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Can folic acid help prevent stroke?

Q Is folic acid a worthwhile preventive treatment following a stroke?

A The role of supplementary intake of folate in reducing the risk of stroke has been under investigation following the emergence of evidence linking homocysteine in plasma to the risk of cerebrovascular disease.

Homocysteine is an amino acid which is a normal constituent of the diet and is found in circulating blood. Folate is a vitamin that regulates the metabolism of homocysteine in the body. Studies in vivo have shown an inverse relationship between folate and homocysteine levels in the blood.

Randomised control trials have also demonstrated that levels of homocysteine in the blood can be reduced by dietary folate supplementation.

It has been postulated that dietary intake of folate may reduce the risk of stroke due to its effects on homocysteine. An inverse relationship between dietary folate intake and the risk of stroke has also been reported in epidemiological studies.

A large prospective cohort of a US population was followed up over 19 years for the incidence of stroke. This showed patients whose dietary intake of folate was at least 300µg were about 20 per cent less likely to suffer a subsequent stroke compared with those whose daily diet contained less that 136µg.

Definitive randomised controlled clinical trials are under way to establish whether increased intake will reduce incidence of stroke. Until these are complete, folate treatment is unproven.

But dietary intake of 300-400µg can be used safely for patients at risk of stroke. It is recommended to check vitamin B12 levels before prescribing, as folate can unmask complications in vitamin B12-deficient patients.

Dr Bridget Macdonald is consultant neurologist at the Mayday University Hospital, Surrey, and St George's NHS Trust, London, and Dr Zaitun Ahmed-Jushuf is an SHO in neurology at St George's

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