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Link established between more sleep, risk for dementia

Sleep duration could be a factor in determining a person’s risk for dementia, especially among patients with lower education levels, according to research recently published in Neurology.

"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,” Sudha Seshadri, MD, professor of neurology, Boston University School of Medicine, said in a press release. “These results suggest that being highly educated may protect against dementia in the presence of long sleep duration.”

Seshadri and colleagues examined self-reported hours of sleep among 2,457 participants in the previously conducted Framingham Heart Study. The mean age of the participants was 72 years, and 57% were women. Less than 6 hours of sleep was considered a short duration, 6 to 9 hours was considered the reference point, and more than 9 hours was considered a long duration. Researchers also stated that they looked for interactions with potential effect modifying variables such as age, sex, APOE ε4 allele status and education (no high school degree vs. at least a high school degree).

Researchers reported that 234 cases of all-cause dementia were observed over 10 years of follow-up and of these, 181 cases were clinically consistent with Alzheimer’s disease. In addition, prolonged sleep duration was associated with an increased risk for incident dementia (HR = 2.01; 95% CI, 1.24-3.26), with these findings propelled by persons with baseline mild cognitive impairment (HR = 2.83; 95% CI, 1.06-7.55) and persons without a high school degree (HR = 6.05; 95% CI, 3-12.18).

In addition, researchers also wrote that participants reporting sleeping more than 9 hours, as opposed to those who slept 6 to 9 hours, also showed poorer cross-sectional brain volume and lower cross-sectional processing speed and executive function.

“Associations between long sleep duration at baseline and dementia were driven by persons with [mild cognitive impairment] and persons without a high school degree. Whereas long sleep duration in the past was not associated with dementia risk, transitioning to more than 9 hours of sleep over a mean period of 13 years leading up to baseline was associated with an increased risk of dementia across the whole sample,” researchers wrote. “Collectively, these results suggest that long sleep duration serves as an early biological marker of neurodegeneration, especially in those with low educational attainment.”

Researchers stated that previous studies have indicated an association between long sleep duration and dementia, the temporal association between these events was in need of additional explanation.

“We extend previous findings by demonstrating that transitioning from sleeping 9 hours or less to more than 9 hours over a mean period of 13 years, was associated with a higher risk of incident dementia,” the researchers wrote. “In our study, long sleep duration in the past was not associated with an increased risk of dementia and sleep duration at baseline was only associated with the risks of dementia in those with [mild cognitive impairment]. Collectively, our findings suggest that transitioning to being a long sleeper is an early marker of neurodegeneration. Thus, interventions to reduce sleep duration in long sleepers are unlikely to mitigate clinical dementia risk.”

In light of this, researchers showed that an increase in sleep duration to more than 9 hours per night occurring over a mean period of 13 years before baseline was associated with an increased risk for all-cause dementia (HR = 2.43; 95% CI, 1.44-4.11) and clinical Alzheimer’s disease (HR = 2.2; 95% CI, 1.17–-4.13).

In addition, longer sleep duration was associated with a smaller total cerebral brain volume and worse executive function, as measured by the mean Trail Making Test B minus A score.

According to the press release, these results suggest that excessive sleep is not a cause of the brain changes that happen with dementia but is a symptom and thus, interventions to restrict sleep duration are unlikely to reduce the risk for dementia.

"Self-reported sleep duration may be a useful clinical tool to help predict persons at risk of progressing to clinical dementia within 10 years. Persons reporting long sleep time may warrant assessment and monitoring for problems with thinking and memory," Matthew P. Pase, PhD, department of neurology, Boston University School of Medicine, said in the press release.

The researchers noted their findings were in line with the anticipated results.

“The cross-sectional association between short sleep duration and poorer cognition was expected, given that performance on the Trail Making Test is dependent on cognitive processes, such as attention, which are impaired under conditions of sleep deprivation. Thus, the mechanisms linking short sleep duration to poorer cognitive function may be independent of any neurodegenerative disease,” they wrote. 

This study is one of the latest to explore possible connections between sleep and declines of brain function. A previously conducted meta-analysis suggested the quality of sleep between the ages of 30 and 60 was associated with cognitive decline, while another study suggested sleep disordered breathing sped up the onset of Alzheimer’s disease and dementia later in life. – by Janel Miller