While depression is common among HIVers, new research by scientists in Australia has shown why some older men may be especially prone to the condition: declining testosterone levels. A study of 4,000 men reported in the Archives of General Psychiatry found that men with the lowest testosterone levels were three times more likely to be depressed than those with the highest levels.

The researchers suspect low levels of the hormone may affect key brain chemicals, raising the risk for depression. Because testosterone levels normally decline with age, the researchers suggest, HIV-positive men experiencing depression should consider speaking with their physicians about testosterone-replacement therapy.