Researchers have found that older adults who get only short periods of sleep each night may be at increased risk of dementia or earlier death.

In a study of 2,600 older Americans, researchers found that those who were categorized as “short sleepers” (with no more that five hours of sleep at night) were more likely to develop dementia or die over the next five years. Their risks were double those of older adults who typically got the recommended seven to eight hours of sleep.

The new study, recently published in the journal Aging, is not the first to associate poor sleep with disquieting health outcomes, including dementia. But this study has focused on a particularly troublesome problem, according to Rebecca Robbins, PhD, an associate scientist in the division of sleep and circadian disorders at Brigham and Women’s Hospital in Boston. “We looked at a series of sleep characteristics, which allowed us to ask what matters most,” she said.

“The resounding answer was short sleep.” That mattered to study participants more than self-rated sleep quality or whether it took a long time to fall asleep at night, or whether they were likely to feel groggy or in need of a nap during the day. Additionally, researchers found that short sleep appeared more important than snoring. A sign of obstructive sleep apnea, chronic snoring has been linked to both heart disease and dementia. However, the research findings fail to prove that short sleep itself helps to cause dementia or reduce the length of lives.

“It may be that in some cases, the poor sleep is actually an early sign of dementia, rather than a cause,” said Sabra Abbott, MD, an assistant professor of neurology At Northwestern University’s Feinberg School of Medicine in Chicago. She was not involved in the study but suggested that sleep can be disrupted for multiple reasons early in the dementia process. She noted that a brain structure called the suprachiasmatic nucleus, which helps regulate the timing of sleep and production of the sleep hormone melatonin, can begin to degenerate early in the course of dementia.

Because dementia itself can cause sleep issues, Robbins and her colleagues attempted to account for that, excluding older adults who already had dementia at the start of the study. Additionally, they statistically accounted for other health conditions participants had, such as heart disease, diabetes, high blood pressure and depression symptoms.

Findings indicated that short sleep was still linked to a twofold increase in the risk of dying or developing dementia during the study period. Over the course of five years, 321 participants of 2,610 American older adults aged 65 and older screened positive for dementia. More than one-half of participants reported getting seven to eight hours of sleep each night. About 4% said they got five hours or fewer.

Robbins said there are reasons to believe that sleep deprivation can damage the brain. Animal research has shown that adequate sleep may be critical to the brain’s clearing of abnormal proteins associated with Alzheimer’s disease. She said that generally, it’s difficult to know whether poor sleep helps cause the brain disease or is part of its manifestation.

If you are experiencing difficulties with falling asleep at night or staying asleep, it’s important to consult your provider for a medical evaluation. There may be an underlying cause for sleep problems, such as medications or sleep apnea.

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