On the other hand, a high body-mass index (BMI) and poor heart health are significant risk factors for age-related dementia, the researchers said. BMI is an estimate of body fat based on height and weight.

The study included 1,260 people in Finland, aged 60 to 77, who were considered to be at high risk for dementia.

They were randomly selected to receive either regular health advice (the control group) or to be part of an intervention group.

Over two years, those in the intervention group met regularly with doctors, nurses and other health professionals who provided advice on:
 

After two years, those in the intervention group scored 25 percent higher overall on a standard test of mental function than those in the control group, according to the study in the March 12 issue of The Lancet.

The differences were much greater on some parts of the test. For example, people in the intervention group scored 150 percent higher in mental processing speed, and 83 percent higher in executive functioning, which is the ability to organize and regulate thought processes.

"Much previous research has shown that there are links between [thinking] decline in older people and factors such as diet, heart health and fitness. However, our study is the first large randomized, controlled trial to show that an intensive program aimed at addressing these risk factors might be able to prevent decline in elderly people who are at risk of dementia," study leader Miia Kivipelto, a professor at the Karolinska Institute in Stockholm, Sweden, said in a journal news release.

The researchers plan to follow the seniors for at least seven years to determine if the slower mental decline seen among those in the intervention group results in a reduced risk of Alzheimer's disease and other types of dementia.

While the researchers found a link between a healthy lifestyle and age-related dementia, they didn't prove cause and effect.