This large-scale Brazilian study is a pioneering report on the PAF of poor sleep quality using a multiracial cohort. Firstly, the PAF of poor sleep quality estimates the percentage of cases of dementia potentially preventable in Brazil, and potentially other LMICs given the representative potential of this country. Secondly, we estimated the prevalence of poor sleep quality, non-restorative sleep, and frequent use of sleep drugs extracted from this epidemiological sample. Lastly, our findings highlight the potential impact of targeting better sleep quality using a multiracial cohort in the prevention of dementia, which was not attributed to depressive symptoms.
The PAF provides important guidance for policymakers and stakeholders aimed to decrease the burden of dementia. A meta-analysis found that 15% of Alzheimer’s disease may be attributed to sleep problems in high-income countries 13, while we found that poor sleep quality alone had a PAF of 8%. This discrepancy between prevalences comes essentially from different definitions of sleep problems and consequently distinct estimated prevalences to calculate the PAF. Although heterogeneity in the assessment of outcomes and sleep problems may contribute to the overestimation of sleep complaints, the Brazilian or Latin American population was not represented in a previous meta-analysis 13. The high populational impact of poor sleep quality in dementia is consistent with the hypothesis that modifiable risk factors of cognitive decline play an important impact in LMIC. It may reflect poor healthcare assistance for cardiovascular diseases, lower educational levels, and sociodemographic vulnerabilities. Twelve potentially modifiable risk factors together have been associated with 40% of the PAF of dementia worldwide 15, while in Brazil this accounts for nearly half of cases of dementia 16. Importantly, the majority of individuals with dementia are living in LMIC, which is particularly uncovered by epidemiological data 17. Although there is a relative absence of specific evidence of the impact of risk factors on dementia risk in low and middle-income countries, particularly from Africa and Latin America 18, calculations considering the country-specific prevalence (not including Brazil) of nine potentially modifiable risk factors estimated overall PAF of 56% in Latin America 19,20. This whole scenario plays a massive role in mitigating the impact of dementia, especially in resource-limited countries.
A quarter of the sample reported poor sleep quality, while the prevalence of reported non-restorative sleep was around 50%. The prevalence of poor sleep quality, non-restorative sleep, and frequent use of sleep drugs were higher than described in other countries 21–23. Importantly, a cross-sectional analysis from National Health and Nutrition Survey including 4073 patients, mostly a healthy nonclinical sample, found that non-restorative sleep was reported in the majority of the study population, specifically 57.47% 24. Consistent with our findings, non-restorative sleep was associated with a myriad of characteristics shared with vulnerable populations in LMIC, such as black/African American ethnicity, lower educational levels, no private insurance, and very low environmental security 24. Sleep health is considered an important indicator of overall health, and it may reflect a self-perception of health 25, while high estimates of sleep problems may ultimately indicate worse health quality in this population. The high prevalence of subjective sleep disorders reported in this study highlight the potentially high impact of improving this modifiable risk factor of dementia in Brazil.26
Remarkably, disparities in sleep parameters were highly variable according to age range, race, and gender. Overall, black adult women and indigenous older women showed the highest rates of poor sleep quality, non-restorative sleep, and frequent use of sleep drugs. These subgroups also presented higher rates of symptoms of depression. According to racial identities, indigenous individuals presented a high frequency of poor sleep quality and non-restorative sleep when compared to other racial groups. A gender-specific analysis pointed out that women presented increased rates of poor sleep quality, non-restorative sleep, frequent use of sleep drugs, and symptoms of depression. Large population-based studies have also highlighted the higher prevalence of poor sleep quality in women 27. Besides, black and Hispanic individuals have been associated with worse sleep patterns when compared with Caucasian women 28–30. These findings are potentially associated with high social vulnerability and lack of emotional support 31. Sleep behavior and sleep disorders have a distinct pattern in women 32, which also have potential implications for the increased risk of dementia in this population. Potential reasons for the disparities aforementioned include genetic influence 33, complex socio-environmental factors, and structural racism 34,35. In primary care specifically, poor sleep quality may reflect the need for an individualized assessment, and it may arise as a target for clinical interventions 25.
Poor sleep quality was pointed out as an indicator of early cognitive impairment for elderly people in a Chinese cohort 36. Two meta-analyses found that sleep problems were associated with a higher risk of AD, cognitive impairment, and preclinical AD 13,37. Subjective sleep complaints were frequently associated with an increased risk of dementia 37, but studies on sleep quality are scarce. Poor sleep quality may reflect underlying pathological processes that arise from dysfunctions of circadian rhythms or disturbed sleep, and it presents an increased risk of overall cognitive impairment 38. Sleep deprivation, among other sleep-related factors, increases the accumulation of amyloid-beta proteins in the brain, in a potential bidirectional relationship 39. This study provides evidence that evaluating sleep quality through a single question, a proxy to a myriad of sleep problems may provide important information on the odds of cognitive decline. Strategies that include a brief evaluation of sleep quality in primary care may help identify those individuals at higher risk of dementia.
Strengths of our study include a complex large representative sample of the Brazilian elderly population and an extensive assessment of sociodemographic and health risk variables, enabling us to perform a comprehensive adjustment for potential confounders. Additionally, the sleep parameter used is very simple, making it easily translatable into daily clinical practice as a screening tool. Despite our efforts, this study also presented limitations. Sleep measurements were collected through self-report without including neuropsychological assessments, which can overestimate their real prevalence due to recall and social desirability bias 40. Also, assessment of sleep medication was limited to self-report of use, without further information about the type or dose of sleep medication, nor the indications for its prescription. Moreover, sleep quality was collected in both adults and older adults, which may present a risk or a consequence of neurodegenerative processes. As mentioned previously, sleep parameters may reflect an underdiagnosed depressive syndrome, with unclear cause or consequence in the context of dementia. Thus, further investigations may focus on biomarkers of poor sleep quality and measure objective sleep parameters accounting for depressive symptoms.
Finally, this study provides evidence for the high prevalence of poor sleep quality in a population representative of LMIC. Poor sleep quality is an important modifiable risk factor for dementia identified in this study. Poor sleep quality, non-restorative sleep, and frequent use of sleep drugs varied considerably between age ranges, sex, and gender. Our findings indicate that tailored public health strategies may greatly impact cognitive outcomes in the population. Further studies are warranted to examine the role of sleep management in benefiting cognition and preventing dementia.