NEW research suggests that people with later sleep and wake times had less healthy lifestyles, and are at a greater risk of developing diabetes than those with ‘early-bird’ sleep habits. The research team, based at Channing Division of Network Medicine, Brigham and Women’s Hospital; and Harvard Medical School, both in Boston, Massachusetts, USA, commented: “Chronotype, or circadian preference, refers to a person’s preferred timing of sleep and waking, and is partly genetically determined, so it may be difficult to change.” They stressed: “People who think they are ‘night owls’ may need to pay more attention to their lifestyle, because their evening chronotype may add increased risk for Type 2 diabetes.”
The team analysed data from 63,676 female nurses included in the Nurses’ Health Study II, collected between 2009–2017. Self-reported chronotype, diet quality, BMI, smoking use, alcohol use, physical activity, weight, and sleep timing were among the measures analysed. The Nurse’s Health Study II is among the largest investigations into risk factors for major chronic diseases in females, with strengths including regular follow-up, and repeated assessments of health and lifestyle factors.
Approximately 11% of participants reported having a ‘definite evening’ chronotype, and approximately 35% reported having a ‘definite morning’ chronotype. The remaining population were labelled as ‘intermediate’, meaning they did not identify as being a morning or evening person. The evening chronotype was associated with a 72% increased risk for diabetes, before adjusting for lifestyle factors. This figure was reduced to 19% following this. Interestingly, among those with the healthiest lifestyles, only 6% had evening chronotypes, compared to 25% of those with the unhealthiest lifestyles having evening chronotypes. Specifically, those with evening chronotypes were found to be more likely to drink alcohol in higher quantities, have a low-quality food diet, sleep less, currently smoke, and have an unhealthy BMI.
The authors concluded: “When we controlled for unhealthy lifestyle behaviors, the strong association between chronotype and diabetes risk was reduced but still remained, which means that lifestyle factors explain a notable proportion of this association.” The authors acknowledge that the lack of diversity in the cohort, which mainly includes White female nurses, is a limitation. Future research will be required to determine whether the patterns detected here are consistent across populations.
