NEW YORK: Middle-age people who sleep six or fewer hours a night may be at higher risk of developing dementia in later life, a major new study finds.
People age 50 or 60 who regularly slept six hours or less each night were more likely than those who slept seven hours to be diagnosed with dementia, according to the study published Tuesday in the scientific journal Nature Communications, which is headquartered in London, with an office in New York City.
Even after controlling for cardiac, metabolic and mental-health issues, the study researchers found that 50-year-olds who were sleeping six hours or less a night had a 22% higher risk of developing dementia later in life. Sixty-year-olds were 37% more likely to develop the disorder. The comparisons were with people who slept for seven hours each night.
The study does not prove that sleeping too little causes dementia, since sleep loss itself may be one of the earliest symptoms of the disease. But some scientists believe the results bolster evidence that persistent poor sleep may at least contribute to the neurodegenerative disease.
Researchers do not know whether improving sleep can reduce the risk of dementia, but sleep is known to clear toxic waste from the brain. One hypothesis is that when people sleep less, this process becomes impaired.
“These findings suggest that sleep duration might be a risk factor for dementia in later life,” said Dr Severine Sabia, an author of the study at the University of Paris. “I cannot tell you that sleep duration is a cause of dementia but it may contribute to its development.”
Sabia and her colleagues analyzed survey data from University College London’s Whitehall II study, which launched in 1985 and followed the health and lifestyles of more than 10,000 British volunteers. The French team focused on nearly 8,000 participants who self-reported their sleep patterns, although some wore watch-like devices to confirm how long they slept.
During 25 years of follow-up, 521 participants developed dementia, with most diagnosed in their late 70s. Writing in Nature Communications, the scientists described how those who routinely got six hours of sleep or less each night in their 50s and 60s were 30% more likely to develop dementia than those who typically managed seven hours.
The findings came after an international team reported on Monday that severely disrupted sleep could nearly double women’s risk of dying from heart disease, when compared with the general female population.
The study, in the European Heart Journal, found the risk for men increased by about a quarter. Body mass index and sleep apnoea, which disrupted breathing, both contributed to “unconscious wakefulness”, while disrupting the body’s natural circadian rhythms could drive the buildup of fat in arteries that could lead to cardiovascular problems.
While smoking, heavy drinking and obesity are risk factors for dementia, the chances of developing the disease rise steeply with age. Dementia is estimated to affect one in 14 over-65s and one in six people aged over 80. The risk of developing Alzheimer’s or vascular dementia doubles roughly every five years above the age of 65.
The first pathological changes that lead to dementia occur one to two decades before the disease becomes obvious, as sticky proteins called amyloid and tau build up in the brain. When the 1985 Whitehall II study first assessed the sleep of volunteers who later developed dementia, this process had probably not started. This meant that if they were sleeping too little, it was unlikely to have been caused by dementia-related brain changes.

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