‘Night owls' more likely to have unhealthy lifestyles, higher diabetes risk

In a retrospective cohort study, people with an evening chronotype were more likely to smoke, sleep poorly, and be physically inactive and had a 72% higher risk for diabetes than those with a morning chronotype.

People with an evening chronotype, defined as the circadian preference to feel energetic later in the day, were more likely to report unhealthy lifestyle behaviors such as smoking, poor sleep, and physical inactivity and were also at higher risk for diabetes, a study found.

Researchers used data from the Nurses' Health Study II to evaluate the role of modifiable lifestyle behaviors in the association between chronotype and diabetes risk. The study measured self-reported chronotype using a validated question from the Morningness-Eveningness Questionnaire, as well as diet quality, physical activity, alcohol intake, body mass index (BMI), smoking, and sleep duration. Participants self-reported incident diabetes cases, which were then confirmed via a supplementary questionnaire. The results were published Sept. 12 by Annals of Internal Medicine.

Overall, 63,676 nurses ages 45 to 62 years who had no history of cancer, cardiovascular disease, or diabetes from 2009 to 2017 were included in the study. Participants who reported having a “definite evening” chronotype were 54% (95% CI, 49% to 59%) more likely to have an unhealthy lifestyle than participants who reported having a “definite morning” chronotype. A total of 1,925 diabetes cases occurred over 469,120 person-years of follow-up. After adjustment for sociodemographic factors, shift work, and family history of diabetes, the adjusted hazard ratio (HR) for diabetes was 1.21 (95% CI, 1.09 to 1.35) for the “intermediate” chronotype and 1.72 (95% CI, 1.50 to 1.98) for the “definite evening” chronotype versus the “definite morning” chronotype.

After additional adjustment, the association comparing the “definite evening” versus the “definite morning” chronotypes was attenuated to 1.31 (95% CI, 1.13 to 1.50) for BMI, 1.54 (95% CI, 1.34 to 1.77) for physical activity, and 1.59 (95% CI, 1.38 to 1.83) for diet quality, respectively. When all measured lifestyle and sociodemographic factors were accounted for, a reduced but still positive association remained for the “definite evening” versus “definite morning” chronotype (HR, 1.19; 95% CI, 1.03 to 1.37).

The researchers emphasized that results involved only people who did not work recent night shifts and said that future studies of genetic determinants for chronotype are needed to determine whether these findings apply to men, non-White racial or ethnic groups, or other socioeconomic classes. “Moreover, generational differences in diet, exercise, and body weight may limit the applicability of findings to younger or older generations or current times,” they wrote.

An accompanying editorial highlighted that several variables, including psychological factors, type of work, and possible lifetime changes to chronotype, could confound the results and that circadian misalignment of chronotype and work shifts, rather than the chronotype alone, may also have an effect.

“Given that evening chronotype and circadian misalignment have been associated with increased risk for metabolic disorders and many other diseases, such as cardiovascular disease and depression, lifestyle interventions and personalized shift scheduling may have health benefits beyond diabetes prevention,” the editorial stated.