Testosterone levels in men typically begin declining around age 30 to 40, dropping roughly 1% per year after that point. The decline is gradual enough that most men retain normal levels well into older age, but certain health factors can accelerate the process significantly.
When the Decline Starts
Testosterone production peaks during late adolescence and early adulthood, then holds relatively steady through the 20s. The downward trend begins somewhere in the late 30s to early 40s, depending on the individual. The Mayo Clinic places the typical onset at around age 40, while Cleveland Clinic notes levels can start dropping as early as the late 30s. Either way, the change is subtle at first: about 1% per year.
That 1% annual figure is an average across the population. Some men decline faster, others barely at all. A man with a total testosterone level of 600 ng/dL at age 40 might expect to be around 540 ng/dL by age 50 and roughly 480 ng/dL by age 60, assuming a steady 1% annual drop. Most older men still fall within the normal range despite decades of gradual decline.
Why Testosterone Drops With Age
The cells responsible for making testosterone, called Leydig cells, sit inside the testes and respond to a hormone signal (LH) sent from the brain’s pituitary gland. As men age, these cells become less responsive to that signal. The number of receptor sites on Leydig cells decreases, and two key steps in the testosterone production chain become less efficient: the initial cellular signaling triggered by LH and the transport of cholesterol (the raw material for testosterone) into the part of the cell where it gets converted.
Oxidative stress, the gradual accumulation of cellular damage from reactive molecules, appears to play a central role in this breakdown. Inflammation-related pathways also contribute. In animal studies, blocking certain inflammatory enzymes partially reversed age-related testosterone drops, suggesting that chronic low-grade inflammation accelerates the decline.
Notably, the brain’s signaling system doesn’t seem to be the primary problem. LH levels in aging men tend to stay the same or even increase, which means the brain is still sending the “make more testosterone” message. The Leydig cells just respond less and less effectively over time.
Total vs. Free Testosterone
Your body carries testosterone in two forms. Most of it is bound to proteins in the blood, primarily one called SHBG (sex hormone-binding globulin). Only the unbound portion, called free testosterone, is readily available for your tissues to use. When SHBG levels are high, more testosterone is locked up and unavailable, even if your total number looks adequate on a blood test.
SHBG levels can shift with age and various health conditions. If your SHBG is elevated, you could have a normal-looking total testosterone reading while your body is actually running low on usable testosterone. This is one reason a single blood test doesn’t always tell the full story, and why some doctors check free testosterone or SHBG alongside the total number.
How the Decline Shows Up
The most telling symptoms are sexual: reduced sex drive, fewer spontaneous or morning erections, and difficulty maintaining erections. These tend to be the earliest and most specific signs that testosterone has dropped meaningfully.
Beyond sexual function, low testosterone can cause a cluster of changes that are easy to attribute to “just getting older”:
- Body composition shifts: increased body fat, decreased muscle mass and strength, reduced endurance
- Mood and cognition: depressed mood, difficulty concentrating, memory issues
- Physical changes: loss of body hair, hot flashes, enlarged breast tissue
Many of these symptoms overlap with other conditions like depression, sleep apnea, and thyroid problems, which is why a clinical diagnosis requires both symptoms and confirmed low blood levels, not just one or the other.
How Low Testosterone Is Diagnosed
The American Urological Association defines low testosterone as a total level below 300 ng/dL. But a single test isn’t enough. The guidelines require two separate blood draws, both taken in the early morning when testosterone naturally peaks. Levels fluctuate throughout the day and can be temporarily suppressed by poor sleep, illness, or stress, so the two-test requirement helps avoid a false diagnosis.
Crucially, a number below 300 ng/dL alone doesn’t automatically mean you need treatment. The clinical diagnosis requires low levels combined with symptoms. Some men function fine at levels that would cause significant problems in others.
Obesity and Health Accelerate the Drop
While aging accounts for a slow, steady decline, body weight and overall health can have a much larger impact. A Harvard-cited study of over 1,600 men found that each single-point increase in BMI was linked to a 2% decrease in testosterone. To put that in perspective: gaining enough weight to raise your BMI by five points could suppress testosterone by roughly 10%, the equivalent of a decade of normal aging compressed into a weight change.
Waist circumference may matter even more than overall weight. A study of over 1,800 men found that a four-inch increase in waist size raised the odds of having low testosterone by 75%. Ten years of aging, by comparison, increased those odds by only 36%. This means a 35-year-old man carrying significant abdominal fat could have testosterone levels typical of a much older, leaner man.
Type 2 diabetes, metabolic syndrome, and other chronic conditions further compound the decline. For many men, the most effective way to protect testosterone levels isn’t a prescription but maintaining a healthy weight, staying physically active, and managing conditions that drive chronic inflammation.