Getting the right amount of sleep each night could play a key role in reducing dementia risk, according to new research.

A team at York University in Canada pooled data from 69 previous studies. They found that seven to eight hours of sleep a night was the sweet spot for minimising dementia risk.

Sleeping less than seven hours was linked to an 18 per cent increase in dementia risk. Sleeping more than eight hours was linked to a 28 per cent increase.

The findings were published in the journal PLOS One. The analysis covered almost 4.5 million dementia-free adults.

Physical activity also mattered. People who exercised for at least 150 minutes a week had a 25 per cent lower risk of dementia.

Those who sat for more than eight hours a day faced a 27 per cent higher risk.

The researchers stressed that their review shows associations, not proof of cause. Sleeping too much could be an early sign that Alzheimer’s has already begun, rather than a driver of it.

“Regular physical activity, less sedentary time and appropriate nightly sleep may be associated with reduced risk of dementia,” the researchers wrote.