Studies in mice have shown that during sleep the brain cleanses itself of neurotoxic substances and does so at twice the rate of clearance during waking hours. In a similar vein, a study of healthy young men found that a single night of total sleep deprivation increased blood levels of brain metabolites associated with neurodegenerative processes.
Based on these and related findings, researchers at Uppsala University in Sweden, led by Christian Benedict, associate professor (docent) of neuroscience in the Department of Neuroscience, decided to investigate whether self-reported sleep disturbances increase the risk of dementia in men.2
All 50-year-old men living in Uppsala County were invited to participate in the Uppsala Longitudinal Study of Adult Men. The study began with 1574 cognitively healthy men who were followed between 1970 and 2010. Dementia incidence was determined by reviewing each patient’s history between ages 50 and 90. At ages 60, 70, 77, 82, and 88, all subjects were invited to participate in follow-up investigations. At ages 50 and 70, they were asked to answer questions related to sleep habits, including, “Do you have difficulties falling asleep at night? Do you often wake up in the early hours, unable to get back to sleep?” and “Do you take sleeping pills more than 3 times per week?” If the participant had a positive answer to any of the 3 questions, he was presumed to have a sleep disturbance.
The results showed that men with self-reported sleep disturbances had a 1.3-fold higher risk of dementia and a 1.5-fold higher of Alzheimer disease than those without reports of sleep disturbances during a 40-year follow-up period. The older the age at which the self-reported sleep disturbance was indicated, the higher was the patient’s risk of Alzheimer disease.
According to lead author Benedict, the results show that “a regular good night’s sleep matters for your brain.”
The findings suggest that “strategies aimed at improving sleep quality (eg, regular exercise) may help reduce the neurodegenerative risk for a significant proportion of our society,” the authors state.
Benedict says the next steps are to investigate whether sleep-improving strategies (eg, sleep extension or establishing a sleep routine) help reduce the risk of Alzheimer disease in men.
“Studies utilizing methods that objectively measure sleep (eg, nocturnal polysomnography) will help to further our understanding as to why poor sleep patterns increase our risk [for] neurodegenerative diseases,” the authors state. “In this context, interventional studies with the intention of improving sleep patterns will be necessary to test whether such interventions can reduce the risk of developing neurodegenerative diseases and thus perhaps maintain cognitive health into older age.”
The researchers published their results online on October 27, 2014, in Alzheimer’s & Dementia.
Benedict C, Byberg L, Cedernaes J, et al. Self-reported sleep disturbance is associated with Alzheimer's disease risk in men. Alzheimer’s & Dementia. In press. http://www.alzheimersanddementia.com/article/S1552-5260%2814%2902819-2/pdf