KEEPING active can reduce the risk of Alzheimer's disease even in people over the age of 80, a US study has found.

Researchers asked 716 volunteers with an average age of 82 to wear a device that monitors day-to-day activity. Study participants were also given cognitive tests to measure memory.

After around three years, 71 of the volunteers developed Alzheimer's disease.

The research showed that the least active were more than twice as likely to develop the disease as those who were most active.

Dr Anne Corbett, research manager at the Alzheimer's Society, said: "One in three people over 65 will die with dementia, but as this shows, there are things you can do to help reduce your risk."