March 4, 2008

Testosterone Levels Linked to Depression

A new Australian study found men over 70 with low testosterone levels may be more susceptible to depression.  

In the study, a team of researchers from University of Western Australia examined about 4,000 men aged 70 or older and found a three-fold increase in depression among those with the lowest testosterone levels. 

The scientists believe the hormone may affect levels of key brain chemicals associated with depression.

Previous research had found among those under 65, women were more likely to be depressed than men.  However, after age 65 the difference in depression rates between the genders becomes negligible.

In performing their study, the Australian research team examined 3,987 men over the age of 70.  Each participant gave blood samples and took tests to determine if they were depressed.  In total, 203 of the participants were assessed as being depressed, and had substantially lower levels of both total testosterone and free testosterone, which is not bound to proteins.

The researchers adjusted the data to account for additional factors such as educational attainment and body fat levels.  They found those participants whose level of free testosterone was in the bottom 20% were three times more likely to be depressed than those in the top 20%.

The researchers said further work was required to confirm their findings. Testosterone levels decline with age, but with wide variation.  But the study raises the possibility that effective treatments for depression might come from boosting testosterone levels in older men.

Previous studies on testosterone and depression had revealed links between the two.   A study of 800 men over 50 found those with low testosterone levels had a 33% increased risk of death over an 18-year period than those with higher levels.  

Those with low testosterone levels appeared significantly more likely to have a cluster of risk factors associated with cardiovascular disease and diabetes, raising the possibility that men with low testosterone may be prone to depression because they are also more likely to be in poor physical health.

However, the Australian research found that this could not fully explain the association, and suggests other factors must also be at work.

Professor David Kendall, a pharmacology expert at the University of Nottingham in the UK, told BBC News there was a wealth of evidence that testosterone levels are linked to mood.  For instance, farmers had long castrated their stock to pacify them.  Animal research has also shown that removal of the gonads blocked the action of anti-depressants on key mood-controlling chemicals in the brain.

"It would be no surprise that low testosterone reduces mood," Kendall said.

"Testosterone therapy offers a relatively simple intervention, potentially, for some groups of older depressives with hypogonadism (low production of sex hormones)."

Professor Stafford Lightman, a hormone expert at the University of Bristol, said testosterone potentially had many small effects that could raise depression risks. For instance, low levels have been linked to poor cognitive performance, and indeed testosterone replacement therapy has been shown to help some elderly men with mild Alzheimer's disease.

However, Kendall said that depression, particularly in the elderly, was often the result of many different, inter-relating factors, and warned against placing too much emphasis on any one factor alone.

"My view is that low testosterone could be a contributory factor to depression, but probably not a very powerful one," he said.

Research suggests that levels of testosterone in men of all ages are falling.


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University of Western Australia

The study was published in the journal Archives of General Psychiatry. An abstract of the report can be viewed at http://archpsyc.ama-assn.org/cgi/content/short/65/3/283.