Sleeping more than 9 hours a day may be an early sign of degeneration of the brain and may signify an increased risk of dementia in older people, according to a study published in the February 22, 2017, online issue of Neurology.
“We found that when older people transitioned from regularly sleeping less than 9 hours to sleeping more than 9 hours, they had an increased risk of developing dementia 10 years later,” said Sudha Seshadri, MD, Boston University School of Medicine, Boston, Massachusetts. “We also showed that those who had regularly slept more than 9 hours in the past and simply maintained that level of sleep did not have an increased risk.”
For the study, researchers evaluated data on 2,457 people living in Framingham, Massachusetts, spanning 2 generations, who were regularly examined and surveyed about their health as part of a large, community-based study. The average age of participants was 72 years.
Over 10 years, 234 people (10%) developed some form of dementia, and 181 of those (8% overall) were specifically diagnosed with Alzheimer’s disease. A total of 96 people (4%) reported sleeping more than 9 hours a night at the beginning of the study and 75 people (3%) reported changing from sleeping 9 hours or less to more than 9 hours.
Overall, those who slept more than 9 hours were twice as likely to develop dementia than those who slept 9 hours or less. Of the 96 people who reported sleeping more than 9 hours, 19 developed dementia (~20%) compared with 215 of the 2,361 people who slept 9 hours or less (~9%).
Those who transitioned from sleeping less than 9 hours to 9 hours or more had a nearly 2.5 times greater risk of developing dementia, with 16 of the 75 people developing dementia. They were also 2 times more likely to develop Alzheimer’s disease, with 11 out of the 75 people developing Alzheimer’s disease.
People who had already been sleeping for more than 9 hours a day for 13 years prior had no increased risk of dementia.
Those who slept more than 9 hours as opposed to 6 to 9 hours also were less successful in processing thoughts and accomplishing tasks and had lower brain volume.
“The difference in scores on tests of processing thoughts was the equivalent of about 12 years of aging, and the difference in brain volume was the equivalent of about 5 years of aging,” said Dr. Seshadri. “These estimates are based on small numbers and are not precise, but they give you some context for the size of the difference between those who slept longer and those who did not.”
Those who slept longer were also more likely to have no high school diploma and mild cognitive impairment. People with no high school diploma who slept more than 9 hours were 6 times more likely to develop dementia.
“Together, these results suggest that if someone is sleeping longer, it may be an early marker of neurodegeneration,” said Dr. Seshadri. “Unfortunately, it is likely that any efforts to reduce their amount of sleep would not lower their risk of dementia.”
There were limitations of the study, including participants self-reported sleep data. In addition, researchers only looked at overall sleep totals and did not divide those totals into overnight sleep and naps. Further study is needed to better examine the biology behind longer sleep duration.
SOURCE: American Academy of Neurology