Vitamin B supplements offer no benefits in protecting the brain from ageing or Alzheimer’s disease, according to a new analysis.
The finding is the latest to suggest that special vitamin B tablets offer limit health benefits.
Two kinds of vitamin B, folic acid and B12, reduce levels of the chemical homocysteine in the body.
As high levels are found in people with Alzheimer’s disease, it had been suggested that vitamins could protect against the disease.
Researchers at Oxford University, UK, analysed 11 trials involving some 22,000 people to reach their conclusions, published in the American Journal of Clinical Nutrition.
Researcher Professor Robert Clarke said: "It would have been very nice to have found something different. Our study draws a line under the debate: B vitamins don’t reduce cognitive decline as we age.
"Taking folic acid and vitamin B12 is sadly not going to prevent Alzheimer’s disease."
He added: "Taking supplements like B vitamins doesn’t prevent heart disease, stroke or cognitive decline.
"About 25% of the adult population take multi-vitamins, often with the idea that they are also good for the heart or the brain, but the evidence just isn’t there. Much better is to eat more fruit and vegetables, avoid too much red meat and too many calories, and have a balanced diet."
Dr Simon Ridley, of Alzeimer’s Research UK, said he had hoped that a means of preventing the disease might be found.
He said: "Although one trial in 2010 showed that for people with high homocysteine, B vitamins had some beneficial effect on the rate of brain shrinkage, this comprehensive review of several trials shows that B vitamins have not been able to slow mental decline as we age, nor are they likely to prevent Alzheimer’s.
"While the outcome of this new and far reaching analysis is not what we hoped for, it does underline the need for larger studies to improve certainty around the effects of any treatment."
He added: "Research to understand how to prevent Alzheimer’s must continue, and in the meantime evidence shows that a number of simple lifestyle changes can help reduce the risk of the disease."
But Dr James Pickett, of the Alzheimer’s Society, said it was still possible the vitamins could help some people.
He said: "We need to see significantly more investment and recruit the next generation of leaders in research in order to deliver breakthroughs that could prove so vital to those affected by the condition."
Effects of homocysteine lowering with B vitamins on cognitive aging: meta-analysis of 11 trials with cognitive data on 22,000 individuals. American Journal of Clinical Nutrition 15 July 2014; 100:657-66 [abstract]
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