For many men, testosterone levels drop as they get older, but new research presented at a conference this week suggests this is not necessarily a consequence of age itself, but more to do with behavior, such as smoking, and changes in health, such as obesity and depression.

In men, the hormone testosterone is made in the testicles and controls the development of their sexual characteristics. It influences wellbeing, sexual function and fertility and also helps maintain a healthy body composition, develop muscle bulk, sufficient levels of red blood cells, and protect bone density.

Study co-author Dr Gary Wittert, professor of medicine at the University of Adelaide, told the press:

“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 added.

Past research has shown that many men have low levels of testosterone, and some have linked depression and low testosterone, but few population studies have followed the same group of men over time, said Wittert.

For the latest study, the researchers analyzed testosterone measurements in more than 1,500 men who had their hormone levels tested twice, with a five year gap between clinic visits. All the samples were tested at the same point in time before, and then after, the five-year gap, said Wittert.

Wittert and colleagues only included 1,382 men in their analysis because they took out the ones who were on medication or had health conditions that affect hormone levels. The men they included had an average age of 54 (range was 35 to 80 years).

They found that the average testosterone level fell by an insignificant 1% a year between the first sampling and the second, five years later.

However, within subgroups, they found a noticeably different pattern: certain factors appeared to influence more significant drops in hormone levels over the period.

The biggest falls in testosterone were among men who became obese, had stopped smoking, or were depressed at either of the clinic visits, said Wittert, adding that:

“While stopping smoking may be a cause of a slight decrease in testosterone, the benefit of quitting smoking is huge.”

The study also showed that of the participants, unmarried men experienced larger drops in testosterone than married men.

Wittert said this finding probably supports that of other studies that suggest married men tend to be happier and in better health than single men. He also said that regular sexual activity tends to raise levels of testosterone.

The study was funded by the National Health and Medical Research Council of Australia.

Dr Andre Araujo, a visiting professor at the University of Adelaide in Australia, and vice president of epidemiology at New England Research Institutes, in Watertown, Massachusetts in the US, is presenting the findings at the Endocrine Society’s 94th Annual Meeting in Houston, Texas, USA, this week.

Written by Catharine Paddock