People who sleep longer twice as likely to develop dementia

Over 46 million people are living with dementia worldwide, and the number is expected to almost triple by 2050.

In the United States, over 5 million people are currently estimated to have Alzheimer's disease. The disease risk increases with age, as 1 in 3 seniors die with Alzheimer's or another form of dementia.

The financial burden of the disease is also great. American families are believed to spend over $5,000 yearly on caring for someone with Alzheimer's, and the national economic burden is estimated at $236 billion.

A new, large-scale study suggests people with prolonged sleeping patterns may have an increased risk of developing dementia.

The research was led by Dr. Sudha Seshadri, professor of neurology at Boston University School of Medicine (BUSM), and the findings were published in the journal Neurology.

Researchers examined data from the Framingham Heart Study (FHS). FHS is a large cohort study that started in 1948 by enrolling 5,209 men and women aged between 30 and 62 living in the town of Framingham, MA. The original purpose of the study was to identify risk factors for cardiovascular disease.

Sleeping 9 hours or more linked to greater dementia risk
For this study, a large number of adults enrolled in the FHS were asked to report how long they usually slept per night. The researchers then clinically followed the participants for 10 years to see who developed Alzheimer's disease and other forms of dementia.

BUSM researchers then examined the data collected on sleep duration and calculated the risk of developing dementia.

The team found that people who sleep regularly for 9 hours or more were twice as likely to develop Alzheimer's within 10 years, compared with those who consistently slept less than 9 hours.

Additionally, as the study's lead author explains, education seems to be playing a role in staving off the risk of dementia.

"Participants without a high school degree who sleep for more than 9 hours each night had six times the risk of developing dementia in 10 years as compared [with] participants who slept for less. These results suggest that being highly educated may protect against dementia in the presence of long sleep duration."

The study also found that people who slept longer seemed to have smaller brain volumes. Being observational, the study cannot establish causality, but the researchers suspect excessive sleep is probably a symptom rather than a cause of the neuronal changes that come with dementia. As a consequence, they speculate, reducing sleep duration is not likely to lower the risk of dementia.