EMBARGOED FOR RELEASE UNTIL 4 PM ET, February 22, 2017
MINNEAPOLIS – Sleeping more than nine hours a day may be an early sign of degeneration of the brain and signify an increased risk of dementia in older people, according to a new study published in the February 22, 2017, online issue of Neurology®, the medical journal of the American Academy of Neurology. “We found that when older people transitioned from regularly sleeping less than nine hours to sleeping more than nine hours, they had an increased risk of developing dementia 10 years later,” said study author Sudha Seshadri, MD, of Boston University School of Medicine in Boston, Mass., and Fellow of the American Academy of Neurology. “We also showed that those who had regularly slept more than nine 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, Mass., spanning two 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, or 10 percent, developed some form of dementia, and 181 of those, or 8 percent overall, were specifically diagnosed with Alzheimer’s disease. A total of 96 people, or 4 percent, reported sleeping more than nine hours a night at the beginning of the study and 75 people, or 3 percent, reported changing from sleeping nine or less hours to more than nine hours. Overall, those who slept more than nine hours were twice as likely to develop dementia than those who slept nine hours or less. Of the 96 people who reported sleeping more than nine hours, 19 developed dementia, or about 20 percent, compared to 215 of the 2,361 people who slept nine hours or less, or about 9 percent. Those who transitioned from sleeping less than nine hours to nine hours or more had a nearly two and a half times greater risk of developing dementia, with 16 of the 75 people developing dementia. They were also two 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 nine hours a day for 13 years prior had no increased risk of dementia. Those who slept more than nine hours as opposed to six to nine 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 five years of aging,” Seshadri said. “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, which is a precursor to dementia. People with no high school diploma who slept more than nine hours were six 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 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. 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. The study was funded by the National Heart, Lung, and Blood Institute, the National Institute on Aging and the National Institute of Neurological Disorders and Stroke. To learn more about dementia, visit www.aan.com/patients.
The American Academy of Neurology is the world's largest association of neurologists and neuroscience professionals, with 32,000 members. The AAN is dedicated to promoting the highest quality patient-centered neurologic care. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as Alzheimer's disease, stroke, migraine, multiple sclerosis, concussion, Parkinson's disease and epilepsy.