NEW YORK (Reuters Health) – Older adults whose vitamin B12 levels are low but within the normal range may have a quicker rate of brain shrinkage as they age, researchers reported Monday.

In a study of 107 adults older than 60, British researchers found that those whose vitamin B12 stores were relatively low showed a greater rate of brain atrophy over the next five years. Such brain-volume loss has been linked to a faster rate of mental decline and progression to Alzheimer’s disease in older adults.

Vitamin B12 is vital for maintaining healthy nerve cell, and overt deficiency in the vitamin can damage the nervous system, the investigators point out in their study, published in the journal Neurology.

None of the healthy older adults in the current study were deficient in B12, however. Instead, those will B12 blood levels that were normal but low, compared with the other study volunteers, showed a greater rate of brain atrophy on MRI scans.

The findings do not prove that lower B12 stores in older adults cause brain shrinkage. But they do indicate that lower levels of the vitamin are a marker, or sign, of brain atrophy — and possibly a modifiable risk factor for cognitive decline, explained lead researcher Dr. Anna Vogiatzoglou, of the University of Oxford.

“Our study suggests, but does not prove, that by modifying our vitamin B12 status we might be able to protect our brain and so possibly prevent cognitive decline,” Vogiatzoglou told Reuters Health.

She and her colleagues recruited 107 dementia-free, well-functioning adults between the ages of 61 and 87 for the study. At the outset, the volunteers underwent MRI brain scans, memory tests and blood tests to measure their B12 levels. Five years later, they had another MRI scan.

The one third of volunteers who showed the greatest brain-volume loss over the study period was considered to have an increased rate of brain atrophy. Those who’d had the lowest B12 levels at the outset were six times more likely than other study participants to fall into this category.

It’s too early to advise older adults to take supplements of B12 for the sake of slowing brain shrinkage, Vogiatzoglou said. That, she noted, awaits the results of a clinical trial she and her colleagues are currently conducting to see whether a combination of B vitamin supplements affects brain volume in older adults with memory problems.

“What we can say,” Vogiatzoglou added, “is that our results suggest that rather than maintaining one’s B12 at a level that is just above the cut-off for deficiency, it might be prudent to aim to keep it higher up the normal range.”

This, she said, can be done by eating foods naturally rich in B12 — such as lean meat, fish and milk products — as well as fortified breakfast cereals. The recommended dietary allowance for B12 in adults is 2.4 micrograms per day.

SOURCE: Neurology, September 9, 2008.