p = .04, and, respectively). LBM in men was positively related to IGF-1 (p = .02) and testosterone (p < .01), whereas LBM was associated with IGFBP3 (p = .04) and total fat (p < .001) in female HRT+ and total fat (p < .01) in HRT- women. IGF-1 decreased with age in men and HRT- women (p < .01) but did not decrease in HRT+ women. Total fat significantly decreased across age (p < .05). Controlling for age and HRT, the rate of decrease in fat was slower in men versus women (p = .02). IGFBP3 decreased in all groups across age (p < .01), and the ratio of IGF-1 to IGFBP3 decreased faster in men compared to HRT+ and HRT- women (p = .02).
Conclusions: Our data indicate divergent influences of sex steroids, IGF-1, and IGFBP3 on age-related changes in LBM in healthy elderly men and women.