CohortHumann = 8902001
Longitudinal effects of aging on serum total and free testosterone levels in healthy men. Baltimore Longitudinal Study of Aging.
Plain-language summary
This study set out to track how testosterone changes as men age, and whether the change is aging itself or the illnesses and medications that come with it. It measured total testosterone and SHBG (sex hormone-binding globulin, a protein that binds testosterone and holds it out of use, so a higher level leaves less testosterone free and usable) in 890 healthy men repeatedly over time, adjusting for body mass and medication use. Both total and free testosterone declined steadily with age, and the decline held independently of health problems. By age 60 about 20% of men had testosterone low enough to meet the criteria for hypogonadism (when the testicles do not make enough testosterone), rising to 50% by age 80.
Key findings
- Total testosterone and free testosterone (calculated as total testosterone divided by SHBG) declined steadily with age, independent of health factors.
- Body mass index was linked to lower total testosterone but not free testosterone.
- Beta-blocker use was linked to higher total and free testosterone levels.
- The percentage of men with hypogonadal testosterone levels increased with age: 20% over 60, 30% over 70, and 50% over 80.
How to analyze the study yourself
- Study type
- Cohort studies track the same group over time, which helps spot trends, but they cannot prove cause and effect because other unmeasured factors might influence the results.
- Population
- Healthy men in the Baltimore Longitudinal Study on Aging.
- Funding
- Not reported
- Takeaway
- This study found that testosterone levels decline steadily with age, and by 80, half of men meet the threshold for low testosterone. If you're over 60 and noticing symptoms like low energy or reduced muscle mass, it may be worth checking your testosterone levels.