New research suggests those who sleep for more than 9 hours each night are at a higher risk of developing 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."

Dr. Sudha Seshadri

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.

The authors believe the findings may inform future dementia and cognitive impairment detection practices. Co-corresponding author Matthew Pase, Ph.D., who is a fellow in the department of neurology at BUSM and investigator at the FHS, weighs in on the significance of the findings.

"Self-reported sleep duration may be a useful clinical tool to help predict persons at risk of progressing to clinical dementia within 10 years," he says. "Persons reporting long sleep time may warrant assessment and monitoring for problems with thinking and memory."

The sooner a patient is diagnosed with dementia, the more time they and their families have to plan ahead and make crucial healthcare decisions.