Testosterone levels are decreasing among adolescent and young adult (AYA) men in the United States, but obese men with higher-than-recommended levels of physical activity have a reduced likelihood of low testosterone, according to the findings of separate studies presented May 15 during an American Urological Association 2020 Virtual Experience press conference.

In an analysis of data from 4045 AYA men aged 15 to 39 years who participated in the National Health and Nutrition Examination Surveys (NHANES) and had their total testosterone (TT) levels measured during 1999-2016, TT was significantly lower among those in the later (2011-2016) compared with earlier (1999-2000) survey cycles, Soum D. Lokeshwar, MD, an incoming urology resident at Yale School of Medicine, reported. Mean TT decreased over time from 605.39 ng/dL in 1999-2000 to 567.44, 424.96, 431.76, and 451.22 ng/dL in 2003-2004, 2011-2012, 2013-2014, and 2015-2016, respectively, The declining trend was statistically significant.

Elevated body mass index (BMI) was significantly and independently associated with decreased TT levels, with mean BMI rising from 25.83 kg/m2 in 1999-2000 to 27.21, 27.12, 27.81, 27.96 kg/m2 in 1999-2000, 2003-2004, 2011-2012, 2013-2014 and 2015-2016, respectively. Even in men with normal BMI (18.5-24.9 kg/m2), TT levels declined from 664.79 to 529.24 ng/dL between 1999-2000 and 2015-2016.

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The decline in testosterone in AYA men in the United States has many potential causes. “The biggest and most seemingly obvious may be the rise in obesity and BMI in young men,” Dr Lokeshwar told listeners. According to the Centers for Disease Control and Prevention, the US prevalence of obesity was 13.9% in 1999-2000, and this rose to 18.5% in 2015-2016, he pointed out.

Other possible explanations include a decline in physical activity and changes in body composition over time. “Even in men with a normal BMI, body fat percentage may have increased on a national scale, which may be due to this decrease in physical activity,” he said.

Declining testosterone levels in AYA men with increased obesity could lead to the early development of cancer. In addition, low testosterone has been associated with diminished libido and may increase the likelihood of erectile dysfunction.

“And testosterone levels in AYA men are utilized as the benchmark normal levels for testosterone,” Dr Lokeshwar said. “This is very scary because generally when we think of normal values of testosterone, we treat based upon this age group. This may ultimately lead to the undertreatment of testosterone deficiency, which can have large ramifications and severe consequences.”

For the study looking specifically at the effect of physical activity and serum testosterone levels, Richard Fantus, MD, of the University of Chicago, and collaborators used 2011-2016 NHANES data from 7597 men who met inclusion criteria. The investigators converted all physical activity into metabolic equivalent of task (MET) minutes per week. Using recommendations from the US Physical Activity Guidelines Advisory Committee, Dr Fantus’ team divided the cohort into 3 groups based on activity level: less than recommended (below 500 MET minutes per week), recommended (from 500 to 1000 MET minutes per week), and greater than recommended (above 1000 MET minutes per week).

Of the 7597 men, 4461 (58.7%) exceeded the recommended activity level, 703 (9.3%) met the recommended activity level, and (32%) did not meet the recommended activity level. Low testosterone (less than 300 ng/dL) was detected in 2201 men (29%). On multivariable analysis, men whose activity level exceeded the recommended activity level had significant 37% decreased odds of low testosterone compared with those who had lower than recommended activity levels (reference group). Meeting the recommended physical activity levels had no significant effect on the likelihood of low testosterone.

When the investigators stratified the population according to BMI, they found that the association of higher-than-recommended activity with a reduced risk of low T was present only among obese men.

When counseling men regarding low T and exercise, “it’s incredibly important to really counsel the obese population, as exercise independent of weight loss may show additional benefits,” Dr Fantus said.

Dr Fantus gave examples of how various levels of physical activity are defined using METS. Light activity is 1.6-2.9 METS, and would include activity that does not change heart rate, such as walking slowly and cooking. Moderate activity is 3.0-5.9 METS (activity that does not interrupt conversation, walking more than 3 MPH, mowing the lawn). Vigorous activity is 6 METS or more, and this would be activity that prohibits continuous conversation, such as jogging and bicycling uphill.

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Patel P, Fantus R, Lokeshwar S, et al. Trends in serum testosterone levels among adolescents and young adult men in the United States. Presented at the American Urological Association 2020 Virtual Experience held in May. Abstract MP78-01.

Fantus R, Chang C, Bennet N, et al. The association between exercise and serum testosterone among men in the United States. Presented at the American Urological Association 2020 Virtual Experience held in May. Abstract PD25-03.