Recent study indicated that people who sleep for more than eight hours or enjoy afternoon nap are at higher risk of developing Alzheimer's. Over-sleeping nearly doubles the risk of Alzheimer's.

The reason behind association between the over-sleeping and the increased Alzheimer's risk is not yet clear. But researchers believe that by keeping a track of the sleeping hours of their patients, doctors can predict the onset of Alzheimer's.

Experts at the University Hospital of Madrid in Spain analyzed data collected from 3,286 men and women aged 65 or over. The study subjects were asked about their health, lifestyle and sleeping hours in day.

The study subjects were followed for more than three years. During study span 140 study subject developed Alzheimer's or another form of dementia.

Data analysis revealed that those who slept for more than eight or nine hours of sleep on average in a day were twice as likely to develop dementia.

The researchers said: 'We found a significant association between long sleep duration and dementia. Long sleep may be an early symptom of dementia, or could lead to an increased risk of it.'