A vitamin used to lower the risk of birth defects may also be an effective treatment for depression.
Research shows that men with high levels of folate in their diets were up to 50 per cent less likely to have symptoms of depression than those with the lowest amounts.
Now a £1million clinical trial is under way in Britain looking at whether giving folate can help tackle the condition by boosting the effects of drug treatment.
Folate, one of the B vitamins, is found naturally in some foods, including leafy vegetables, beans, citrus fruits and wholegrains. As a supplement, folic acid - the synthetic form of the vitamin - has been shown to be effective in reducing the risk of birth defects. Research shows it can lower the chances of neural tube defects, including spina bifida, where the spine is incorrectly developed, by up to 70 per cent. The vitamin is involved in the process of making healthy new cells. Both adults and children need folate to make normal red blood cells and prevent anaemia.
One in five people experience depression at some point, but scientists say only half of those treated with antidepressants will get better; and many others experience symptoms for long periods. Now researchers have found that the more folate in the diet, the less severe the symptoms of depression.
Symptoms can include low mood, irritability, loss of selfconfidence, lack of energy, insomnia and low libido.
A study by the National Institute of Health and Nutrition in Japan found that men with the highest folate levels had 50 per cent fewer symptoms of depression compared to those with the least amounts in their diets.
A second study, at the Centre de Recherche de Jouyen- Josas, in France, found folate protected against recurrent bouts of depression in men over an eight-year period.
A third study, at the University of Kuopio, in Finland, based on 2,682 men aged 42 to 60, found that those with the lowest levels of folate had a 67 per cent higher risk of being depressed than those who had the highest.