Young female at laptop computer eats instant ramen noodles late in the evening. Woman working or studying online overtime at night has fast dinner – concept of unhealthy junk food at workplace

(© Photoboyko -

BOSTON — For those who love to stay up late or have no choice because of their work schedule, researchers warn that those nighttime patterns could lead to long-term health problems. Night owls face a 19-percent higher risk of developing diabetes compared to early birds, a new study explains.

“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,” says Dr. Tianyi Huang, the corresponding author and an associate epidemiologist at Brigham and Women’s Hospital. “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.”

Previous research by the team discovered that individuals with irregular sleep schedules had an increased risk of both diabetes and heart disease. They also noted that those with evening chronotypes tended to have more irregular sleep patterns. With this new study, the researchers aimed to explore the connection between chronotype and diabetes risk, factoring in lifestyle habits.

The study analyzed data from over 63,000 female nurses, taking into account self-reported chronotype, diet quality, weight, body mass index (BMI), sleep timing, as well as drinking and smoking habits. Roughly one in nine participants identified as having a “definite evening” chronotype, whereas about 35 percent reported a “definite morning” chronotype. The remaining participants were categorized as “intermediate,” meaning they neither distinctly identified as morning people or night owls or showed only a slight preference for one over the other.

woman sleeping under weighted blanket
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.
(© Katelin –

Prior to adjusting for lifestyle factors, having an evening chronotype was associated with a 72-percent increased risk of diabetes. After the adjustment, the risk remained elevated at 19 percent, according to the study report.  Only six percent of those with the healthiest lifestyles were evening chronotypes, compared to 25 percent among those with the least healthy lifestyles.

“Even after controlling for unhealthy lifestyle behaviors, the strong association between evening chronotype and diabetes risk persisted, albeit reduced. This suggests that lifestyle factors account for a significant portion of this association,” adds Dr. Sina Kianersi, the first author of the study, in a media release.

Interestingly, the research team discovered that the increased risk linked to evening chronotype was evident only in nurses working day shifts, not in those working overnight.

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

The researchers now aim to explore the genetic determinants of chronotype and its potential association with not just diabetes but also heart disease.

“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,” concludes Dr. Kianersi.

The findings are published in the journal Annals of Internal Medicine.

South West News Service writer Stephen Beech contributed to this report.

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