HOUSTON—Declines in testosterone levels may not be inevitable with aging, but instead could be due to changes in smoking habits, body size, mental health status and chronic cardiovascular disease, according to new findings presented at The Endocrine Society’s 94th Annual Meeting.

Many older men have low levels of testosterone, but the cause is not known, said study investigator Gary Wittert, MD, Professor of Medicine at the University of Adelaide in Adelaide, Australia.  Few population-based studies have tracked changes in testosterone levels among the same men over time. Dr. Wittert and his colleagues analyzed testosterone levels in the longitudinal Male Adelaide Inflammation Lifestyle Environment Study, which enrolled 1,869 community-based men.

“Men who had declines in testosterone were more likely to be those who became obese, had stopped smoking, were depressed at either clinic visit, or who had persistent or new onset cardiovascular disease,” Dr. Wittert said.

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After the researchers excluded from the analysis any men who had established disorders of the testes, or who were taking medications or had medical conditions known to affect hormones, they included 1,382 men in the data analysis. The men ranged in age from 35 to 80 years, with a mean age of 54 at baseline. The researchers accumulated complete data at baseline and at five years.

On average testosterone levels did not decline significantly over the study period, with an average decrease of less than 1% each year. At baseline, 21% of the men were unmarried and 19% were current smokers. In addition, 30% of the men had a body mass index (BMI) of 30 kg/m2 or higher (obese), 48% had a waist circumference of 100 cm or more (central obesity), and 8% were depressed at baseline. The mean baseline testosterone level was 16.2 nmol/L (3% below 8 nmol/L, 36% 8-15 nmol/L, and 61% greater than 15 nmol/L). At follow-up, the mean testosterone level was 15.6 nmol/L. The study showed that this represented a non-significant 0.13 nmol/L decline per year or 0.80% per year.

When the investigators analyzed the data by subgroups, they found that certain factors were linked to lower testosterone levels at five years than at the beginning of the study. Compared with married men, unmarried men had a significantly greater yearly decline in testosterone levels. Men who quit smoking during the study had a significantly greater annual decline than nonsmokers. The researchers also observed significantly greater annual declines among men who developed central obesity (versus those who did not have central obesity) and among those who became obese during the study (versus those with a BMI below 25), had persistent depression at both time points, or persistent or new onset cardiovascular disease.

Although a transition from normal weight to obesity resulted in decreases in testosterone, the researchers found no increases in luteinizing hormone. They theorize that a failure at the hypothalamic/pituitary level may help explain the lower testosterone levels. They believe their findings are clinically relevant because they suggest that preventing obesity could be an important strategy for preventing testosterone declines.

“Testosterone deficiency can be a marker of underlying disease,” Dr. Wittert said. “Urologists should care about these findings for two reasons. To dismiss declining testosterone levels as a consequence of aging instead of correcting the underlying problem is one reason. The second reason is that people see [supplemental] testosterone as a panacea and we don’t have any long-term data to support that.”