Low testosterone happens when the body either can’t produce enough of the hormone or doesn’t receive the right signals to make it. The American Urological Association defines low testosterone as a total level below 300 ng/dL. The causes range from natural aging to obesity, chronic disease, medications, genetic conditions, and even environmental chemicals. Most cases involve more than one contributing factor working together.
How Testosterone Production Works
Understanding what goes wrong starts with understanding the normal process. Your brain and your testes work as a team. The hypothalamus, a small region deep in the brain, releases a signaling hormone that tells the pituitary gland to produce two key hormones. One of those, luteinizing hormone, travels through the bloodstream to the testes and triggers testosterone production. A break anywhere in this chain means less testosterone reaches your body.
When the problem originates in the testes themselves, it’s called primary hypogonadism. The signal from the brain arrives, but the testes can’t respond properly. When the problem starts in the brain, either in the hypothalamus or pituitary gland, it’s called secondary hypogonadism. The testes could work fine, but they never get the message to start producing. This distinction matters because the cause determines what kind of treatment, if any, is appropriate.
Aging and the Gradual Decline
Testosterone levels peak in early adulthood and then slowly drop. In men between 40 and 70, total testosterone decreases at roughly 0.4% per year. Free testosterone, the portion that’s actively available to your tissues, drops faster at about 1.3% per year. That difference matters because free testosterone is what your body actually uses.
This gradual decline is a normal part of aging, not a disease. Many men maintain levels well above 300 ng/dL into their 70s and beyond. But for others, especially those with additional risk factors like obesity or chronic illness, the age-related slide can push levels below that threshold and start causing noticeable symptoms like fatigue, reduced muscle mass, and low sex drive.
Obesity and the Estrogen Feedback Loop
Carrying excess body fat doesn’t just correlate with low testosterone. It actively drives it down through a specific biological mechanism. Fat tissue contains an enzyme called aromatase, which irreversibly converts testosterone into estrogen. The more fat you carry, the more aromatase activity you have, and the more testosterone gets converted before your body can use it. The result is lower testosterone and higher estrogen levels simultaneously.
This creates a frustrating cycle. Low testosterone makes it harder to maintain muscle and easier to gain fat, which increases aromatase activity, which lowers testosterone further. Weight loss can break the cycle, and studies consistently show that significant fat loss raises testosterone levels even without hormone therapy. This is one of the most common and most reversible causes of low testosterone in younger men.
Medications That Suppress Testosterone
Several widely prescribed medications lower testosterone as a side effect, and opioid painkillers are among the most significant. Opioids act on receptors in the hypothalamus, disrupting the normal signaling that tells the pituitary gland to release luteinizing hormone. Without that signal, the testes produce less testosterone. Opioids can also raise prolactin levels, which further suppresses the hormonal chain. These effects aren’t limited to high doses or long-term use, though both make the problem worse.
Corticosteroids (like prednisone), certain antidepressants, and drugs used to treat prostate conditions can also lower testosterone. Anabolic steroids, ironically, are a common culprit. When you introduce synthetic testosterone or related compounds from outside the body, your brain detects the elevated levels and shuts down its own production signals. After stopping steroids, it can take months or even longer for natural production to recover, and in some cases it never fully does.
Sleep Apnea and Disrupted Sleep
Most of your daily testosterone is produced during sleep, particularly during deep sleep phases. Obstructive sleep apnea fragments sleep architecture and causes repeated drops in blood oxygen throughout the night. Both of these problems independently suppress the hormonal signaling that drives testosterone production.
Research shows that when deep sleep is disrupted, the normal nighttime rise in testosterone is considerably blunted. The low-oxygen episodes characteristic of sleep apnea also appear to directly suppress the brain’s hormonal signals to the testes. Because sleep apnea often accompanies obesity, these two causes frequently compound each other. Treating the sleep disorder with a CPAP machine can help restore more normal testosterone rhythms, though results vary.
Chronic Diseases
Type 2 diabetes and low testosterone are closely linked. Insulin resistance and the inflammation associated with metabolic syndrome both interfere with testosterone production. The relationship runs in both directions: low testosterone increases the risk of developing type 2 diabetes, and diabetes itself further suppresses testosterone.
Liver disease, kidney disease, and HIV/AIDS also commonly cause low testosterone. Chronic liver disease impairs the body’s ability to produce the proteins that carry testosterone through the bloodstream. Kidney disease can affect both the brain’s signaling hormones and the testes directly. Any serious chronic illness that puts the body under sustained stress can reduce testosterone as the body prioritizes other functions over reproduction.
Genetic and Structural Causes
Klinefelter syndrome is the most common genetic cause. Men with this condition carry an extra X chromosome (47,XXY instead of the typical 46,XY). Their testes develop abnormally, and the cells responsible for making testosterone can’t produce enough of it despite being present in higher-than-normal numbers. The severity varies widely. Some men are diagnosed in childhood, while others don’t find out until they’re evaluated for infertility or low energy in adulthood.
Undescended testes, physical injury to the testes, and prior cancer treatments (particularly chemotherapy or radiation directed at the pelvic area) can all damage the tissue that produces testosterone. Tumors or other conditions affecting the pituitary gland disrupt the hormonal chain from the brain side, cutting off the signal the testes need. Hemochromatosis, a condition that causes iron to build up in organs, can damage both the pituitary gland and the testes.
Environmental Chemical Exposure
A growing body of evidence links certain industrial chemicals to lower testosterone. Phthalates, a class of chemicals found in plastics, food packaging, personal care products, and vinyl flooring, have measurable effects. A large national study using data from over 2,000 men found that higher phthalate exposure was associated with lower testosterone across multiple age groups. Among men 60 and older, each doubling of exposure to one common phthalate group (DEHP, widely used in food packaging and medical devices) was associated with roughly 7.7% lower total testosterone. Younger men aged 20 to 39 showed significant associations between a different group of phthalates and lower free testosterone.
These aren’t dramatic, overnight drops. They represent a subtle but consistent drag on hormone levels that compounds over years of exposure. Because phthalates are nearly ubiquitous in modern environments, complete avoidance isn’t realistic, but reducing exposure through choices like avoiding plastic food containers (especially when heated), choosing fragrance-free personal care products, and eating fewer ultra-processed foods can help limit your intake.
Less Obvious Contributing Factors
Excessive alcohol use suppresses testosterone through multiple pathways, damaging testicular tissue directly and impairing liver function. Even moderate drinking, when sustained over years, can contribute to lower levels.
Extreme endurance exercise and severe caloric restriction can both lower testosterone. The body interprets prolonged energy deficits as a signal that conditions aren’t favorable for reproduction and dials back hormone production accordingly. This is more common in competitive athletes and people on very low-calorie diets than in casual exercisers.
Stress raises cortisol, and sustained high cortisol levels directly interfere with the brain’s testosterone signaling. Chronic psychological stress, whether from work, relationships, or financial pressure, can meaningfully contribute to lower levels over time. Unlike genetic causes, these lifestyle factors are among the most modifiable, and addressing them often improves testosterone without medical intervention.