The blue colour shows where the brain tissue has shrunk by more than 1 mm. (Courtesy David Smith)

Elderly people who have higher levels of vitamin B12 in their blood may gain some protection against brain shrinkage, a new study suggests.

The brain normally shrinks about 0.5 per cent per year in normal elderly brains, compared with 1 per cent in those with mild cognitive impairment and 2 per cent in the same time for those with Alzheimer's, said the study's lead author, pharmacology Prof. David Smith of the University of Oxford in Britain.

In Tuesday's issue of the journal Neurology, Smith and his colleagues report that people in the upper third of vitamin B12 levels were six times less likely to experience brain shrinkage compared with those who had the lowest levels.

All 107 participants in the study were between the ages of 61 and 87 and were not deficient in vitamin B12 based on usual criteria. The subjects had scans to measure the volume of their brains, as well as memory tests and physical exams including blood tests to assess their B12 levels once a year for up to five years.

"We can only advise that it makes good sense to eat plenty of the foods that are a good source of B12, such as fish, milk (low-fat is fine) and meat and, in North America, fortified breakfast cereals," Smith said in an e-mail interview.

The team is carrying out a trial of B vitamins in elderly people with memory imp

'It is the first time that something in the blood which is related to our diet has been shown to be related to brain shrinkage.'— Prof. David Smith

airment to see if the vitamins can slow the rate of brain shrinkage.

The results are expected in 2009.

While the latest results suggest that modifying B12 might protect the brain and possibly prevent cognitive decline, the researchers cautioned the findings to date do not prove a benefit.

"Many factors that affect brain health are thought to be out of our control, but this study suggests that simply adjusting our diets …may be something we can easily adjust to prevent brain shrinkage and so perhaps save our memory," agreed study author Anna Vogiatzoglou, also at Oxford.

Smith and Vogiatzoglou used a more accurate way of testing for vitamin B12 compared with previous studies that showed mixed results.

"The result is novel as it is the first time that something in the blood which is related to our diet has been shown to be related to brain shrinkage," Smith said.

Vitamin B12 helps in the formation of red blood cells and is important to help maintain the central nervous system.

A full-blown deficiency of vitamin B12 is rare in developed countries, but elderly people may not absorb it well and vegetarians may not get enough from their diet.

Vitamin B12 deficiency is a serious problem in less developed countries such as India. Deficiency can lead to anemia and neurological damage.