According to a recent study, which was published in the JAMA Neurology, people who sleep more than nine hours or less than six hours a night are at higher risk of Alzheimer’s disease.
For the study, researchers at Stanford University School of Medicine looked at 4,417 men and women who aged between 65-85 years old. They were cognitively healthy, with no signs of Alzheimer’s disease, and participated in the Anti-Amyloid Treatment in Asymptomatic Alzheimer’s Disease (A4) study, which is being conducted in the Australia, Canada, Japan, and United States.
All of the participants had underwent PET brain scans and filled out detailed questionnaires about their sleep habits, including how many hours of sleep they typically got at night and how often they napped during the day.
The researchers found that those men and women who typically slept six or fewer hours a night scored lower on tests of memory function, compared to those who got the normal seven or eight hours a night. They also had higher levels of beta-amyloid buildup in their brains. High levels of beta-amyloid are associated with an increased risk of developing Alzheimer’s disease.
They also found that those who slept more than nine hours a night tended to score lower on tests of memory and thinking skills, though there was no difference in beta-amyloid levels between the long and normal sleep duration groups.
In addition, both the short and the long sleepers are more likely to have a higher body mass index when compared to those normal sleepers. A high BMI indicates being overweight or obese, which is a risk factor for Alzheimer’s disease and other forms of dementia.
In other study published in Alzheimer’s & dementia, researchers analyzed data from 7,444 women aged between 65 and 80 years. They identified 802 women with significant cognitive decline, including 368 with mild cognitive impairment and 265 with dementia.
They then compared sleep duration in women with and without cognitive decline. They found a 36 percent increased risk of cognitive decline in women who reported sleeping six or fewer hours a night and a 35 percent increased risk in those who reported slept longer than eight hours.
And in yet another study conducted by researchers at Brigham and Women’s Hospital in Boston found that those who slept fewer than five hours per day or more than nine hours per day had worse cognitive function than those who slept seven hours per day.
That study included 15,385 women aged over 70, whose brain functioning was first analyzed sometime between 1995 and 2000. The researchers continued to analyze their brain functioning every two years for a total of six years, and found that women who slept for more or fewer than seven hours per day had changes in brain functioning that were similar to aging two years. It can cause accumulation of beta-amyloid in the brain—a hallmark Alzheimer’s disease pathology.
However, it’s important to note that all of this research only notes a link, not a cause. But it suggests that if you aren’t sleeping well, you should talk to your doctor.