Physiological declines in sex steroid exposure in relation to changes in body composition in healthy men-a prospective cohort study

Androgen levels decline from early adulthood and decreases are steeper in men with increasing body mass index. It is, however, unclear to what extent changes in other indices of body composition and metabolism associate with changes in sex steroid levels in healthy men. Therefore, this study investigated longitudinal changes in body composition and metabolic health in relation to sex steroid levels in healthy adult men. This is a longitudinal, population-based study. A total of 676 healthy men aged 24-46 years were measured at baseline and after ±12 years. Serum sex hormone-binding globulin (SHBG) was measured by immunoassay, testosterone (T), estradiol (E2), and dihydrotestosterone byliquid chromatography with tandem mass spectrometry (LC-MS/MS), calculated free T and calculated free E2 (cFE2), and homeostasis model assessment for insulin resistance (HOMA-IR) were calculated. Grip strength was measured by hand-grip dynamometry. Body composition was determined using dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. Mean fat mass (FM), lean mass (LM), and HOMA-IR increased (all P < .001). Decreasing androgen and SHBG levels was associated with increasing FM, whereas decreasing (cF)E2 levels were associated with decreasing FM (all P < .005). Decreasing (cF)E2 levels and increasing SHBG levels associated with decreasing LM (all P < .002). Changes in sex steroid levels and HOMA-IR or grip strength were not interrelated. Aging leads to increases in FM indices and insulin resistance, whereas changes in parameters of LM are less unequivocal. In healthy adult men, physiological changes in sex steroid exposure clearly correlate with changes in adiposity but not so with lean mass, insulin resistance, or grip strength. The SIBEX study was registered on ClinicalTrials.gov (#NVT02997033).