Losing memory as you age may not be inevitable, according to U.S. research which suggests that maintaining low blood sugar levels through diet and exercise may keep memories intact longer.

The study, by the New York University School of Medicine in the U.S., found that subjects who scored lowest on memory recall tests also had poor glucose tolerance, and tended to have a significantly smaller hippocampus - the part of the brain responsible for learning and memory. This is the first time the association has been seen.

"We have demonstrated that impaired glucose regulation is associated with memory dysfunction and shrinkage of the hippocampus," said Associate Professor Antonio Convit, medical director of the Centre for Brain Health, who led the study.

"It raises the intriguing possibility that improving glucose tolerance could reverse some age-associated problems in cognition," he said.

The results are published in the latest issue of the journal, Proceedings of the National Academy of Sciences.

The study involved 30 men and women who were middle-aged to elderly, and did not have diabetes, although some subjects had a less severe form of blood sugar increase called impaired glucose tolerance (IGT).

The prevalence of IGT rises with age, so Convit and colleagues were trying to establish if having IGT affects memory function in healthy people.

Diabetes has been linked with memory impairments, and it is thought that the condition reduces the ability to get glucose from the blood to the tissues where it is broken down to do useful work. Human brains use glucose almost exclusively as a fuel source.

The researchers found that the people with IGT had a smaller hippocampus and scored worse on tests for recent memory. The hippocampus is especially vulnerable to injury, and the researchers speculate that an inadequate sugar supply may cause it to atrophy over time.

"What is surprising is that the impact seems to be restricted to the hippocampus, as no associations were found to the volume of other brain regions, including a measure of overall brain atrophy," the authors write in their paper.

Subjects were given glucose intravenously and the researchers assessed how quickly the glucose moved from the blood to the tissues - a measure of glucose tolerance. They were then tested for their overall cognitive function and ability to recall short paragraphs.

The implications of the work could be far reaching, as 25 per cent of those over 65 years have sufficient cognitive problems which are short of dementia but still affect the quality of their lives, the researchers said.

It is possible to maintain healthy glucose tolerance through diet and exercise, they added.

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