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Night owls have an increased risk of diabetes, new study finds

Night owls might want to rethink their habits. A recent investigation by researchers from Brigham and Women’s Hospital has uncovered a troubling connection between late sleep-wake cycles and an elevated risk of diabetes. 

The researchers explored the concept of “chronotype,” which refers to an individual’s innate circadian rhythm or preference for sleep and waking times. 

Circadian preference 

Study co-author Tianyi Huang is an associate epidemiologist at the Brigham’s Channing Division of Network 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 Huang.

“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.”

Focus of the study

Earlier studies by the team had identified a higher risk of diabetes and cardiovascular disease in individuals with inconsistent sleep patterns, with evening chronotypes often displaying irregular sleeping habits. This new research aimed to uncover the link between chronotype, lifestyle factors, and diabetes risk.

The exhaustive study scrutinized data from 63,676 female nurses as part of the Nurses’ Health Study II conducted between 2009 and 2017. 

Participants shared information about their perceived chronotype, dietary habits, weight, sleep timings, smoking and drinking habits, physical activity, and family history of diabetes. 

The study, a collaborative venture between the Brigham’s Channing Division of Network Medicine and Harvard T.H. Chan School of Public Health, is an expansive probe into the risk factors of major chronic diseases affecting women.

What the researchers learned 

A significant revelation was that 11% of participants identified strongly with an evening chronotype while 35% felt a definite morning inclination. The balance, about 50%, were more ambivalent, not particularly leaning towards either morning or evening.

Initially, evening chronotypes showed a 72% increased diabetes risk. However, upon considering lifestyle factors, this risk was revised to a 19% increase. 

Evening chronotypes 

Alarmingly, among the healthiest lifestyle group, just 6% were evening chronotypes, while 25% of those with less healthy habits identified with this category.

The night owls, the data suggests, were prone to consuming larger alcohol quantities, maintaining a poor diet, sleeping less, smoking, and exhibiting unhealthy weight and physical activity metrics.

Chronotype mismatch

“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,” said study first author Sina Kianersi, a postdoctoral research fellow in the Brigham’s Channing Division of Network Medicine.

The research also revealed a surprising trend: the heightened diabetes risk linked to the evening chronotype manifested primarily in nurses working daytime shifts, not those on overnight shifts.

“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.”

Study limitations 

However, a limitation of the study is its lack of diversity, focusing mainly on white female nurses. Further research across broader demographics is essential to ascertain the applicability of these findings universally. 

While the study highlights associations, it cannot firmly establish causality. Other factors might play a role in influencing a person’s chronotype, their susceptibility to unhealthy habits, and diabetes risk.

Future research

Looking ahead, the team plans to explore the genetic foundation of chronotype and its potential relationship with cardiovascular disease, alongside diabetes, in a broader, more diverse group of participants. 

“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,” says Kianersi.

The study is published in the journal Annals of Internal Medicine.

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