Low testosterone happens when the body produces less than 300 ng/dL of total testosterone, the threshold used by the American Urological Association for diagnosis. The causes range from natural aging to chronic diseases, medications, lifestyle habits, and genetic conditions. Some are reversible, others are not, but understanding what’s driving the decline is the first step toward addressing it.
How Testosterone Production Works
Testosterone production depends on a chain of signals. The hypothalamus in the brain releases a hormone that tells the pituitary gland to produce two signaling hormones, which travel through the bloodstream and tell the testes to make testosterone. A problem anywhere in this chain can lower levels.
When the testes themselves are damaged or dysfunctional, that’s called primary hypogonadism. When the brain’s signaling system is the problem, it’s called secondary (or central) hypogonadism. The distinction matters because it changes what treatments make sense and whether the underlying cause is fixable.
Age-Related Decline
Testosterone levels drop by roughly 1% per year after age 30. This is normal and happens to virtually all men. By the time you’re 50, you may have 20% less testosterone than you did at your peak. Most men never notice this gradual decline because it stays within the normal range. But when combined with other factors on this list, that slow annual drop can push levels below the threshold where symptoms appear: low energy, reduced muscle mass, decreased sex drive, and mood changes.
Obesity and Excess Body Fat
Carrying excess body fat is one of the most common and most reversible causes of low testosterone. Fat tissue contains an enzyme called aromatase that converts testosterone into estrogen. The more fat you carry, the more of your testosterone gets converted, creating a cycle that’s hard to break: low testosterone promotes more fat storage, and more fat further lowers testosterone.
This isn’t a small effect. Men with obesity consistently show significantly lower testosterone levels than men at a healthy weight, and the relationship is dose-dependent, meaning the more excess fat, the lower the levels tend to be. Weight loss, whether through diet, exercise, or bariatric surgery, reliably raises testosterone. In many cases, losing 10 to 15% of body weight is enough to move levels back into the normal range without any other intervention.
Chronic Health Conditions
Type 2 diabetes is strongly linked to low testosterone. Among men with type 2 diabetes, roughly 37% have below-normal free testosterone levels. That number jumps to 66% in men who also have chronic kidney disease. The relationship goes both ways: low testosterone increases insulin resistance, and poorly controlled blood sugar further suppresses testosterone production.
Liver disease, HIV, and obstructive sleep apnea also lower testosterone through various mechanisms. Iron overload disorders like hemochromatosis can damage both the testes and the pituitary gland, affecting production from both ends of the signaling chain. If you’ve been diagnosed with low testosterone and no obvious cause has been identified, screening for these conditions is a standard part of the workup.
Medications That Lower Testosterone
Several widely prescribed medications suppress testosterone, sometimes dramatically.
Chronic opioid use is one of the most well-documented culprits. Opioids suppress the brain’s signaling to the testes, reducing how much testosterone gets made. They also appear to increase the rate at which existing testosterone is broken down in the liver, brain, and testes. The result is a double hit: less production and faster metabolism of what’s already there. This effect can occur with both prescription painkillers and illicit opioids, and it often develops within weeks of regular use.
Corticosteroids (like prednisone), commonly prescribed for inflammation and autoimmune conditions, suppress the same brain signaling pathway. Anabolic steroids are another major cause. While taking them floods the body with synthetic testosterone, stopping them leaves the brain’s signaling system shut down, sometimes for months. Certain antifungal medications and some chemotherapy drugs can damage the testes directly.
Sleep Deprivation
Most testosterone is produced during sleep, particularly during deep sleep cycles. A study from the University of Chicago found that healthy young men who slept only five hours per night for one week saw their testosterone drop by 10 to 15%. The researchers noted this was equivalent to aging 10 to 15 years in terms of testosterone levels. Five hours isn’t an extreme scenario for many people, which makes sleep one of the most underappreciated factors in hormonal health.
Consistently getting fewer than six hours of sleep doesn’t just cause a temporary dip. Over time, chronic sleep restriction can keep levels persistently low. If you’re experiencing symptoms of low testosterone and you’re sleeping poorly, improving sleep is one of the highest-impact changes you can make.
Genetic Conditions
Some men are born with conditions that affect testosterone production from birth or puberty onward. Klinefelter syndrome, where a man has an extra X chromosome (XXY instead of XY), is the most common genetic cause of primary hypogonadism. It affects roughly 1 in 600 males and often goes undiagnosed until adulthood, when fertility problems or low testosterone symptoms prompt testing.
Kallmann syndrome affects the brain’s ability to produce the signaling hormone that triggers testosterone production. It’s distinguished from other hormonal conditions by one unusual feature: men with Kallmann syndrome typically have a reduced or completely absent sense of smell. This happens because the nerve cells responsible for hormonal signaling and the nerve cells for smell both fail to migrate to the correct location during fetal development.
Nutritional Deficiencies
Vitamin D and zinc both play direct roles in testosterone production. Research on healthy men with normal testosterone found that blood levels of vitamin D and testosterone were closely linked. When activated vitamin D was applied directly to testicular tissue in lab studies, the tissue produced more testosterone than untreated tissue, suggesting vitamin D affects production right at the source. Men with low vitamin D also showed reduced responsiveness to the brain’s signaling hormones, meaning even when the brain sent the right signals, the testes didn’t respond as strongly.
Zinc deficiency produces similar effects. Zinc is essential for the enzymes involved in making testosterone, and even mild deficiency can lower levels. Both nutrients are easy to test for and straightforward to correct through diet or supplementation.
Environmental Chemical Exposure
Endocrine-disrupting chemicals are synthetic compounds that interfere with hormone production or function. Phthalates, found in plastics, personal care products, and food packaging, are among the most studied. Exposure during fetal development is particularly concerning: during a critical window of testicular development, these chemicals can interfere with masculinization in ways that affect reproductive health years or decades later.
Perfluorinated compounds (the “forever chemicals” found in nonstick coatings, water-resistant fabrics, and many consumer products) are widespread in the environment and in human blood. Industrial chemicals called organotins, historically used in marine paints, also have documented effects on male reproductive hormones. Reducing exposure is difficult since these chemicals are so pervasive, but avoiding plastic food containers for hot foods, filtering drinking water, and choosing fragrance-free personal care products can lower your exposure over time.
Physical Trauma and Medical Treatments
Direct injury to the testes, whether from sports, accidents, or surgery, can permanently reduce their ability to produce testosterone. Radiation therapy targeting the pelvic area or the brain (near the pituitary gland) can damage testosterone production from either end of the signaling chain. Chemotherapy drugs are toxic to the cells that produce testosterone, and while levels sometimes recover after treatment ends, the damage can be permanent.
Head injuries and pituitary tumors can disrupt the brain’s hormonal control center. Even a concussion, if severe enough, can temporarily or permanently reduce the pituitary’s output. Infections also pose risks: mumps that spreads to the testes is a classic cause of primary testicular failure, though vaccination has made this far less common.
Rapid Weight Loss and Caloric Restriction
While obesity lowers testosterone, losing weight too quickly can temporarily do the same thing. Severe caloric restriction, eating disorders like anorexia nervosa, and rapid weight loss after bariatric surgery all suppress the brain’s hormonal signaling. The body essentially interprets starvation as a signal to shut down reproductive function. This form of low testosterone is usually reversible once nutrition stabilizes and weight loss slows to a sustainable pace.