Annals of Internal Medicine: Study finds people who sleep late have a 72% higher risk of diabetes

A large study of middle-aged nurses found that those with an evening chronotype were more likely to adopt an overall unhealthy lifestyle, especially smoking, insufficient sleep and lack of exercise, and had a 72% higher risk of diabetes. A recent study involving more than 60,000 middle-aged nurses found that people with "evening chronotypes" who feel more energetic later in the day are at a higher risk of diabetes.

In addition, these people tended to exhibit unhealthy lifestyle habits, such as smoking, insufficient sleep and lack of exercise. This was compared with morning people. However, the authors noted that factors such as the participants' occupation, education level and socioeconomic status may have influenced these results. The findings were published September 12 in the Annals of Internal Medicine.

Understanding circadian rhythm

Circadian typology, also known as "circadian preference," is a partially genetically determined construct that refers to a person's tendency toward earlier or later sleep times. Approximately 8% of the population has an evening sleep chronotype. Notably, this is associated with poor metabolic regulation, impaired blood sugar control, metabolic disorders, and a higher incidence and prevalence of type 2 diabetes. However, the exact cause of the link between "evening typology" and increased diabetes risk 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 "clearly late" chronotype were 54% more likely to have an unhealthy lifestyle compared to those with a "clearly early" chronotype. Those with a "clearly late" chronotype 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 emphasize that these results are limited to people who have not worked night shifts recently. Future investigations in other populations using genetically determined chronotypes are needed to determine whether their findings apply to men, non-white racial or ethnic groups, or other socioeconomic classes. In addition, generational differences in diet, exercise, and weight may limit the applicability of their findings to younger or older generations or to the present day.

Editorial Views

In an accompanying editorial, the authors from the Harvard T.H. Chan School of Public Health and Harvard Medical School emphasize that several factors, including psychological factors, type of work, and possible lifelong changes in chronotype, could confound the study's findings. They add that the findings suggest that circadian misalignment may be the underlying mechanism for these results, due to a mismatch between chronotype and work schedule, rather than chronotype.

The editorial authors suggest that this study adds to a growing body of evidence that moving evening chronotype workers to the night shift may improve sleep and metabolic health in shift workers. Finally, they note that these results suggest that there may be benefits to developing standardized tools to periodically assess chronotype throughout a person's life.