Poor Sleep Quality is Linked to Alzheimer’s Disease and Higher All-Cause Mortality

“Get a good night’s sleep.” That’s a phrase we’re all familiar with, yet too many people do not heed this mood-altering and potentially life-saving advice. Consistent, undisrupted, quality sleep has important benefits for our overall health; however, the link between the quality of sleep, sleep disturbances, and health conditions in older age has been unclear. 

Now, new research out of the Harvard-affiliated Brigham and Women’s Hospital published in the journal Aging sheds some light on the important connection between sleep, risk of dementia, and overall mortality in old age. The Boston-based research team found that the risk of dementia was doubled among participants who reported getting less than five hours of sleep compared to those who reported 7 to 8 hours of sleep per night. The team also found links between sleep disturbance and deficiency with the overall risk of death.

The study’s senior author Dr. Stuart Quan says, "Our study demonstrates that very short sleep durations and poor-quality sleep in the elderly increase the risk of developing dementia and earlier death. There should be an increased focus on obtaining healthy sleep in older adults."

Sleep Quality’s Role in Future Health Risk

Sleep disturbance and deficiency are common among older adults, and there is some evidence linking poor sleep to risk for dementia and all-cause mortality. Research has found an association between sleep disturbances and abnormal sleep duration with the development and progression of Alzheimer’s disease (1).

It seems that the quality of sleep carries as much importance as the quantity of sleep. One study that examined over 700 healthy participants found that those with a high sleep fragmentation (interruptions of sleep) had a 1.5 fold risk of developing Alzheimer’s disease, compared to those with low sleep fragmentation (2).

Besides the association with cognitive impairment, sleep disturbances have also been linked to higher mortality rates for all causes (3). Other important risk factors that may predict cognitive decline in older age are: levels of daytime alertness (4), sleep latency (the amount of time it takes to fall asleep) (5), and sleep duration (6). Interestingly, both short and long sleep duration are associated with a greater risk of all-cause mortality (7). 

The good news regarding the sleep-dementia link is that recent studies suggest that older adults who reported signs of good sleep health (for example, waking up and feeling refreshed) have better cognitive function, an effect that leads scientists to believe that better sleep may serve as a buffer against the development of Alzheimer’s disease and dementia (8).

But, research on sleep disturbance or deficiency and all-cause mortality has shown conflicting results. And few studies have included a comprehensive set of sleep characteristics in a single examination of incident dementia and all-cause mortality. 

Study Sets Sights on Sleep’s Significance

The new research coming out of Boston addresses these gaps by examining the link between sleep disturbance, sleep duration, and alertness with incident dementia and all-cause mortality. . To find patterns that could link certain risk factors to health outcomes, the investigators at Brigham and Women’s Hospital analyzed data from the National Health and Aging Trends Study (NHATS), an observational study that follows Medicare beneficiaries who are at least 65 years old. The NHATS study is ongoing and has been collecting data from study participants since 2011.

Data regarding sleep patterns were collected from questionnaires that inquired about characteristics of sleep and deficiencies associated with lack of sleep, such as daytime alertness. The researchers also took into consideration data such as nap frequency, how long it took participants to fall asleep, quality of sleep, and snoring. To compare these data with future health outcomes like dementia and mortality risk, researchers collected data from participants’ health records up to five years after taking the sleep surveys.

The study found that dementia was associated with a very short sleep duration (5 hours or less) and with a lengthened sleep latency period (over 30 minutes to fall asleep). These two factors translated into a 45% increase in the risk of developing dementia.  Additionally, poor levels of daytime alertness were predictive of higher mortality.

Participants who reported that they routinely had to take naps, or had the worst levels of daytime alertness, had the greatest increase in all-cause mortality risk. Participants that reported poor sleep quality, or very short sleep duration (five hours or less) also had their risk increase substantially.

Commenting on the results from the study, senior study author Dr. Charles Czeisler said: "This prospective study reveals that sleep deficiency at baseline, when the average age of participants was 76 years old, was associated with double the risk of incident dementia and all-cause mortality over the next 4 to 5 years."

These results might be explained through the current understanding of the origins of Alzheimer’s, where it is hypothesized that proper sleep helps remove toxins and abnormal protein buildup in the brain. Recent research shows these proteins and toxins are produced at a higher rate during periods of wakefulness.

Even though previous studies have tried to explain the relationship between quality of sleep and all-cause mortality, findings were often contradictory. This study has taken into consideration several sleep characteristics that allow for visible patterns in the data. These findings highlight an association between early morning awakenings and worse cognitive function, but also an association between waking up feeling rested and better cognitive function over time.

Regarding the study, lead author Rebecca Robbins, Ph.D. said: "Our findings illuminate a connection between sleep deficiency and risk of dementia and confirm the importance of efforts to help older individuals obtain sufficient sleep each night. "

References:

1.     Irwin MR, Vitiello MV. Implications of sleep disturbance and inflammation for Alzheimer's disease dementia. Lancet Neurol. 2019;18(3):296-306. doi:10.1016/S1474-4422(18)30450-2
2. Lim AS, Kowgier M, Yu L, Buchman AS, Bennett DA. Sleep Fragmentation and the Risk of Incident Alzheimer's Disease and Cognitive Decline in Older Persons. Sleep. 2013;36(7):1027-1032. Published 2013 Jul 1. doi:10.5665/sleep.2802
3. Shen X, Wu Y, Zhang D. Nighttime sleep duration, 24-hour sleep duration and risk of all-cause mortality among adults: a meta-analysis of prospective cohort studies. Sci Rep. 2016;6:21480. Published 2016 Feb 22. doi:10.1038/srep21480
4. Shi L, Chen SJ, Ma MY, et al. Sleep disturbances increase the risk of dementia: A systematic review and meta-analysis. Sleep Med Rev. 2018;40:4-16. doi:10.1016/j.smrv.2017.06.010
5. Smagula SF, Jia Y, Chang CH, Cohen A, Ganguli M. Trajectories of daytime sleepiness and their associations with dementia incidence. J Sleep Res. 2020;29(6):e12952. doi:10.1111/jsr.12952
6. Diem SJ, Blackwell TL, Stone KL, et al. Measures of Sleep-Wake Patterns and Risk of Mild Cognitive Impairment or Dementia in Older Women. Am J Geriatr Psychiatry. 2016;24(3):248-258. doi:10.1016/j.jagp.2015.12.002
7. Bubu OM, Brannick M, Mortimer J, et al. Sleep, Cognitive impairment, and Alzheimer's disease: A Systematic Review and Meta-Analysis. Sleep. 2017;40(1):10.1093/sleep/zsw032. doi:10.1093/sleep/zsw032
8.     Robbins R, Sonnega A, Turner RW, et al. Sleep Difficulties and Cognition for 10 Years in a National Sample of U.S. Older Adults. Innov Aging. 2020;4(4):igaa025. Published 2020 Jun 29. doi:10.1093/geroni/igaa025