New research is challenging the long-held belief that declining testosterone levels in men are a normal part of aging.
Australian researchers have found a drop in levels of the male hormone over time is more likely to result from a man's lifestyle, behavior, weight, outlook and overall health than by growing older.
"Declining testosterone levels are not an inevitable part of the aging process, as many people think," said Dr. Gary Wittert, of the University of Adelaide in Adelaide, who conducted the study presented at The Endocrine Society's 94th Annual Meeting in Houston. "Testosterone changes are largely explained by smoking behavior and changes in health status, particularly obesity and depression."
Wittert noted many older men have low levels of testosterone, but few studies have tracked changes in the sex hormone among the same men over time – as the new research did.
For the study, supported by the National Health and Medical Research Council of Australia, Wittert and colleagues analyzed testosterone measurements taken from more than 1,500 men at two clinic visits five years apart. The men ranged in age from 35 to 80 years, with an average age of 54.
On average, researchers found testosterone levels did not decline significantly over five years. But they found certain factors were linked to lower testosterone levels at five years in some of the study participants.
"Men who had declines in testosterone were more likely to be those who became obese, had stopped smoking or were depressed at either clinic visit," Wittert said. "While stopping smoking may be a cause of a slight decrease in testosterone, the benefit of quitting smoking is huge."
Unmarried men also had greater testosterone reductions than did married men. Wittert attributed this finding to past research showing married men tend to be healthier and happier than unmarried men.
"Also, regular sexual activity tends to increase testosterone," he explained.
Wittert noted the hormone is important for many bodily functions, including maintaining a healthy body composition, fertility and sex drive.
"It is critical that doctors understand that declining testosterone levels are not a natural part of aging and that they are most likely due to health-related behaviors or health status itself," he said.