Sleep: Another benefit of regular sleep
A large observational study has found that irregular sleep-wake patterns are associated with a higher risk of overall mortality, and also mortality from cancers and cardiovascular disease.
- Channing Division of Network Medicine, Brigham and Women’s Hospital and Harvard Medical School, United States
- Division of Sleep Medicine, Harvard Medical School, United States
Benjamin Franklin’s famous quotation – “Early to bed and early to rise makes a man healthy, wealthy, and wise” – underscores the importance of sleep-wake patterns to our health and well-being. Of all the phenomena that are influenced by the 24 hour light-dark cycle, the sleep-wake cycle is the best known, but many other biological processes central to health are also influenced. However, empirical evidence about the impact that disruptions to sleep-wake patterns have on human health remains sparse and is mostly limited to studies on shift workers, despite an increase in other forms of disruption (notably higher levels of artificial light at night and increased use of mobile media in bed).
In recent years, an increasing number of studies have looked at the impact of sleep regularity (and irregularity) on aspects of health besides sleep quantity and quality, often made possible by the availability of wearable technology that is able to monitor rest-activity cycles in large numbers of people. Studies have found evidence that sleep irregularity is associated with a higher incidence of obesity (Patel et al., 2014), depression (Fang et al., 2021), cardiovascular disease (Huang et al., 2020) and other chronic disease outcomes.
Now, in eLife, Matthew Pase, Andree-Ann Baril and colleagues – including Lachlan Cribb, Ramon Sha and Stephanie Yiallourou, all of Monash University, as joint first authors – go one step further by linking sleep regularity with all-cause and cause-specific mortality in a large UK population (Cribb et al., 2023). Between 2013 and 2015, a total of more than 106,000 participants in the UK wore a watch-like device called an accelerometer over seven consecutive days. Based on the signals from this device it was possible to tell when the participants were asleep, sedentary, or active. Cribb et al. then derived a novel metric called the Sleep Regularity Index (SRI) to quantify day-to-day consistency in sleep-wake schedules. This metric is an estimate of how likely it is that a person is in the same state (that is, either awake or asleep) at any two time points 24 hours apart, with higher SRI values indicating higher sleep regularity. The researchers also noted how many of the participants subsequently died (via data from the UK national death register).
Over a median follow-up of 7.1 years, some 3,010 participants died, with 1,701 of these deaths being due to cancers and 616 being due to cardiovascular disease. Compared with those who had a medium SRI value, the top 5% (that is, the most regular sleepers) had 10% lower all-cause mortality, and the bottom 5% (that is, the most irregular sleepers) had 53% higher mortality. The association appeared nonlinear, with stronger associations observed for the increased mortality with more irregular sleep. Similar nonlinear patterns were observed when Cribb et al. examined cancer mortality and cardiovascular disease mortality separately.
The work by Cribb et al. is consistent with recent studies on sleep regularity and mortality from the US and Japan, although these findings are based on a smaller sample size (Chung et al., 2023a) or on self-reported sleep regularity (Omichi et al., 2022). Other studies found that sleep regularity was a stronger predictor for mortality than sleep duration or sleep apnea (Chung et al., 2023b; Windred et al., 2023). Interestingly, a genome-wide association study for sleep traits (Jones et al., 2019) reported a heritability estimate of 2.8% for sleep regularity, compared with 19.0% for sleep duration and 22.3% for fragmented sleep: this suggests that it may be easier to modify sleep regularity via interventions than it would be to modify other sleep traits because sleep regularity is less genetically determined.
Promoting sleep regularity is not a new idea in the area of ‘sleep hygiene’, and encouraging regular sleep schedules is also an essential component in cognitive behavioral therapy for insomnia (Sletten et al., 2023). From the behavioral perspective, promoting sleep regularity may also enhance the time-of-day effect of other behaviors, such as time-restricted eating and exercise. However, promoting sleep regularity for broader health promotion and disease prevention has not been tested in intervention studies and requires additional evidence from future investigations.
In summary, the study by Cribb et al. adds to the emerging evidence for the potential benefits of sleep regularity on chronic disease risk and mortality. The findings, in conjunction with prior evidence, provide a strong foundation to answer the following question: would public health interventions to improve sleep regularity causally lead to reductions in chronic disease and premature deaths at the population level?
References
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Sleep irregularity and risk of cardiovascular events: The Multi-Ethnic Study of AtherosclerosisJournal of the American College of Cardiology 75:991–999.https://doi.org/10.1016/j.jacc.2019.12.054
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The association between sleep patterns and obesity in older adultsInternational Journal of Obesity 38:1159–1164.https://doi.org/10.1038/ijo.2014.13
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- Version of Record published: December 1, 2023 (version 1)
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© 2023, Huang
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Sleep: Another benefit of regular sleep
eLife 12:e94131.
https://doi.org/10.7554/eLife.94131
Further reading
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- Epidemiology and Global Health
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Background: Few national-level studies have evaluated the impact of 'hybrid' immunity (vaccination coupled with recovery from infection) from the Omicron variants of SARS-CoV-2.
Methods: From May 2020 to December 2022, we conducted serial assessments (each of ~4000-9000 adults) examining SARS-CoV-2 antibodies within a mostly representative Canadian cohort drawn from a national online polling platform. Adults, most of whom were vaccinated, reported viral test-confirmed infections and mailed self-collected dried blood spots to a central lab. Samples underwent highly sensitive and specific antibody assays to spike and nucleocapsid protein antigens, the latter triggered only by infection. We estimated cumulative SARS-CoV-2 incidence prior to the Omicron period and during the BA.1/1.1 and BA.2/5 waves. We assessed changes in antibody levels and in age-specific active immunity levels.
Results: Spike levels were higher in infected than in uninfected adults, regardless of vaccination doses. Among adults vaccinated at least thrice and infected more than six months earlier, spike levels fell notably and continuously for the nine months post-vaccination. By contrast, among adults infected within six months, spike levels declined gradually. Declines were similar by sex, age group, and ethnicity. Recent vaccination attenuated declines in spike levels from older infections. In a convenience sample, spike antibody and cellular responses were correlated. Near the end of 2022, about 35% of adults above age 60 had their last vaccine dose more than six months ago, and about 25% remained uninfected. The cumulative incidence of SARS-CoV-2 infection rose from 13% (95% CI 11-14%) before omicron to 78% (76-80%) by December 2022, equating to 25 million infected adults cumulatively. However, the COVID-19 weekly death rate during the BA.2/5 waves was less than half of that during the BA.1/1.1 wave, implying a protective role for hybrid immunity.
Conclusions: Strategies to maintain population-level hybrid immunity require up-to-date vaccination coverage, including among those recovering from infection. Population-based, self-collected dried blood spots are a practicable biological surveillance platform.
Funding: Funding was provided by the COVID-19 Immunity Task Force, Canadian Institutes of Health Research, Pfizer Global Medical Grants, and St. Michael's Hospital Foundation. PJ and ACG are funded by the Canada Research Chairs Program.
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The chemical composition of foods is complex, variable, and dependent on many factors. This has a major impact on nutrition research as it foundationally affects our ability to adequately assess the actual intake of nutrients and other compounds. In spite of this, accurate data on nutrient intake are key for investigating the associations and causal relationships between intake, health, and disease risk at the service of developing evidence-based dietary guidance that enables improvements in population health. Here, we exemplify the importance of this challenge by investigating the impact of food content variability on nutrition research using three bioactives as model: flavan-3-ols, (–)-epicatechin, and nitrate. Our results show that common approaches aimed at addressing the high compositional variability of even the same foods impede the accurate assessment of nutrient intake generally. This suggests that the results of many nutrition studies using food composition data are potentially unreliable and carry greater limitations than commonly appreciated, consequently resulting in dietary recommendations with significant limitations and unreliable impact on public health. Thus, current challenges related to nutrient intake assessments need to be addressed and mitigated by the development of improved dietary assessment methods involving the use of nutritional biomarkers.
