The correlation also held whether people were on sleep medications and whether or not they had a mutation called ApoE4 that makes people more likely to develop Alzheimer’s disease, Dr. Sabia said.
“The study found a modest, but I would mention a somewhat important association of short sleep and dementia risk,” said Pamela Lutsey, associate professor of epidemiology and community health at the University of Minnesota, who was not involved in the study. “Short sleep is very common and therefore, even if modestly associated with dementia risk, it can be important on a societal level. Short sleep is something we can control, something you can change. “
Still, as with other research in this area, the study had limitations that prevented it from proving that insufficient sleep can cause dementia. Most sleep data was self-reported, a subjective measure that’s not always accurate, experts said.
At one point, nearly 4,000 participants had sleep duration measured by accelerometers, and that data was consistent with their self-reported sleep times, the researchers said. Still, that quantitative measure came late in the study, when the participants were about 69, making it less useful than if it had been obtained at a younger age.
In addition, most of the participants were white and better educated and healthier than the overall UK population. And by relying on electronic health records for dementia diagnoses, researchers may have missed a few cases. They also couldn’t identify exact types of dementia.
“It’s always hard to know what to conclude from these kinds of studies,” wrote Robert Howard, a professor of old-age psychiatry at University College London, one of the many experts who submitted comments to Nature Communications on the study. “Insomniacs – who probably don’t need anything else to worry about in bed,” he added, “don’t have to worry about being on the road to dementia unless they fall asleep immediately.”
There are compelling scientific theories as to why too little sleep can increase the risk of dementia, especially Alzheimer’s. Studies have shown that amyloid levels in cerebrospinal fluid, a protein that clumps into plaques in Alzheimer’s disease, “go up when you rob people of sleep,” said Dr. Music. Other studies of amyloid and another Alzheimer’s protein, tau, suggest that “sleep is important for removing proteins from the brain or limiting production,” he said.