For a fortunate group, exercise and the right diet could protect against cognitive symptoms that develop with age.

A healthy lifestyle might reduce the risk of dementia — but not in people with a high genetic predisposition to the condition.

Although the exact causes of dementia are unclear, scientists think that both genetics and lifestyle have a role. Silvan Licher and Kamran Ikram at Erasmus University Medical Center in Rotterdam, the Netherlands, and their colleagues examined the incidence of dementia in 6,352 Dutch people aged 55 and older who were part of a long-term study. The researchers grouped participants according to the presence of genetic variants that increase the risk of dementia.

In 15 years, 14.4% of participants developed dementia. Among the individuals with a low or intermediate genetic predisposition, those who ate a healthy diet, abstained from smoking, were physically active, did not have depression or diabetes and were not socially isolated had a reduced risk of developing the condition. But a favourable profile wasn’t associated with a lower dementia risk in people who had a high genetic predisposition to the disease.

The findings could help to improve the design of dementia-prevention trials, the researchers say.