Age-related changes of serum sex hormones, insulin-like growth factor-1 and sex-hormone binding globulin levels in men: cross-sectional data from a healthy male cohort

OBJECTIVE The age-dependent decline of the gonadal and somatotopic axis has been causally linked to frailty in the elderly by their effects on muscle mass and bone mineral density. However, for healthy men data on serum oestr ogens and androgens, as well as IGF-1, as a common outcome measure covering the whole adult age range are scarce. We therefore studied healthy, nonobe se male subjects between 20 and 80 years of age to asses their morning conc entrations of total (T), free (FT), bioavailable testosterone (bT), oestrad iol (E2), bioavailable oestradiol (bE2), oestrone (E1), sex-hormone binding globulin (SHBG), and insulin-like growth factor 1 (IGF-1). SUBJECTS AND MEASUREMENTS Five hundred and seventy-two male healthy volunte ers with a BMI < 30 kg/m(2) recruited from regular blood donors and senior sports clubs participated in the study. Serum samples were obtained during morning hours and T, FT, E2, E1, SHBG, albumin and IGF-1 were measured by r adio-immunoassay systems. In addition, bT and bE2 were calculated. A potent ial relationship between sex hormones and IGF-1 was tested by multiple regr ession analysis including age and BMI. RESULTS Ageing was negatively related to serum levels of sex steroids and I GF-1 (both P < 0.0001) with a mean decrease (youngest vs. oldest) of 51% fo r T, 64% for FT, 78% for bT, 32% for E2, 62% for bE2, 29% for E1 and 51% fo r IGF-1 starting in early adulthood whereas SHBG increased after the 5th de cade of life (ANOVA P < 0.001). The decline of sex hormones and IGF-1 remai ned relatively unchanged after adjustment for BMI. Multiple regression anal ysis revealed an age-and BMI- independent association between oestradiol an d IGF-1. CONCLUSIONS In contrast to the female situation sex hormones in healthy, no nobese men decline continuously with age. This process has already started in the third decade, and is paralleled by a decline of IGF-1 serum levels l eading to a substantial proportion of elderly men with markedly lowered ser um levels of bioavailable sex hormones and IGF-1 compared to the young adul t male range. With the recent demonstration of beneficial effects of androg en replacement therapy in healthy males on general well being, muscle mass and bone mineral density the present data may underline the importance of m ore detailed studies on the biological significance of hormonal changes in men with age.