High doses of selected B vitamins may significantly slow the rate of brain shrinkage in elderly people suffering from mild mental decline, say British researchers.

Roughly one in six people over the age of 70 has a mild cognitive impairment, but not so that it interferes with daily life. However, about half of those with mild cognitive impairment do go on to develop dementia — mainly Alzheimer's disease — within five years of diagnosis.

Results of a randomized two-year clinical trial released Thursday suggest taking a treatment of folic acid, vitamin B6 and B12 can halve the rate of brain shrinkage.

"It is our hope that this simple and safe treatment will delay the development of Alzheimer's disease in many people who suffer from mild memory problems," David Smith of the department of pharmacology at Oxford University and co-leader of the trial, said in a release.

The study, published in journal PLoS ONE, followed168 volunteers aged 70 or over with mild memory problems. Half the participants took high dose B vitamin tablets for two years while the other half took placebos.

Researchers have known for some time that certain B vitamins — folic acid, vitamin B6 and vitamin B12 — control levels of the amino acid homocysteine in the blood, and that high levels of homocysteine are associated with an increased risk of Alzheimer's.

The Oxford researchers wanted to know whether supplements of the B vitamins that lower homocysteine could also slow the higher rate of brain shrinkage seen in those with mild cognitive impairment or Alzheimer's disease.

The researchers found that, on average, the brains of those taking the B vitamin treatment shrank at a rate of 0.76 per cent a year. Those taking a placebo experienced brain shrinkage at a rate of 1.08 per cent.

People with the highest levels of homocysteine to start with benefited most, showing brain shrinkage rates that were half of those on placebo.

Could slow Alzheimer's

The researchers also examined cognitive test scores, revealing that those with the slowest rate of shrinkage scored the best.

The team suggests that, since brain shrinkage happens faster in those with mild cognitive impairment who go on to develop Alzheimer's, it is possible that the vitamin treatment could slow down the development of the disease.

Clinical trials could confirm this possibility, they say.

"These are immensely promising results, but we do need to do more trials to conclude whether these particular B vitamins can slow or prevent development of Alzheimer's," said Smith. "So I wouldn't yet recommend that anyone getting a bit older and beginning to be worried about memory lapses should rush out and buy vitamin B supplements without seeing a doctor."

There are just under half a million people in Canada with dementia — including Alzheimer's disease — with more than one million expected to have dementia by 2038, says the Alzheimer Society of Canada.

According to the researchers, their study is the largest to examine the effect of B vitamins on mild cognitive impairment, and one of the first disease-modifying trials to show positive results in those with Alzheimer's disease.