People who tend to stay up late—referred to as night owls—are nearly 50% more likely to develop type 2 diabetes (T2D) compared to those who go to bed early. A new research presented at the European Association for the Study of Diabetes (EASD) 2024 annual meeting in Madrid highlights this strong link between sleep timing and the risk of developing T2D.
Lead researcher Dr. Jeroen van der Velde from Leiden University Medical Centre in the Netherlands states, “We’ve known for some time that night owls often have less healthy habits, but lifestyle factors alone don’t explain the increased risk of type 2 diabetes in late chronotypes.”
UNDERSTANDING CHRONOTYPES AND THEIR LINK TO DIABETES RISK
A person’s chronotype refers to their natural preference for sleep and wake times. In this study, researchers examined how different chronotypes—early, intermediate, and late—affect body composition and metabolic health. They focused on over 5,000 participants, as part of the Netherlands Epidemiology of Obesity study, which investigates how body fat influences health outcomes.
Participants were divided into three groups:
- Early chronotypes: The 20% of people with the earliest bedtimes.
- Late chronotypes: The 20% of people with the latest bedtimes.
- Intermediate chronotypes: The remaining 60%.
BMI, WAIST SIZE, AND FAT DISTRIBUTION IN LATE CHRONOTYPES
The study found that late chronotypes had higher body mass index (BMI), larger waist circumferences, and more visceral fat than early or intermediate chronotypes. On average, night owls had a BMI that was 0.7 kg/m² higher, a waist circumference 1.9 cm larger, and 7 cm² more visceral fat than their early-to-bed counterparts. These body fat distributions are particularly concerning as they are closely linked to metabolic disorders, including T2D.
Late sleepers also had 14% higher liver fat content, which is another risk factor for diabetes. These fat deposits around the organs can interfere with insulin sensitivity, making it more difficult for the body to regulate blood sugar levels.
CIRCADIAN RHYTHM MISALIGNMENT: MORE THAN JUST LIFESTYLE
While unhealthy habits like poor diet, lack of exercise, and smoking have long been associated with increased risk of T2D, this study suggests that something deeper is at play for night owls. The researchers adjusted the results to account for lifestyle factors, yet late chronotypes still had a significantly higher risk of developing T2D. This indicates that the misalignment between their internal body clock (circadian rhythm) and the traditional 9-to-5 societal schedule may be driving metabolic disturbances.
Dr. van der Velde explains, “Night owls may be in constant conflict with the external social and work environment. This circadian misalignment could lead to various metabolic issues, contributing to the increased diabetes risk.”
T2D RISK PERSISTS EVEN WHEN ADJUSTING FOR LIFESTYLE
To better understand the relationship between chronotype and T2D, the research team conducted a follow-up over a median period of 6.6 years. During this time, 225 participants were diagnosed with T2D. After adjusting for age, sex, education, total body fat, and a range of lifestyle factors—including physical activity, diet, alcohol intake, smoking, and sleep quality—the team found that late chronotypes had a 46% higher risk of T2D compared to intermediate chronotypes.
The findings suggest that even with healthy lifestyle changes, night owls are still at a disadvantage due to their circadian rhythm misalignment. This mismatch between biological clock and societal demands leads to disrupted sleep patterns, which can negatively affect hormone levels, including insulin.
ARE EARLY RISERS SAFER?
Interestingly, the study also looked at the risk of T2D among early chronotypes. Although previous research suggested early risers might have lower risks for metabolic diseases, the current study showed that early chronotypes had a slightly higher risk of T2D than intermediate chronotypes. However, this difference was not statistically significant, meaning there’s no strong evidence that going to bed too early provides any additional protection against diabetes.
HOW CAN NIGHT OWLS REDUCE THEIR RISK OF T2D?
For night owls concerned about their elevated risk of developing T2D, researchers are exploring ways to mitigate the effects of their late chronotype. One approach being studied is whether adjusting the timing of lifestyle habits—such as eating or exercising—could improve metabolic health. Dr. van der Velde and his team are currently part of the TIMED consortium, a research project aimed at understanding how the timing of sleep, food intake, and physical activity affects diabetes risk.
TIMING OF MEALS: A POTENTIAL INTERVENTION
One promising area of research involves the timing of meals. Late sleepers often eat later in the evening, a habit that could negatively affect metabolism. While the current study did not measure meal timing, previous research suggests that time-restricted eating (avoiding food after a certain time, like 6 p.m.) may lead to metabolic benefits. Night owls may benefit from adopting this eating pattern to reduce their diabetes risk.
“There is growing evidence that refraining from eating late in the evening can help improve metabolic health,” says Dr. van der Velde. “Night owls might want to consider trying time-restricted eating to see if it offers any benefits for their blood sugar control.”
FUTURE RESEARCH: UNDERSTANDING THE TIMING OF LIFESTYLE FACTORS
The TIMED consortium is focused on unravelling the complex relationships between the timing of various lifestyle factors and metabolic health. Early findings indicate that the timing of physical activity can influence insulin sensitivity. People who exercise earlier in the day may experience better blood sugar control than those who work out later in the evening.
Researchers are now looking at whether shifting other aspects of daily life, such as meal timing or even bedtime, could help reduce the risk of T2D in late chronotypes. “Our aim is to provide specific advice regarding the timing of lifestyle behaviours,” Dr. van der Velde explains.
