Researchers used nationally representative data to examine the relationship between sleep disturbance and deficiency and their risk for incident dementia and all-cause mortality among older adults.
Are serious health consequences looming for those with trouble sleeping? Based on a large sum of available research, the answer appears to be yes—poor sleep poses an increased risk of dementia and all-cause mortality. But what defines poor sleep? Conflicting results have been reported by researchers regarding the characteristics of sleep when examining incident dementia and all-cause mortality. For instance, one meta-analysis suggests that sleeping fewer than five hours (short sleep) and longer than nine hours (long sleep) per night is associated with greater risk of mortality. Another meta-analysis finds that only longer than nine hours is associated with greater risk of mortality.
“Research on sleep disturbance and deficiency and all-cause mortality therefore has shown conflicting results. Further, few studies have included a comprehensive set of sleep characteristics in a single examination of incident dementia and all-cause mortality.”
From Brigham and Women’s Hospital, Harvard Medical School, and Boston College, based out of Massachusetts, United States, a team of researchers saw the need to address the gaps in this research and developed a new study. They organized a single examination of the relationships between a comprehensive set of sleep characteristics and incident dementia and all-cause mortality. This paper was entitled, “Examining sleep deficiency and disturbance and their risk for incident dementia and all-cause mortality in older adults across 5 years in the United States,” and published in Aging’s Volume 13, Issue 3 in February 2021.
The researchers collected baseline data from the National Health and Aging Trends Study (NHATS). The NHATS is a nationally-representative longitudinal study of Medicare beneficiaries (65 years and older) in the United States. The data were collected from a randomly selected subset of 2,812 participants from the NHATS population that were administered sleep questionnaires in 2013 and 2014.
“Participants with dementia at baseline (year 2013) were excluded (n = 202) for a sample of 2,812 with sleep data in either 2013 or 2014.”
The sleep characteristics measured from the questionnaire were: sleep duration, sleep latency, difficulty maintaining alertness, sleep quality, napping frequency, and snoring. First, participants rated their memory and performed a memory-related activity to assess their cognitive capacity and screen for incident dementia. Body weight was reported by participants annually, and diagnosis of heart attack, heart disease, hypertension, arthritis, diabetes, stroke, and cancer were also self-reported. Annual interviews were conducted to record instances of participant mortality. The researchers used Cox proportional hazards modeling and controlled for confounders to examine each sleep characteristic and outcome.
“Overall, our findings show a strong relationship between several sleep disturbance and deficiency variables and incident dementia over time.”
In the results adjusted for confounders, the team found that longer time to fall asleep and shorter sleep duration predicted incident dementia. They also found that short sleep duration, difficulty maintaining alertness, napping, and poor sleep quality predicted all-cause mortality. Given that short sleep duration was a strong predictor for both incident dementia and all-cause mortality, the researchers suggest that this may be the most important sleep characteristic related to adverse outcomes among older adults.
“The association observed in our study between short sleep (5 hours or less) and incident dementia screening may be understood via the research drawing upon animal models to demonstrate brain toxin removal during sleep .”
Another fascinating finding from this study was the difference between unadjusted and adjusted results for long sleep. As mentioned, previous studies have shown that long sleep is associated with both incident dementia and all-cause mortality. However, after the researchers adjusted for confounders, such as age and chronic conditions, the association between long sleep and incident dementia and all-cause mortality disappeared. The relationship between short sleep and both incident dementia and all-cause mortality remained significant even after full adjustment. These findings stand in contrast to the meta-analyses initially mentioned that have found associations between both short and long sleep and all-cause mortality in adults. The researchers suggest the cause may be that long sleep is a reflection of underlying disease.
“The most parsimonious explanation for the disappearance of the effect of long sleep on dementia and mortality in adjusted models is that the deleterious impact of long sleep is a reflection of underlying disease.”
The researchers confirm that addressing the sleep disturbance and deficiency variables in this study may have a positive impact on risk for incident dementia and all-cause mortality among older adults.
“Also, future research may consider the development of novel behavioral interventions to improve sleep among older adults.”
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