PETER LLOYD: An Australian dementia expert is saying that new evidence from the United States shows the importance of a healthy lifestyle in preventing dementia.

A study of more than 2,000 people shows that high blood-sugar levels are a risk factor for the condition.

It was already known that dementia was linked with diabetes, but this study shows that sugar can have a detrimental effect on the brain far earlier than previously thought.

Simon Lauder reports.

SIMON LAUDER: Associate Professor of Internal Medicine at the University of Washington, Paul Crane, examined blood sugar readings taken over many years from more than 2,000 people aged over 65.

They didn't have dementia when the study began, but 524 of them developed it.

PAUL CRANE: Higher blood-sugar levels are indeed a risk factor for dementia, so that was not something that had been appreciated previously. We had known for some time that it looks like diabetes itself was associated with dementia. On average, people with diabetes have higher blood-sugar than people who don't have diabetes.

So we were looking both among people with diabetes and people who didn't have diabetes. The thing that's especially newsworthy about our finding was that we found this association between blood-sugar and dementia risk even among people who had very normal levels of blood-sugar - not particularly elevated and certainly not in the diabetes range.

SIMON LAUDER: The national research manager with Alzheimer's Australia, Dr Chris Hatherly, says the study confirms earlier suspicions that higher blood-sugar is related to an increased risk of dementia.

CHRIS HATHERLY: There was some Australian research last year which showed that high blood-sugar in a middle-aged sample of people over time was related to increased shrinkage of the brain.

So people with higher blood-sugar actually losing brain cells. and this study here is showing now that that's related to an increased risk of dementia. So it's very significant, it adds to what we know and it basically concerns that in maintaining a healthy lifestyle and a healthy diet are really vital for people if they want to reduce their risk of developing dementia.

SIMON LAUDER: We hear a lot about type-2 diabetes being a lifestyle disease. Do you think it does raise the question of whether dementia to some extent is also a lifestyle disease?

CHRIS HATHERLY: Well, I mean there is a lifestyle factor that relates to dementia but certainly it's not a lifestyle disease, you know we have people who have absolutely healthy lives, never smoked, rarely drink, have very healthy diets, lots of exercise who still develop dementia.

So unfortunately you know it's not strong enough to be able to say that if people do have a healthy lifestyle they will definitely not develop dementia but it is related to the risks, we definitely know that.

SIMON LAUDER: Researchers are yet to work out why sugar is a dementia risk factor. Professor Crane warns against jumping to conclusions.

PAUL CRANE: We're not trying to alarm anybody or make anybody super changing their behaviours or anything like that. Instead what we're finding is an association that's very interesting and that should make us perhaps change the way we think about the interactions between blood-sugar and the brain.

But this was a small effect. In any case what we know is that we found an association which is very different than finding causation. So there's a lot of work that needs to be done before we make those sorts of conclusions.

SIMON LAUDER: The findings are published in the New England Journal of Medicine.

PETER LLOYD: Simon Lauder.