Taking an aspirin pill a day could help combat depression in the elderly.
Trials found a regular dose reduced the risk in sufferers by around 40 per cent.
It seems to work by lowering levels of homocysteine, an acid in the blood thought to increase the chances of heart attacks and strokes when levels are too high.
Now some scientists think excess homocysteine may also be a factor in poor mental health and that nearly one in six cases of depression in the elderly could be avoided by using aspirin to lower levels in the blood.
Up to 20 per cent of us suffer depression at some point in our lives, with women affected more than men.
And the elderly are at high risk because of the effect from declining health, bereavements and loneliness.
To test whether lowering homocysteine levels prevented depression, scientists at the University of Western Australia in Perth studied 3,700 men aged between 69 and 87 and monitored their medical records to see which ones had a history of depression.
They were also tested to see if they had raised levels of homocysteine. The findings, published in the journal Translational Psychiatry, showed men with excessive homocysteine levels were 60 per cent more likely to suffer with depression.
The report said: 'This study showed, for the first time, that aspirin is associated with a significantly lower risk of depression among older men with high homocysteine.'
Researchers say it is still not clear how homocysteine makes someone more susceptible to depression, but the men with high homocysteine who took a daily aspirin saw their risk of depression drop 43 per cent.
Taking vitamin B supplements, which can also lower homocysteine, did not have the same effect. US scientists recently discovered daily aspirin users are 16 per cent less likely to die if they develop any type of cancer.
Other studies suggest the drug can also cut the risk of prostate cancer by almost 30 per cent and bowel cancer by up to 60 per cent.
However aspirin can cause stomach bleeding in around one in a thousand patients.
Emer O’Neill, chief executive of the Depression Alliance, said although the research was ‘interesting’, patients should not change their treatment because of the findings.