Why Sleeping Too Much May Be Bad for Mental Health

Sleep is a good indicator of our overall health and well-being. Seven to nine hours of sleep is recommended to feel truly rested, but oversleeping on a regular basis could signal problems with our brain health.

A study published in Neurology found people who consistently sleep more than nine hours a night are more likely to develop dementia accompanied by smaller brain volume and poor executive function.

“Participants without a high school degree who sleep for more than 9 hours each night had six times the risk of developing dementia in 10 years as compared to participants who slept for less," said Dr. Sudha Seshadri, corresponding study author, and professor of neurology at Boston University School of Medicine Alzheimer's Disease Center (BUSM) and Framingham Heart Study (FSH) senior investigator, in a statement.

Previous research suggests both too little sleep and too much sleep are linked to dementia. Missing out on deep non-REM (rapid eye movement) sleep may allow proteins linked to dementia to have easier access to the brain. Beta-amyloid, a protein suspected of triggering Alzheimer's, aggregates in higher concentrations in the brains of those who chronically suffer from poor sleep. As beta-amyloid accumulates, the protein further inhibits the ability to sleep, which feeds into a terrible cycle linked to dementia.

Researchers have also found education levels can affect the likelihood of developing dementia. Studies on dementia have consistently showed the more time spent in education, the lower the risk of developing the neurodegenerative disease. It seems people with more education are better able to compensate for the effects of dementia. Education in early life appears to help people cope with a lot of changes in their brain before showing dementia symptoms.

Now, Seshadri and her colleagues at Boston University School of Medicine Alzheimer's Disease Center provide further evidence longer sleep duration may be a marker of early neurodegeneration.

Close to 2,500 participants, with an average age of 72, self-reported total hours of sleep: six hours was categorized as short; six to nine hours was a reference point; and more than nine hours are categorized as long. They were asked about their sleep duration twice, 13 years apart, to determine how sleep duration affected dementia risk over time. During the years of follow-up, 234 cases of all-cause dementia were observed, and 181 cases were clinically consistent with Alzheimer's disease.

The findings revealed elderly people who consistently slept more than nine hours a night had double the dementia risk over a decade of follow-up. Excessive sleepers had smaller brain volumes and exhibited poor executive function. Moreover, participants without high school degrees who slept more than nine hours a night had six times the risk of developing dementia, compared to those who slept less than nine hours a night.

The researchers note there was not an increased risk in people who self-identified as excessive sleepers at both time points. However, those who were excessive sleepers on the second inquiry, but not the first, displayed a higher risk. These findings were driven by those who had mild cognitive impairment at the start of the study, and those without a high school degree.

"Collectively, these results suggest that long sleep duration serves as an early biological marker of neurodegeneration, especially in those with low educational attainment," wrote the researchers.

The researchers did note some study limitations, including unrecognized mild impairment at baseline, and analyzing sleep duration through self-reporting, which may not always be reliable. However, self-reported sleep duration is easy to obtain, which could potentially be a useful clinical tool to predict a person's dementia risk within 10 years. Doctors may be prompted to do further dementia screening for elderly patients who report excessive sleep and cognitive complaints.

Similar to previous hypotheses on the effects of sleep duration and dementia, Seshadri believes people may be sleeping longer as their body is reacting and trying to remove the buildup of amyloid in the brain.

This piece of dementia research may help doctors diagnose the neurodegenerative disease before it worsens.

The World Health Organization notes 47.5 million people have dementia and there are 7.7 million new cases every year. Alzheimer's disease, the most common type of dementia, may contribute 60 to 70 percent of cases.

In addition to prolonged sleep, there are two other surprising things linked to the onset of dementia that we should monitor carefully.

Loneliness

Spending too much time by yourself may trigger the onset of dementia. A 2013 study in the Journal of Neurology, Neurosurgery & Psychiatry found feelings of loneliness in older adults led to a 1.63 greater risk of developing dementia during the three years of the study. Although it's still unclear what drives this association, it seems like staying connected with loved ones can aid brain health.

Air Pollution

Living near a highway or a highly populated urban area can increase the likelihood of developing dementia for older women. A recent study in Translational Psychiatry found fine particulate matter, which consists of small particles that can be inhaled, triggers the odds of developing dementia by 92 percent, compared to women who lived in cleaner-air climates. Women who had the APOE4 gene, a genetic variant linked to risk for Alzheimer's disease, and were exposed to high levels of pollution, were more vulnerable to dementia.