Age related decreases in the male sex hormone testosterone are common in older men; some 30% of men over age 55 have it. Low levels of the hormone can cause symptoms of fatigue, a decreased sex drive, and irritability. However, because some symptoms of this disorder are similar to symptoms of depression, the link between the two disorders has been unclear.
In this study, researchers analyzed medical records over a two-year period for 278 men -- all age 45 and over -- who had no diagnosis of depression before that time period. These were also men who had low or normal levels of testosterone test results. Doctors often order these tests when there are libido or other sexual function problems.
During the two-year period, the men with low testosterone were four times more likely to be diagnosed with clinical depression, reports researcher Molly M. Shores, MD, with the Veterans Affairs Puget Sound Health Care System and the University of Washington in Seattle.
Her study appears in the Archives of General Psychiatry.
Older Men at Risk
This might happen because low testosterone levels trigger symptoms such as anorexia, fatigue, and decreased libido, which may have an effect on mood.
Or, as one study of mice showed, low testosterone may directly alter brain chemistry -- specifically serotonin levels. Studies of humans show that serotonin levels are lower in older adults with clinical depression.
"Older men would be particularly vulnerable to these effects, because serotonin receptors are already decreased from normal aging," writes Shores.
Primary care doctors often don't recognize depression in these patients. And testosterone levels are rarely checked when signs of clinical depression are evident, she explains.
"Because depression is a major risk factor for suicide, and older men have the highest suicide rate of any age group in the United States, identifying conditions [such as low testosterone] that increase the risk of depressive illness could be an important opportunity for early intervention and treatment," she writes.
Treatment for both clinical depression and low testosterone could improve quality of life for older men, she writes. However, questions remain about the risks of prostate cancer related to testosterone replacement therapy -- which future studies need to address, says Shores.