Older men with low blood levels of free testosterone appear to have a higher prevalence of depression than peers with higher blood levels, according to an article in the March issue of Archives of general Psychiatry.

According to background information in the article, women are more likely to be depressed than men until age 65 years, when sex differences almost disappear. Several studies have suggested that sex hormones might be responsible for this phenomenon.

Osvaldo P. Almeida, MD, PhD, of the University of Western Australia, Perth, and colleagues studied 3,987 men 71 to 89 years old. Between 2001 and 2004, the men completed a questionnaire reporting information about demographics and health history. They underwent testing for depression and cognitive difficulties, and information about physical health conditions was obtained from a short survey and an Australian health database. The researchers collected blood samples from the participants and recorded levels of total testosterone and free testosterone.

A total of 203 participants (5.1 percent) met criteria for depression; these men had significantly lower total and free testosterone levels then men who were not depressed. After controlling for other factors-such as education level, body mass index and cognitive scores-men in the lowest quintile (20 percent) of free testosterone concentration had three times the likelihood of depression compared with men in the highest quintile.

The mechanism by which low hormone levels might affect depression risk has not been identified, but might involve changes in the levels of neurotransmitters or hormones in the brain, the authors noted.

"A randomized controlled trial is required to determine whether reducing prolonged exposure to low free testosterone is associated with a reduction in the prevalence of depression in elderly men," the authors wrote. "If so, older men with depression may benefit from systematic screening of free testosterone concentration, and testosterone supplementation may contribute to the successful treatment of hypogonadal older men with depression."