Older men with lower levels of the male sex hormone testosterone in their blood may be more prone to depression, a study suggests. A study of about 4,000 men aged over 70 found those with lowest testosterone were three times more likely to be depressed than those with the most.

Researchers suspect the hormone may affect levels of key brain chemicals. The study, by the University of Western Australia, features in Archives of General Psychiatry. Research has found that women are more likely to be depressed than men until the age of 65, when the difference between the genders almost disappears.