Journal of the Endocrine Society: Testosterone Levels Linked to Abdominal Fat

The main factor associated with lower testosterone levels in men was not age but the amount of visceral fat — the fat that accumulates in the abdominal cavity around the internal organs. The more visceral fat a man has, the lower his level of the male sex hormone tends to be. This association was substantially stronger than the relationship between testosterone and age. Researchers from the U.S. Army Research Institute of Environmental Medicine reached this conclusion after analyzing data from nearly 5,000 American men aged 20 to 59. The study was published in the Journal of the Endocrine Society.

It is commonly believed that testosterone inevitably declines with age. While the decline does indeed begin at around age 35, it occurs very gradually. When the researchers took body-fat distribution into account, they found that within the age range studied, age itself was only weakly associated with hormone levels. By contrast, the researchers identified deep abdominal fat as the main fat-related measure associated with low testosterone.

Visceral fat is metabolically active, contributes to chronic inflammation, and increases the conversion of testosterone into estrogens. This may create a vicious cycle: excess fat lowers testosterone, while low testosterone may contribute to further weight gain. According to estimates from earlier studies, an increase of four to five units in body mass index (BMI) has an effect on testosterone roughly comparable to that of 10 years of aging.

The authors emphasize that the relevant risk indicator is specifically waist circumference and the amount of abdominal fat, rather than overall body weight. A man with a normal body weight but a pronounced belly may have lower testosterone than a heavier man without abdominal obesity.

The researchers add that regular physical activity, reducing calorie intake, and cutting back on simple carbohydrates can help reduce visceral fat, while returning to a healthy weight may partially restore testosterone levels.