Testosterone drops for a wide range of reasons, from the predictable effects of aging to underlying health conditions, medications, and lifestyle factors. The average decline is about 1% per year after age 30, but that gradual slide doesn’t fully explain why some men end up well below the clinical threshold of 300 ng/dL, which is the level the American Urological Association uses to support a diagnosis of low testosterone. Understanding the specific cause matters because many of these factors are treatable or reversible.
How the Hormone System Works
Testosterone production depends on a chain of signals between your brain and your testes. The hypothalamus (a small region at the base of the brain) releases a signaling hormone that tells the pituitary gland to produce two other hormones: LH and FSH. LH then travels through the bloodstream to specialized cells in the testes called Leydig cells, which actually manufacture testosterone. A problem at any point in this chain can result in low levels.
When the testes themselves are damaged or dysfunctional, the brain keeps sending louder and louder signals (higher LH levels) trying to get a response. This is called primary hypogonadism, or testicular failure. It tends to cause more noticeable physical changes like reduced testicular size and breast tissue growth. When the problem is in the brain’s signaling instead, LH stays normal or drops, and the testes never get the message to produce testosterone in the first place. This second pattern, called secondary hypogonadism, is actually more common and is the type linked to obesity, opioid use, and type 2 diabetes.
Normal Aging vs. Abnormal Decline
A slow, steady drop in testosterone is a normal part of getting older. Starting around age 30, levels fall roughly 1% per year. For most men, this gradual decline never causes symptoms. But when the drop is steeper than expected, or when it’s compounded by other factors like weight gain or chronic illness, levels can fall into the range where fatigue, low sex drive, difficulty concentrating, and loss of muscle mass become noticeable.
Age alone rarely pushes a healthy man into severely low territory. When a younger man or a man with dramatic symptoms gets tested and comes back well below 300 ng/dL, something beyond normal aging is usually going on.
Excess Body Fat
Carrying extra weight is one of the most common and underappreciated reasons testosterone drops. Fat tissue contains an enzyme called aromatase that converts testosterone directly into estrogen. The more fat you carry, the more of this conversion happens, and the less testosterone remains in circulation. This creates a frustrating feedback loop: low testosterone makes it easier to gain fat, and more fat drives testosterone even lower.
The relationship between obesity and low testosterone is strong enough that weight loss alone can meaningfully raise levels in men who are overweight. Even moderate reductions in body fat can slow the aromatase-driven conversion and allow more testosterone to stay in the bloodstream.
Type 2 Diabetes and Metabolic Disease
Between 25% and 40% of men with type 2 diabetes have low testosterone. In most of these cases, the problem originates in the brain’s signaling system rather than in the testes. Insulin resistance and chronic inflammation appear to suppress the hypothalamus and pituitary, reducing the hormonal signals that trigger testosterone production. This makes type 2 diabetes one of the single biggest risk factors for clinically low testosterone in men under 60.
Other metabolic conditions, including metabolic syndrome and chronic kidney disease, follow a similar pattern. The common thread is that systemic inflammation and disrupted metabolism interfere with the brain-to-testes communication pathway.
Medications That Lower Testosterone
Several widely prescribed drug classes can suppress testosterone, sometimes significantly. Opioid painkillers are the most well-documented culprit. They act on the hypothalamus and pituitary gland simultaneously, reducing the signaling hormones that tell the testes to produce testosterone. They also raise levels of prolactin, a hormone that further suppresses those signals. The effect is dose-dependent and begins quickly after starting the medication.
Glucocorticoids (prescribed for conditions like asthma, arthritis, and autoimmune diseases) also suppress the signaling chain. Long-term use of these anti-inflammatory drugs can produce measurable drops in testosterone. If you’re on any of these medications and experiencing symptoms like fatigue, low libido, or mood changes, the medication itself may be a contributing factor worth discussing with whoever prescribed it.
Sleep Deprivation
Testosterone production peaks during sleep, particularly during deep sleep stages. Cutting that short has real consequences. In a controlled study of healthy young men, restricting sleep to just 5 hours per night for 8 consecutive nights reduced testosterone levels by up to 15%. That’s a substantial drop, roughly equivalent to aging 10 to 15 years, and it happened in men who were otherwise healthy and in their twenties.
Chronic sleep restriction doesn’t have to be extreme to matter. Consistently getting 5 or 6 hours instead of 7 or 8 chips away at testosterone over time, and the effects compound when paired with other risk factors like stress or weight gain. Sleep apnea, which repeatedly interrupts deep sleep throughout the night, is another common and often undiagnosed contributor.
Nutritional Deficiencies
The testes need specific raw materials to manufacture testosterone, and running low on certain nutrients can directly impair production. Zinc is essential for Leydig cell function. Magnesium supports the activity of key enzymes involved in testosterone synthesis, and animal studies have shown that magnesium supplementation can increase the activity of these enzymes and raise circulating testosterone levels. Vitamin D also plays a role, and deficiency is extremely common in people who spend most of their time indoors or live in northern climates.
These deficiencies are particularly relevant because they’re easy to test for and straightforward to correct. A diet consistently low in nuts, seeds, leafy greens, meat, and shellfish can leave you short on zinc and magnesium. Vitamin D levels are simple to check with a blood test.
Environmental Chemicals
A growing body of evidence points to synthetic chemicals in everyday products as a factor in declining testosterone levels across populations. Phthalates, found in plastics, food packaging, and personal care products, can directly inhibit testosterone production in Leydig cells. One well-studied phthalate, DEHP, disrupts both Leydig and Sertoli cell function and interferes with the enzymes responsible for testosterone synthesis.
BPA, another common plasticizer, has been inversely correlated with free androgen levels in studies of otherwise fertile men. These chemicals are classified as endocrine disruptors because they mimic estrogen or block androgen activity in the body. While the effect of any single exposure may be small, the cumulative load from food containers, water bottles, receipts, and household products adds up over a lifetime. Reducing exposure by avoiding plastic food storage (especially when heated), choosing fragrance-free products, and filtering drinking water can help limit intake.
Other Medical Causes
Several other conditions can cause low testosterone. Injuries to the testes, including from surgery, trauma, or torsion, can directly damage the tissue that produces the hormone. Infections like mumps orchitis (a complication of mumps that inflames the testes) can have lasting effects on production. Genetic conditions like Klinefelter syndrome, where a man carries an extra X chromosome, cause primary testicular failure from birth.
Pituitary tumors, even benign ones, can disrupt the hormonal signaling chain by producing excess prolactin or by physically compressing the gland. Hemochromatosis, a condition where the body stores too much iron, can damage both the pituitary and the testes. Head injuries that affect the pituitary, radiation therapy to the head or pelvis, and certain autoimmune conditions round out the list of less common but important causes. Many of these are identifiable with blood work and imaging, which is why a thorough workup matters when testosterone comes back low.