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What happens to testosterone and estradiol levels with aging in men?
Serum total testosterone represents the unbound and protein-bound testosterone in the circulation. Most testosterone is bound to sex hormone binding globulin (SHBG) and albumin; only 2% to 4% of circulating testosterone is unbound or free. In general, serum total testosterone levels decline gradually with advancing age. Additionally, SHBG levels increase with age, resulting in an even greater relative reduction in calculated bioavailable and free testosterone with age (declines of −14.5% for total testosterone versus −27% free testosterone [FT] per decade of aging).
Hormonal Changes with Aging
| WOMEN | MEN | |
| Estradiol | ↓ | ↓ |
| Testosterone | ↓ | ↓ |
| Growth hormone | ↓ | ↓ |
| Insulin-like growth factor-1 (IGF-1) | ↓ | ↓ |
| Dehydroepiandrosterone sulfate (DHEA/S) | ↓ | ↓ |
| Thyroid-stimulating hormone (TSH) | ↑ | ↑ |
| Cortisol | ↑ | ↑ |
Although testosterone is converted to estradiol via aromatase, total serum estradiol levels in adult men do not change significantly with age. In fact, serum total estradiol levels of elderly males may be two- to fourfold higher than postmenopausal women of the same age. However, bioavailable and free estradiol levels decrease as a result of the increase in SHBG with aging (estradiol binds to SHBG with half the affinity of testosterone).
