About one in four active-duty US military personnel may have testosterone levels below a commonly used clinical threshold, according to a study published in JAMA, potentially placing around 100,000 service members below the benchmark targeted by a screening policy introduced by Defence Secretary Pete Hegseth.
The study found that 25.7% of a representative sample of 500 active-duty soldiers had testosterone concentrations below 300 nanograms per decilitre, a threshold commonly used to identify possible testosterone deficiency. About 15% had levels below the stricter threshold of 264 nanograms per decilitre. The researchers extrapolated their findings to estimate the number of military personnel who might fall below the higher threshold.
Hegseth announced last summer that all members of the armed forces over 30 would have their testosterone levels tested as part of routine medical examinations. He said the policy was intended to prepare service members for a modern battlefield that was “brutal and unforgiving”. The tests were incorporated into medical check-ups from August, but their results have not been made public.
The study has important limitations. Testosterone was measured only once in each participant, rather than repeatedly as medical guidance recommends when assessing possible hypogonadism, a condition in which the body produces insufficient testosterone. Claire Berryman, the study’s lead author, said the findings were not entirely surprising and were broadly comparable with levels observed in the general US population, suggesting that low concentrations might be similarly prevalent among civilians and military personnel. The sample had an average age of 29.9 years.
Testosterone levels have gradually declined worldwide over recent decades, with scientific evidence linking the trend to rising obesity and sedentary lifestyles, according to Manuel Tena-Sempere, a physiologist at the University of Córdoba. Hypogonadism can cause symptoms including depression, erectile dysfunction and fatigue. An estimated 5.6% of men aged between 30 and 79 have the condition.
The growing cultural prominence of testosterone, however, extends beyond its medical role. The hormone has become a focus of discussions about masculinity among parts of the American political right and the online “manosphere”, a community associated with extreme views on masculinity and anti-feminism.
Testosterone replacement therapy (TRT) has expanded sharply in the United States, rising from fewer than one million prescriptions in 2000 to nearly 12 million in 2025. Although the treatment has legitimate medical uses, it has increasingly been promoted as a means of building muscle and increasing sexual desire. An article published by the Endocrine Society found that only 12% of men receiving the therapy met the diagnostic criteria for treatment.
María Papaleontiou, an endocrinologist who authored that article, warned that long-term testosterone replacement was not without risks and could require continuing medical supervision. She said a single low reading could not establish hypogonadism because testosterone levels fluctuate according to the time of day, illness, sleep, diet, medication and laboratory testing conditions. The latest study, she said, indicated a trend rather than establishing the presence of disease.
Hegseth has nevertheless promised to offer testosterone replacement therapy to soldiers whose test results fall below the specified threshold, without explicitly limiting treatment to those diagnosed with hypogonadism. Berryman said her research had not directly assessed whether testosterone concentrations were associated with military performance. A reading below a particular threshold does not necessarily indicate reduced physical capability or an inability to perform military duties.
Tena-Sempere said the study’s findings also pointed towards body weight as a possible factor. The participants had an average body mass index of 28.5, within the overweight range. The study found that each five-point increase in BMI was associated with approximately 90% higher odds of having a testosterone concentration below 300 nanograms per decilitre.
The findings come as Hegseth has placed increasing emphasis on testosterone as part of his vision for the US armed forces. Last year, he also prohibited transgender people from serving in the military, arguing that they would not be able to access hormone treatment in combat zones.
Describing the type of personnel he wanted in the armed forces, Hegseth said: “No fat people, no transgenders, no beards, no weirdos, no cowards, no radicals. Only warriors.”
