A new study finds that a drop in testosterone levels over time is more likely to result from a man's behavioural and health changes, than by ageing.
"Declining testosterone levels are not an inevitable part of the ageing process, as many people think," said study co-author Gary Wittert, MD, professor of medicine at the University of Adelaide in Adelaide, Australia. "Testosterone changes are largely explained by smoking behaviour and changes in health status, particularly obesity and depression."
Many older men have low levels of the sex hormone testosterone, but the cause is not known. Few population-based studies have tracked changes in testosterone levels among the same men over time, as their study did, Wittert said.
How the study was done
In this study, supported by the National Health and Medical Research Council of Australia, the authors analysed testosterone measurements in more than 1 500 men who had measurements taken at two clinic visits five years apart. All blood testosterone samples underwent testing at the same time for each time point, according to Wittert.
After the researchers excluded from the analysis any men who had abnormal lab values or who were taking medications or had medical conditions known to affect hormones, they included 1 382 men in the data analysis. Men ranged in age from 35 to 80 years, with an average age of 54.
On average, testosterone levels did not decline significantly over five years; rather, they decreased less than 1% each year, the authors reported. However, when the investigators analysed 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.
"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."
What the study showed
Past research has linked depression and low testosterone. This 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 ageing and that they are most likely due to health-related behaviours or health status itself," he said.
Unmarried men in the study had greater testosterone reductions than did married men. Wittert attributed this finding to past research showing that married men tend to be healthier and happier than unmarried men. "Also, regular sexual activity tends to increase testosterone," he explained.
(EurekAlert, June 2012)
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