A study from the University of Oxford showed how the brains of patients taking folic acid, vitamin B6 and B12 shrank at a lower rate than those on placebo.

The researchers suggested vitamin treatment may slow the development of Alzheimer’s disease, which has been linked to brain shrinkage.

The B vitamins in the study are known to control levels of homocysteine in the blood, also associated with an increased risk of Alzheimer’s.

In the study, all participants were over 70 years old with mild cognitive impairment.

Those in the intervention group were given a daily supplement containing folic acid (0.8mg/day), vitamin B12 (0.5mg/day) and vitamin B6 (20mg/day). The control group was given a placebo tablet.

Researchers found the brains of those on supplements shrank at an average annual rate of 0.76%, while those of the control group shrank 1.08% per year.

Rebecca Wood, chief executive of the Alzheimer’s Research Trust, which co-funded the study, said: ‘These are very important results, with B vitamins now showing a prospect of protecting some people from Alzheimer’s in old age.

‘The strong findings must inspire an expanded trial to follow people expected to develop Alzheimer’s, and we hope for further success.’

Chris Kennard, chair of the Medical Research Council’s Neurosciences and Mental Health Board, which co-funded the study, said: ‘This MRC-funded trial brings us a step closer to unravelling the complex neurobiology of ageing and cognitive decline, which holds the key to the development of future treatments for conditions like Alzheimer’s disease.

‘The findings are very encouraging and we look forward to further research that is needed in order to test whether B Vitamins can be recommended as a suitable treatment.’