Going to Bed Late May Increase Risk of Diabetes

A new study found that waking up late and going to bed late was associated with a 19 percent increased risk of diabetes for middle-aged women. Published in the journal Annals of Internal Medicine, the study indicates that those with an evening chronotype, more commonly known as "night owls," tend to have less healthy lifestyles than those with early-bird sleep habits, contributing to a greater risk of type 2 diabetes.

The investigation was conducted by a team of researchers at Brigham and Women’s Hospital in Boston. In their previous research, the team found that people with more irregular sleep schedules are at higher risk for developing diabetes and cardiovascular disease. For this study, they sought to better understand the relationship between peoples’ chronotypes, lifestyle habits, and risk of diabetes.

"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."

Researchers analyzed the data from 63,676 female nurses from 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, which is among the largest investigations into risk factors for major chronic diseases in women. The data was collected between 2009 and 2017 and included self-reported chronotype, diet quality, weight and body mass index, sleep timing, smoking behaviors, alcohol use, physical activity, and family history of diabetes. Researchers assessed the participants’ diabetes risk with self-reported data and medical records.

Among the participants, approximately 11 percent reported having a "definite evening" chronotype, and about 35 percent said they had a "definite morning" chronotype. The remaining participants fell between evening and morning chronotypes and were grouped into an “intermediate” category.

Before researchers accounted for lifestyle factors, the evening chronotype was associated with a 72 percent increased risk of diabetes. After lifestyle factors were accounted for, the evening chronotype was associated with a 19 percent increased risk of diabetes. Researchers also found that among the unhealthiest participants, 25 percent had evening chronotypes. In contrast, of the healthiest people, only six percent had evening chronotypes.

The study also showed that only nurses with evening chronotypes who worked day shifts, not overnight shifts, had an increased risk of diabetes.

"When chronotype was not matched with work hours, we saw an increase in type 2 diabetes risk," said Huang. "That was another very interesting finding suggesting that more personalized work scheduling could be beneficial."

While the study found a link between evening chronotype and an increased risk of diabetes, it did not determine causality. Researchers said they plan to further investigate evening chronotypes and their role in diabetes risk in larger, more diverse populations.

"If we are able to determine a causal link between chronotype and diabetes or other diseases, physicians could better tailor prevention strategies for their patients," said first author Sina Kianersi, DVM, PhD, a postdoctoral research fellow in the Brigham's Channing Division of Network Medicine.