The researchers found that nocturnal chronotype , or going to bed late and waking up late, was associated with a 19 percent increased risk of diabetes after accounting for lifestyle factors.
Background: Nighttime chronotype may promote adherence to an unhealthy lifestyle and increase the risk of type 2 diabetes. Aim: To evaluate the role of modifiable lifestyle behaviors in the association between chronotype and diabetes risk. Design: Prospective cohort study. Setting: Nurses’ health study II. Participants: A prospective follow-up was carried out until 2017 of 63,676 nurses between 45 and 62 years of age with no history of cancer, cardiovascular diseases or diabetes in 2009. Measurements: Self-reported chronotype using a validated question from the Morningness-Eveningness Questionnaire . The lifestyle behaviors measured were diet quality, physical activity, alcohol consumption, body mass index (BMI), smoking, and sleep duration. Incident cases of diabetes were self-reported and confirmed by a supplementary questionnaire. Results: Participants who reported a “definite evening” chronotype were 54% (95% CI, 49% to 59%) more likely to have an unhealthy lifestyle than participants who reported a “definite morning” chronotype. A total of 1,925 cases of diabetes were documented during 469,120 person-years of follow-up. Compared with the “definitive morning” chronotype, the adjusted hazard ratio (HR) for diabetes was 1.21 (CI, 1.09 to 1.35) for the “intermediate” chronotype and 1.72 (CI, 1 .50 to 1.98) for the “definitive nocturnal” chronotype after adjustment for sociodemographic factors, shift work, and family history of diabetes. Additional adjustment for BMI, physical activity, and diet quality attenuated the association when comparing “definite afternoon” and “definite morning” chronotypes with 1.31 (CI, 1.13 to 1.50), 1 .54 (CI, 1.34 to 1.77) and 1.59 (CI, 1.38 to 1.83), respectively. Limitations: Chronotype assessment using a single question, self-reported data, and homogeneity of the study population. Conclusion: Middle-aged nurses with a nighttime chronotype were more likely to report unhealthy lifestyle behaviors and had a higher risk of diabetes compared to those with a morning chronotype. Consideration of BMI, physical activity, diet, and other modifiable lifestyle factors attenuated much, but not all, of the increased risk of diabetes. Primary funding source: National Institutes of Health (NIH). |
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A new study has an important message for people who consider themselves night owls. Researchers at Brigham and Women’s Hospital, a founding member of the Mass General Brigham health care system, found that people with later sleep-wake times had less healthy lifestyles and were at higher risk of developing diabetes than those with early sleep. Their results are published in Annals of Internal Medicine .
"Chronotype, or circadian preference, refers to a person’s preferred sleep-wake schedule and is partly genetically determined, so it can be difficult to change," said corresponding author Tianyi Huang, MSc, ScD, associate epidemiologist at Brigham’s Channing Division. Online Medicine. "People who think they are ’night owls’ may need to pay more attention to their lifestyle because their nocturnal chronotype may increase the risk of type 2 diabetes."
Researchers previously found that people with more irregular sleep schedules have a higher risk of developing diabetes and cardiovascular disease and are more likely to have irregular sleep patterns. For this study, they wanted to understand the relationship between chronotype and diabetes risk and also looked at the role of lifestyle factors.
The team analyzed data from 63,676 nurses in the Nurses’ Health Study II collected between 2009 and 2017 and included self-reported chronotype (the degree to which participants perceived themselves as an evening or morning person), diet quality, weight and body mass index, sleep schedule, smoking, alcohol consumption, physical activity and family history of diabetes. The team determined diabetes status from participants’ self-reports and medical records.
The Nurses’ Health Study II, a joint effort between the Brigham’s Channing Division of Network Medicine and the Harvard T.H. Chan School of Public Health, is among the largest investigations into risk factors for major chronic diseases in women. One of the strengths of the study is the regular follow-up of participants and repeated evaluation of health and lifestyle factors.
About 11 percent of participants reported having a "definite evening" chronotype and about 35 percent reported having a "definite morning" chronotype. The remaining population, about half, was labeled "intermediate," meaning they did not identify as either morning or evening types or as slightly more one than the other.
Nighttime chronotype was associated with a 72 percent increased risk of diabetes before accounting for lifestyle factors. After accounting for lifestyle factors, nighttime chronotype was associated with a 19 percent increased risk of diabetes. Among study participants with healthier lifestyles, only 6 percent had nocturnal chronotypes. Among those with less healthy lifestyles, 25 percent were nocturnal chronotypes.
Those with nocturnal chronotypes were found to be more likely to drink alcohol in greater quantities, have a diet of low-quality foods, sleep fewer hours per night, currently smoke, and have weight, BMI, and physical activity indices in the unhealthy range.
"When we controlled for unhealthy lifestyle behaviors, the strong association between chronotype and diabetes risk was reduced but still maintained, meaning that lifestyle factors explain a notable proportion of this association," he said. first author Sina Kianersi, DVM, PhD, postdoctoral researcher. Brigham’s Channing Division of Network Medicine fellow.
They also found the association between nighttime chronotype and diabetes risk only in those nurses who worked day shifts and not in those who worked night shifts.
"When chronotype did not match working hours, we saw an increased risk of type 2 diabetes," Huang said. "That was another very interesting finding that suggests that more personalized work scheduling could be beneficial."
The Nurses’ Health Study is comprised primarily of white nurses; Future research will be needed to determine whether the patterns detected here are consistent across populations. The study results point to associations, but cannot determine causality: It is possible that other factors could contribute to a person’s chronotype, their propensity for unhealthy habits, and their risk of diabetes.
Next, the researchers plan to investigate the genetic determinants of chronotype and its association with cardiovascular disease, in addition to diabetes, in larger, more diverse populations.
"If we are able to determine a causal link between chronotype and diabetes or other diseases, doctors could better tailor prevention strategies for their patients," says Kianersi.
