Keeping active can reduce the risk of Alzheimer's disease even in people over the age of 80, a 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 and thinking ability. 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 Aron Buchman, from Rush University Medical Center in Chicago, said: "The results of our study indicate that all physical activities including exercise as well as other activities such as cooking, washing the dishes, and cleaning are associated with a reduced risk of Alzheimer's disease.
"These results provide support for efforts to encourage all types of physical activity even in very old adults who might not be able to participate in formal exercise, but can still benefit from a more active lifestyle."
The findings appear in the online issue of the journal Neurology.
Dr Anne Corbett, research manager at the Alzheimer's Society, said: "It is well established that regular physical exercise is an important way to reduce your risk of developing dementia.
"It can reduce the risk by up to 45%. This study adds to this evidence and suggests that simple things like cooking and cleaning can also make a difference.
"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. It is important to maintain a healthy weight and stop smoking.
"Eating a Mediterranean diet high in antioxidants and oily fish and even the odd glass of red wine can also help."
Dr Simon Ridley, head of research at the charity Alzheimer's Research UK, said: "There is already some evidence that exercise in mid-life can help to reduce the risk of Alzheimer's. This study adds to this by suggesting that daily physical activity like doing household jobs or playing cards could have benefits into older age.
"One of the strengths of this study is that physical activity was measured using a small monitoring device, rather than relying on self-reported questionnaires which can often be unreliable.
"While the study highlights an association between physical activity and cognitive decline, more research is needed to explore this relationship further."