Exercise is associated with a slower progression of dementia in some seniors, according to new research, providing a further indication of the likely benefits of physical activity in the later stages of life.

Doctors in Europe studied 638 people aged 65 to 84 whose brains showed some early warning signs of dementia, but who reported no actual debilitation in their day-to-day activities.

Past studies are mixed on whether exercise reduces or increases the risk of dementia in seniors. (Associated Press)

The study subjects were followed over a three-year period, during which time they had their brains periodically scanned, were assessed for cognitive ability and reported how much exercise they did.

The researchers found that among the vast majority of the patients, there was a negative correlation between the amount of exercise they were doing at the outset of the study and whether they ended up with signs of dementia or cognitive decline by the end of the study.

The association was at its strongest for vascular dementia, a type of non-Alzheimer's dementia caused by problems of blood flow to the brain. The researchers found that exercise was associated with a more than 50 per cent lower rate of vascular dementia.

The findings didn't hold for the 34 research subjects who showed signs of Alzheimer's. In their cases, exercise had no correlation to their rates of mental decline.

And the results don't necessarily apply to all people of the study's age group because only individuals with some early physiological signs of dementia known as "white matter changes" were included as subjects. White matter changes can be found in anywhere from five per cent to 90 per cent of elderly people, depending on the study.

The study authors don't posit an explanation for their results, but they do caution that their correlation study can't necessarily be deemed to show a causal effect. It's possible that the relationship goes the other way: that people exercised less because they were suffering from cognitive impairment, for instance.

The researchers note that previous studies have cut both ways, with some suggesting exercise correlates to a decreased risk of Alzheimer's and other forms of dementia, and others saying the opposite.

The findings, which will be published in the December edition of the scientific journal Stroke, were released Thursday.