Night Owl or Early Bird: Embrace or Alter Your Circadian Rhythm?

Growing up, I always heard the wisdom of “early to bed, early to rise,” attributed to Benjamin Franklin. However, life as a hospitalist doesn’t always follow that rule. Last week, I worked the night shifts when one of my colleagues was sick. While working night shifts, I became curious about how it affects our health. A study published in Annals of Internal Medicine caught my interest (1).

This prospective cohort study followed more than 60,000 middle-aged nurses aged 45 to 62 years from 2009 to 2017. The study found that individuals with an evening preference, meaning they feel more energetic later in the day (evening chronotype), had a higher risk for developing diabetes. Moreover, they were more prone to adopting unhealthy habits like smoking, inadequate sleep, and lack of physical activity than those with a morning preference (morning chronotype). Kianersi and colleagues (1) found that women with an evening chronotype were 54% more likely to have unhealthy lifestyle behaviors and had a 72% higher risk for diabetes than those with a morning chronotype (1, 2). The relationship between having an evening chronotype and the risk for diabetes was notably reduced after 6 lifestyle factors were accounted for. This emphasizes the impact of lifestyle behaviors on the connection between chronotype and diabetes.

Chronotype, or circadian preference, is a trait influenced by genetics, indicating a tendency toward earlier or later sleep times. Research has shown the connection between a late chronotype and a 30% increased risk for diabetes (2, 3). Circadian misalignment, arising from a discrepancy between an individual’s chronotype and work timing, could be a significant contributing factor. Adjusting work schedules by placing individuals with late chronotypes on night shifts and those with early chronotypes on morning shifts has proven effective in improving sleep among shift workers (4).

Interpreting this study’s findings requires careful consideration of several key factors. First, the simultaneous assessment of exposure and potential lifestyle “mediators” from the same questionnaire, coupled with the applied statistical methods, limits the ability to establish a clear causal pathway among chronotype, lifestyle factors, and diabetes. Even if chronotype and lifestyle were assessed sequentially, changes in chronotypes later might be correlated with subsequent lifestyle changes. In addition, compared with respondents to the chronotype question, nonrespondents were more likely to be non-White, have prevalent diabetes, and exhibit unhealthy lifestyle behaviors, potentially leading to an overestimation of the association between evening chronotype and diabetes risk. Furthermore, psychological factors associated with both evening chronotype and diabetes risk were not considered and could act as confounders. Another potential unmeasured confounder is the type of work, which may influence an individual’s chronotype, health behaviors, and diabetes risk.

To broaden the applicability of the findings, additional studies in different populations are required, especially focusing on genetic influences on chronotype. This will help determine if the results extend to men, non-White individuals, and diverse socioeconomic groups. It’s also important to account for generational variations in diet, exercise, and body weight to assess the relevance of the findings across age groups. At the end of the day, each of us has different priorities and preferences. Some days, a night owl may want to be an early bird, and vice versa. In health care, we need both to take care of our patients around the clock.

References

1. Kianersi S, Liu Y, Guasch-Ferré M, et al. Chronotype, unhealthy lifestyle, and diabetes risk in middle-aged U.S. women. A prospective cohort study. Ann Intern Med. 2023;176:1330-1339. [PMID: 37696036] doi:10.7326/M23-0728
2. Lin K, Song M, Giovannucci E. Evening chronotype, circadian misalignment, and metabolic health: implications for diabetes prevention and beyond. Ann Intern Med. 2023;176:1422-1423. [PMID: 37696034] doi:10.7326/M23-2257
3. Reutrakul S, Hood MM, Crowley SJ, et al. Chronotype is independently associated with glycemic control in type 2 diabetes. Diabetes Care. 2013;36:2523-9. [PMID: 23637357] doi:10.2337/dc12-2697
4. Vetter C, Fischer D, Matera JL, et al. Aligning work and circadian time in shift workers improves sleep and reduces circadian disruption. Curr Biol. 2015;25:907-11. [PMID: 25772446] doi:10.1016/j.cub.2015.01.064