Adiposity may account for much of the testosterone decline commonly attributed to aging. Digest
Low testosterone is often viewed as a consequence of getting older. A study examined how body fat compared with age in accounting for differences in testosterone levels among adult men.
The analysis drew on nationally representative US health survey data collected from 2011 to 2016. It included 4,984 men aged 20 to 59, each with a single blood measurement of total testosterone. Researchers compared statistical models relating testosterone to age alone with models that also included body fat or waist circumference.
- Within every age decade studied, men with testosterone below the commonly used 300 ng/dL cutoff for low testosterone had a higher total body-fat percentage than those with levels at or above it.
- Including an adiposity marker alongside age explained about 18–20% of the variation in testosterone levels, compared with just 2.5% for age alone.
- After accounting for age, predicted testosterone fell from about 500 to 300 ng/dL as waist circumference increased from 80 to 120 cm, from about 900 to 250 ng/dL as body fat rose from 5% to 45%, and from about 700 to 230 ng/dL as visceral fat area increased from below 50 to above 300 cm².
- A simple waist measurement explained differences in total testosterone about as well as measuring visceral fat with a body scan.
Fat tissue contains aromatase, an enzyme that converts testosterone into estradiol, a form of estrogen. Greater conversion can lower testosterone while strengthening estradiol's signal to the brain and pituitary to reduce testosterone production. Inflammation and insulin resistance associated with excess body fat can further interfere with testosterone regulation. Low testosterone can in turn promote fat gain, making the relationship potentially two-way, but the study could not determine how much each pathway contributed.
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Body composition can provide useful context when interpreting a low testosterone result in men. However, confirming a clinical disorder requires repeat measurements together with an assessment of symptoms.