A new study has an important message for people who consider themselves night owls. Investigators from Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system, found that people with later sleep and wake times had less healthy lifestyles and were at greater risk of developing diabetes than those with early-bird sleep habits. Their results were published on September 12 in the Annals of Internal Medicine.
“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,” said corresponding author Tianyi Huang, MSc, ScD, an associate epidemiologist in the Brigham’s Channing Division of Network Medicine. “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 Study’s Findings
The researchers previously found that people with more irregular sleep schedules are at higher risk of developing diabetes and cardiovascular disease and that people with evening chronotypes are more likely to have irregular sleep patterns. For this study, they wanted to understand the relationship between chronotype and diabetes risk and looked at the role of lifestyle factors as well.
The team analyzed data from 63,676 female nurses from the Nurses’ Health Study II collected from 2009-2017 and included self-reported chronotype (the extent to which participants perceived themselves to be an evening person or a morning person), diet quality, weight and body mass index, sleep timing, smoking behaviors, alcohol use, physical activity, and family history of diabetes. The team determined diabetes status from the participants’ self-reports and medical records.
The Nurses’ Health Study II, a joint effort between the Brigham’s Channing Division of Network Medicine and 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 study’s strengths is its regular follow-up of study participants and repeated assessment of health and lifestyle factors.
Approximately 11 percent of participants reported having a ‘definite evening’ chronotype and about 35 percent reported having ‘definite morning’ chronotype. The remaining population, around half, were labeled as ‘intermediate,’ meaning they either identified as being neither a morning nor evening type or as being only slightly more one than the other.
The evening chronotype was associated with a 72 percent increased risk for diabetes before accounting for lifestyle factors. After accounting for lifestyle factors, evening chronotype was associated with a 19 percent increased risk of diabetes. Among those in the study with the healthiest lifestyles, only 6 percent had evening chronotypes. Among those with the unhealthiest lifestyles 25 percent were evening chronotypes.
Those with evening chronotypes were found to be more likely to drink alcohol in higher quantities, have a low-quality food diet, get less hours of sleep per night, currently smoke, and have weight, BMI, and physical activity rates in the unhealthy range.
Reference: “Chronotype, Unhealthy Lifestyle, and Diabetes Risk in Middle-Aged U.S. Women: A Prospective Cohort Study” by Sina Kianersi, DVM, PhD; Yue Liu, MD; Marta Guasch-Ferré, PhD; Susan Redline, MD, MPH; Eva Schernhammer, MD, DrPH; Qi Sun, MD, ScD and Tianyi Huang, ScD, MSc, 12 september 2023, Annals of Internal Medicine.
DOI: 10.7326/M23-0728
Funding: This study was funded by the National Institutes of Health (U01CA176726 and R01HL155395).
