(Health): The Hidden Dangers of an Evening Chronotype - Night Owl Phenomenon

Large study of middle-aged nurses found those with an evening chronotype were more likely to engage in an overall unhealthy lifestyle particularly smoking, poor sleep, and physical inactivity, and had a 72 percent higher risk of developing diabetes.

Recent research involving over 60,000 middle-aged nurses has discovered that those with an evening chronotype, characterized by feeling more energetic later in the day, are at a heightened risk of diabetes. Additionally, these individuals tend to exhibit unhealthy lifestyle habits such as smoking, insufficient sleep, and physical inactivity.

This is when compared to individuals with a morning chronotype. However, the authors indicate that factors like profession, education level, and socioeconomic status of participants could influence these results. The study’s findings were released on September 12 in the Annals of Internal Medicine.

Understanding Chronotype

Chronotype, also known as circadian preference, is a partly genetically determined construct and refers to one’s inclination for earlier or later sleeping times. Roughly 8% of the population possesses an evening chronotype. Notably, this has been associated with poor metabolic regulation, disturbances in glycemic control, metabolic disorders, and a higher incidence and prevalence of type 2 diabetes. However, the precise reasons behind the observed connection between an evening chronotype and elevated diabetes risk remain elusive.

Detailed Study Findings

Scientists from Brigham and Women’s Hospital and Harvard Medical School conducted a prospective cohort study of 63,676 nurses aged 45 to 62 years with no history of cancer, cardiovascular disease, or diabetes from 2009 to 2017.

The researchers discovered that participants with a “definite evening” chronotype were 54 percent more likely to have an unhealthy lifestyle than participants reporting a “definite morning” chronotype. Persons with evening chronotype also had a 72 percent higher risk of developing diabetes during the follow-up period.

According to the authors, this association weakened but persisted even after adjusting for all measured lifestyle and sociodemographic factors. They emphasize that these results are restricted to persons who did not work recent night shifts. Future investigation in other populations leveraging genetic determinants for chronotype is needed to determine whether their findings are applicable to men, non-White racial or ethnic groups, or other socioeconomic classes. Furthermore, generational differences in diet, exercise, and body weight may limit the applicability of their findings to younger or older generations or current times.

A corresponding editorial by authors from the Harvard T.H. Chan School of Public Health and Harvard Medical School highlights that several factors, including psychological factors, type of work, and possible lifetime changes to chronotype could confound the results of this study. They add that the results suggest that circadian misalignment due to a mismatch between chronotype and work timing, rather than the chronotype, may be a potential mechanism for these results.

The editorial authors suggest that this study adds to the growing evidence that reassigning evening chronotype workers to night shifts may improve sleep among shift workers and improve their metabolic health. Finally, they note that these results point to the potential benefit of developing standardized tools to assess chronotype regularly throughout a person’s life.

Reference: “Chronotype, Unhealthy Lifestyle, and Diabetes Risk in Middle-Aged U.S. Women: A Prospective Cohort Study” by Sina Kianersi, DVM, PhD; Yue Liu, MD; Marta Guasch-Ferré, PhD; Susan Redline, MD, MPH; Eva Schernhammer, MD, DrPH; Qi Sun, MD, ScD and Tianyi Huang, ScD, MSc, 12 September 2023, Annals of Internal Medicine.

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