More Evidence Ties Night Owls to Diabetes—But It’s Not Just Because of Lifestyle

Summary: Research presented at the European Association for the Study of Diabetes suggests that night owls, or those with a late chronotype, are at a significantly higher risk for developing type 2 diabetes, even after accounting for lifestyle factors like diet and exercise. The study, conducted on over 5,000 participants as part of the Netherlands Epidemiology of Obesity study, found that late chronotypes have a higher BMI, larger waistlines, and more hidden body fat, which contribute to the increased risk. Researchers believe that circadian misalignment, rather than just lifestyle, plays a critical role in this heightened risk.

Key Takeaways:

Night Owls Have a Higher Risk of Type 2 Diabetes: The study found that individuals with a late chronotype are 46% more likely to develop type 2 diabetes compared to those with an intermediate sleep schedule.
Body Fat Distribution Contributes to the Risk: Late chronotypes had higher BMI, larger waist circumference, and more visceral and liver fat, which are known risk factors for type 2 diabetes.
Circadian Misalignment May Play a Role: Researchers suggest that circadian misalignment, where the body’s internal clock is out of sync with societal schedules, could explain the increased diabetes risk among night owls beyond lifestyle factors.

Night owls have a higher BMI, larger waists, more hidden body fat, and are almost 50% more likely to develop type 2 diabetes than those who go to bed earlier, new research to be presented at the annual meeting of the European Association for the Study of Diabetes, has found.

“Previous studies have indicated that a late chronotype—preferring to go to bed late and wake up later—is associated with an unhealthy lifestyle. Late chronotypes are more likely to smoke or have an unhealthy diet, for example, and it has been suggested this is why they are higher risk of obesity and metabolic disorders including type 2 diabetes,” says lead researcher Jeroen van der Velde, PhD, Leiden University Medical Centre, in a release. “However, we believe that lifestyle cannot fully explain the relationship between a late chronotype and metabolic disorders. In addition, while it is known that a late chronotype is associated with high BMI, it isn’t clear to what extent chronotype affects body fat distribution.”

Study Explores Sleep Timing, Diabetes, and Body Fat Distribution

To find out more, van der Velde and colleagues studied the association between sleep timing, type 2 diabetes, and body fat distribution in more than 5,000 individuals, as part of the Netherlands Epidemiology of Obesity study, an ongoing study into the influence of body fat on disease.

The analysis involved participants (54% female) with a mean age of 56 years and mean BMI of 30 kg/m2. Participants filled in a questionnaire about their typical bed and waking times and from this midpoint of sleep (MPS) was calculated.

The participants were then divided into three groups: early chronotype (the 20% of participants with the earliest MPS), late chronotype (the 20% of participants with the latest MPS), and intermediate chronotype (the remaining 60% of participants).

BMI and waist circumference were measured in all participants. Visceral fat and liver fat were measured in 1,526 participants, using MRI scans and MR spectroscopy, respectively.

The participants were followed up for a median of 6.6 years, during which 225 were diagnosed with type 2 diabetes.

Higher Diabetes Risk in Late Chronotypes

The results, which were adjusted for age, sex, education, total body fat, and a range of lifestyle factors (physical activity, diet quality, alcohol intake, smoking, and sleep quality and duration), showed that compared with an intermediate chronotype, participants with a late chronotype had a 46% higher risk of type 2 diabetes.

This suggests that the increased risk of type 2 diabetes in late chronotypes can’t be explained by lifestyle alone.

Circadian Misalignment Could Be a Key Factor

“We believe that other mechanisms are also at play,” says van der Velde in a release. “A likely explanation is that the circadian rhythm or body clock in late chronotypes is out of sync with the work and social schedules followed by society. This can lead to circadian misalignment, which we know can lead to metabolic disturbances and ultimately type 2 diabetes.”

The team also looked at type 2 diabetes risk in early chronotypes.

“From the literature, we expected early chronotypes to have a similar risk of developing type 2 diabetes as intermediate chronotypes,” says van der Velde in a release. “Our results showed a slightly higher risk, but this was not statistically significant.”

Late Chronotypes Show Higher Body Fat Distribution

The results also showed that late chronotypes had a 0.7 kg/m2 higher BMI, 1.9 cm larger waist circumference, 7 cm2 more visceral fat, and 14% higher liver fat content, compared with those with an intermediate chronotype.

van der Velde concludes in a release, “People with a late chronotype appear to be at greater risk of developing type 2 diabetes compared to those with intermediate chronotype, possibly because of higher body fat including more visceral fat and liver fat. The next step is to study if those with a late chronotype improve in metabolic health when they make changes in the timing of their lifestyle habits.

Future Research to Focus on Timing of Lifestyle Habits

“We are currently involved in the TIMED consortium, where the complex interplay of the timing of sleep, food intake, and physical activity in relation to type 2 diabetes is examined. We previously showed that timing of physical activity is important in relation to insulin resistance.”

Another example would be to alter the timing of meals. “People with a late chronotype are probably more likely to eat until later in the evening,” says van der Velde in a release. “While we did not measure this in our study, there is growing evidence that time-restricted eating, not eating anything after a certain time, such as 6 pm, may lead to metabolic benefits.

He continues in a release, “Night owls who are concerned about the increased risk of type 2 diabetes might want to try this or, at least, try to refrain from eating late in the evening. The evidence isn’t there yet, but, in time, we aim to provide specific advice regarding the timing of lifestyle behavior.”