FEW people who have enjoyed tender imported asparagus, now in the shops, have thought that they were about to eat something with a role in treating depressive symptoms. Asparagus is not an immediate antidepressant like a good brisk walk, but it is rich in folic acid: a regular diet of this vitamin keeps blood folate levels high, homocysteine levels low and depression at bay. It is only one of many folate-rich foods, deprivation of which may play a part in depressing our mood.

Adequate folic acid taken before and during the first few months of pregnancy dramatically reduces the number of babies born with physical abnormalities. Among its many influences in adult medicine is its probable ability to help to reduce the incidence of both heart disease and Alzheimer’s.

Fortunately, not all foods rich in folic acid are as expensive and exotic as asparagus. Many of them can equally well be enjoyed in Brixton as Belgravia, since folic acid is also found in dark green vegetables, such as spinach, broccoli and even the ubiquitous Brussels sprout,which made school lunches such an ordeal.

Dark green vegetables and brightly coloured citrus fruits, including oranges and grapefruit, are not the only good sources of folates; yeast extract — including Marmite — is rich in this vitamin. One of the best but least-known sources of folic acid is chicken livers. They rank between yeast extract and beans as an excellent source. And folic acid is also found in abundance in the rather more ordinary lamb’s liver.

The recent report of research showing that regular, steady exercise is one of the most effective ways of keeping mild depression at bay is no surprise. The influence of food on mood is less well known. However, the effect on the psyche of chocolates — as well as some exotic plants such as St John’s wort, gingko biloba, ginger and ginseng — is well recorded.

A varied, well-balanced diet does not keep only the mind healthy by maintaining a healthy body: its individual constituents, including those that contain a plentiful supply of folic acid, may have a specific part to play in treating depression.

Over the past 25 years several surveys have revealed that the proportion of patients with depression who also have low folate levels is very high. And new research has shown that up to a third of patients with severe depression have folate deficiency. Dr Edward Reynolds and his team from the Department of Neurology at King’s College Hospital, South London, together with research workers from the Department of Psychological Medicine and the Department of Psychiatry at Northwick Park Hospital, believe that although folate deficiency in the depressed may be the result of a poor appetite and hence restricted diet, in others it could have contributed to the development of the depression.

The good news is that, whatever the sequence of events, the speed of recovery once the folate deficiency had been corrected was improved. The research workers have also shown that a very sensitive marker for the folate levels in the blood, and levels of vitamin B12, is the level of homocysteine. The higher the levels of homocysteine, the greater the folate deficiency.

Less well publicised is the influence of folic acid on a feeling of wellbeing, but that may be changed by the work of Dr Reynolds and his colleagues. Their study of the association between folic acid and depression has recently been published in the Journal of Neurology, Neurosurgery and Psychiatry.

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