sleep Archives | Misha Blagosklonny

In a new study, researchers investigated the association between sleep, cognitive reserve and cognition in older adults.

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Sleep is vital for our health and well-being, but as we age, we tend to experience less and less of it. In particular, we lose some of the deep sleep stages, known as slow wave sleep (SWS), that are crucial for memory consolidation and brain maintenance. This can affect cognitive performance and increase our risk of developing dementia.

Not everyone is equally vulnerable to the negative effects of poor sleep quality. Some people seem to be more resilient and able to cope with less SWS without compromising their mental abilities. What makes them different? One possible factor is cognitive reserve (CR).

CR is a concept that refers to the brain’s ability to adapt and compensate for age-related changes or brain damage. It is influenced by various aspects of our life experiences, such as education, occupation, leisure activities, social interactions, and mental stimulation. People with higher CR are thought to have more efficient brain networks, more cognitive strategies, and more brain reserve (i.e., more neurons and connections) that can buffer the impact of aging or pathology on cognition.

In a new study, researchers Valentin Ourry, Stéphane Rehel, Claire André, Alison Mary, Léo Paly, Marion Delarue, Florence Requier, Anne Hendy, Fabienne Collette, Natalie L. Marchant, Francesca Felisatti, Cassandre Palix, Denis Vivien, Vincent de la Sayette, Gaël Chételat, Julie Gonneaud, and Géraldine Rauchs from Normandie University, UNI – ULB Neuroscience Institute, University of Liege, University College London, and CHU de Caen aimed to identify individuals in whom sleep disturbances might have greater behavioral consequences. On September 28, 2023, their research paper was published in Aging’s Volume 15, Issue 18, entitled, “Effect of cognitive reserve on the association between slow wave sleep and cognition in community-dwelling older adults.”

The Study

The researchers investigated whether CR could modulate the association between SWS and cognition in older adults. The researchers recruited 135 cognitively intact older adults (mean age: 69.4 years) from the Age-Well randomized controlled trial and measured their sleep quality using polysomnography — a technique that records brain waves, eye movements, muscle activity, and other physiological signals during sleep. They also assessed their cognitive performance using neuropsychological tests that evaluated executive function (i.e., the ability to plan, organize, monitor, and control one’s behavior) and episodic memory (i.e., the ability to remember personal events and experiences).

To estimate CR, the researchers used two measures of cognitive engagement throughout life: a questionnaire that asked about the frequency and diversity of participation in various activities (such as reading, playing games, learning languages, etc.) in different age periods; and a composite score based on the highest level of education attained, the complexity of the main occupation held, and the current cognitive activity level.

The results showed that SWS was positively associated with episodic memory performance, meaning that participants who had more SWS tended to have better memory scores. However, this association was not observed for executive function performance. CR proxies modulated the associations between SWS and both executive and episodic memory performance. Specifically, participants with higher CR were able to maintain cognitive performance despite low amounts of SWS, whereas participants with lower CR showed a steeper decline in performance as SWS decreased.

“This study provides the first evidence that CR may protect against the deleterious effects of age-related sleep changes on cognition.”

Conclusions

The study suggests that engaging in cognitively stimulating activities throughout life may enhance one’s ability to cope with less SWS without compromising one’s mental abilities. It also highlights the importance of considering individual differences in CR when evaluating the impact of sleep quality on cognition in older adults.

The authors were forthcoming about limitations of their study, such as the cross-sectional design that does not allow causal inferences, the relatively small sample size that limits the generalizability of the findings, and the use of proxy measures that may not capture all aspects of CR. They also point out some directions for future research, such as exploring the underlying mechanisms of how CR influences sleep-cognition relationships, examining whether CR can also modulate the effects of other sleep parameters (such as sleep duration or fragmentation) on cognition, and investigating whether interventions that target sleep quality or CR can improve cognitive outcomes in older adults.

In conclusion, this study suggests that CR may be an important factor that can help us sleep better and think sharper as we age. It also encourages us to keep our brains active and challenged throughout our lives, as this may benefit not only our cognitive functioning but also our sleep quality.

“These findings are important to understand the factors promoting successful aging and suggest that the deleterious impact of sleep disturbances could be counteracted by an enriched lifestyle. This will help to design non-pharmacological interventions to promote successful aging and counter age-related sleep changes.”

Click here to read the full study published in Aging.

Interested in reading more about cognitive reserve and aging? Click here.

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Aging is an open-access, traditional, peer-reviewed journal that has published high-impact papers in all fields of aging research since 2009. All papers are available to readers (at no cost and free of subscription barriers) in bi-monthly issues at Aging-US.com.

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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.

Person sleeping in bed and alarm clock in the foreground

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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 Study

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.

Results

“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 [24].”

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.”

Conclusion

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.”

Click here to read the full study, published on Aging-US.com.

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Aging is an online open-access journal that publishes research papers monthly in all fields of aging research and other topics. These papers are available to read at no cost to readers on Aging-us.com. Open-access journals offer information that has the potential to benefit our societies from the inside out and may be shared with friends, neighbors, colleagues, and other researchers, far and wide.

For media inquiries, please contact [email protected].

Tag: sleep

Risks for Dementia and Mortality: Sleep Disturbance and Deficiency

The Study

Results

Conclusion

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