Sleep and cognitive performance of African-Americans and European-Americans before and during circadian misalignment produced by an abrupt 9-h delay in the sleep/wake schedule

Understanding the determinants of circadian health disparities and cardiovascular disease

Emerging research suggests that sleep contributes to racial disparities in cardiovascular disease (CVD). Racial/ethnic minorities are disproportionately affected by poor cardiovascular outcomes including obesity, hypertension and diabetes. Although circadian rhythms affect sleep patterns, few studies have examined disparities in circadian health or the contribution of circadian disparities to CVD. In this paper, we provide an overview of the relation between circadian health and CVD in the context of health disparities. We discuss (1) the current knowledge on racial disparities in circadian health; (2) social and environmental determinants of circadian health disparities; (3) the cardiovascular consequences of circadian disparities; and (4) future opportunities to advance the field of circadian disparities. In brief, our findings demonstrated that among a small literature, racial minorities (mainly African American) were more likely to have a shorter circadian period, delayed phase shifts, and were more likely to be shift workers, which are associated with CVD risk factors. Given racial minorities are disproportionately affected by CVD and CVD risk factors, it is important to further understand circadian health as an intervention target and support more research among racial minorities to understand circadian health in these populations.

Differences in sleep timing and related effects between African Americans and non-Hispanic Whites

STUDY OBJECTIVES

Prior studies have shown a morning chronotype for African Americans compared with non-Hispanic Whites, yet self-reported sleep timing is delayed in African Americans compared with Whites.

METHODS

We analyzed data from the Multi-Ethnicity Study of Atherosclerosis, a multisite community-based cohort. Self-reported and actigraphic sleep timing, chronotype measured by the modified Horne-Östberg Morningness-Eveningness Questionnaire, and risk of depression measured by the Center for Epidemiologic Studies Depression scale were examined using nonparametric approaches and linear or logistic regression while comparing between African Americans and Whites and evaluating the effects of delayed sleep phase.

RESULTS

In 1,401 participants, there was no difference in chronotype between African Americans and Whites. African Americans were 80% more likely to report a delayed sleep phase (defined as bedtime after midnight) on weekdays and 50% more likely on weekends than were Whites. Actigraphic data showed similar results. Actigraphic midsleep time was delayed 38 minutes on weekdays and 24 minutes on weekends in African Americans compared with Whites. Stratified analysis by chronotype showed that African Americans with a morning or intermediate chronotype had a significantly delayed sleep phase compared with Whites, but there was no difference between African Americans and Whites with an evening chronotype. Delayed sleep phase was associated with depression, but this relationship was only significant in White participants.

CONCLUSIONS

African Americans had a delayed sleep phase compared with Whites that was more pronounced in individuals with a morning or intermediate chronotype. Consequences of delayed sleep phase may vary by race and ethnicity.

Circadian Effects of Drug Responses

Circadian rhythms describe physiological systems that repeat themselves with a cycle of approximately 24 h. Our understanding of the cellular and molecular origins of these oscillations has improved dramatically, allowing us to appreciate the significant role these oscillations play in maintaining physiological homeostasis. Circadian rhythms allow living organisms to predict and efficiently respond to a dynamically changing environment, set by repetitive day/night cycles. Since circadian rhythms underlie almost every aspect of human physiology, it is unsurprising that they also influence the response of a living organism to disease, stress, and therapeutics. Therefore, not only do the mechanisms that maintain health and disrupt homeostasis depend on our internal circadian clock, but also the way drugs are perceived and function depends on these physiological rhythms. We present a holistic view of the therapeutic process, discussing components such as disease state, pharmacokinetics, and pharmacodynamics, as well as adverse reactions that are critically affected by circadian rhythms. We outline challenges and opportunities in moving toward personalized medicine approaches that explore and capitalize on circadian rhythms for the benefit of the patient.

Delayed Sleep Time in African Americans and Depression in a Community-Based Population

STUDY OBJECTIVES

Studies have shown racial differences in circadian rhythm in African Americans when compared to non-Hispanic whites, and an association between circadian dyssynchrony and depression. We hypothesized that the prevalence of delayed sleep time is greater in African Americans when compared to whites and that delayed sleep time is associated with depression.

METHODS

We analyzed data from the Sleep Heart Health Study (SHHS), a large community-based sample. Delayed sleep time was defined as self-reported weeknight bedtime after midnight. Depression was defined based on participant's response to the question, "In the past 4 weeks have you felt downhearted and blue?" or reported antidepressant use. We performed multivariate linear and logistic regression, adjusting for age, sex, race, body mass index, smoking, apnea-hypopnea index, alcohol use, and caffeine consumption.

RESULTS

Adjusted weekday bedtime was 15 ± 7 minutes later in African Americans compared to whites (P < .001). Similarly, weekend bedtime was 18 ± 7 minutes later in African Americans compared to whites (P = .025). The prevalence of delayed sleep time was greater in African Americans (33.3%) compared to whites (18.7%; P < .001). After adjusting for confounders, when compared to whites, a greater proportion of African Americans had delayed sleep time (adjusted odds ratio [aOR] 2.03; 95% confidence interval [95% CI] 1.5, 2.4; P < .0001). Depression was independently associated with delayed sleep time after adjustment (aOR 1.4; 95% CI 1.1, 1.7; P = .007).

CONCLUSIONS

African Americans are more likely to have a delayed sleep time compared to whites, and delayed sleep time was independently associated with depression.

The Effects of Moderate Physical Exercise on Adult Cognition: A Systematic Review

Background: Physical exercise is a systematic sequence of movements executed with a predefined purpose. This muscular activity impacts not only on circulatory adaptations, but also neuronal integration with the potential to influence cognition. The aim of this review was to determine whether the literature supports the idea that physical exercise promotes cognitive benefits in healthy adults.

Methods: A systematic search for relevant articles was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analysis criteria using available databases (PubMed, LILACS, Scopus, Web of Science, The Cochrane Library, OpenGrey, Google Scholar and CENTRAL). The search terms included “humans” or “adults” or “cognition” or “awareness” or “cognitive dissonance” or “cognitive reserve” or “comprehension” or “consciousness” and “motor activity” or “exercise” or “physical fitness,” and not “aged” or “nervous system diseases,” with the purpose of finding associations between moderate physical exercise and cognition. A methodological quality and risk of bias unit assessed the eligibility of articles.

Results: A total of 7179 articles were identified. Following review and quality assessment, three articles were identified to fulfill the inclusion criteria. An association between moderate physical exercise and cognition was observed. Improvements in cognitive parameters such as reduced simple reaction time, improved response precision and working memory were identified among the included articles.

Conclusion: This systematic review found that moderate physical exercise improves cognition.