A large study of middle-aged nurses found that those with an evening chronotype were more likely to adopt unhealthy lifestyles overall, particularly smoking, sleep deprivation and lack of exercise, and had a 72% higher risk of developing diabetes. A recent study involving more than 60,000 middle-aged nurses found that people with an "evening chronotype" who feel more energetic later in the day were at a higher risk of developing diabetes.
Additionally, these individuals often exhibit unhealthy lifestyle habits such as smoking, sleep deprivation, and lack of exercise. This is compared to people with a morning type. However, the authors noted that factors such as participants' occupation, education level, and socioeconomic status may have affected these results. The findings were published in the Annals of Internal Medicine on September 12.
Understand circadian rhythm patterns
Circadian rhythm, also known as "circadian preference," is a partially genetically determined structure that refers to a person's tendency to sleep earlier or later. About 8% of people have a late bedtime chronotype. Notably, this is associated with poor metabolic regulation, disturbed glycemic control, metabolic disorders, and a higher incidence and prevalence of type 2 diabetes. However, the exact cause of the association between "evening type" and increased risk of diabetes remains elusive.
Detailed research results
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 between 2009 and 2017.
The researchers found that participants with a "definitely going to bed late" chronotype were 54% more likely to have an unhealthy lifestyle compared with participants with a "definitely waking up early" chronotype. People with a later bedtime schedule also had a 72% higher risk of developing diabetes during the follow-up period.
According to the authors, this association was attenuated but remained even after adjusting for all measured lifestyle and sociodemographic factors. They stressed that these results were limited to people who had not recently worked night shifts. Future investigations in other populations using genetically determined chronotypes are needed to determine whether their findings generalize to men, nonwhite racial or ethnic groups, or other socioeconomic classes. Additionally, generational differences in diet, exercise, and weight may limit the applicability of their findings to younger or older generations or to the current era.
editorial opinion
In a corresponding editorial, the authors from the Harvard T.H. Chan School of Public Health and Harvard Medical School stress that several factors, including psychological factors, job type, and possible lifetime changes in chronotype, may confound the study's results. They added that the findings suggest that circadian misalignment may be the underlying mechanism responsible for these results, due to a mismatch between chronotype and work hours, rather than chronotype.
The editorial authors believe this study adds to the growing body of evidence that moving late-shift workers to the night shift may improve sleep and improve metabolic health among shift workers. Finally, they note that these results suggest that there may be benefits in developing standardized tools to regularly assess a person's chronotype throughout their life.