Night owls have a higher BMI, larger waists, more hidden body fat and are roughly 50% more likely to develop type 2 diabetes (T2D) than earlier sleepers, according to a new study being presented at the European Association for the Study of Diabetes (EASD) Annual Meeting in Madrid, Spain (9-13 September).
Lead researcher Dr Jeroen van der Velde from Leiden University Medical Centre in Leiden, The Netherlands, said: “Previous studies have shown that a late chronotype (preferring to go to bed and wake up late) is associated with an unhealthy lifestyle. People with late chronotypes are more likely to smoke and have an unhealthy diet, for example, which has been suggested as why they are at higher risk of metabolic disorders, including obesity and type 2 diabetes.”
“However, we believe that lifestyle alone cannot fully explain the relationship between slow chronotype and metabolic disorders. Furthermore, although slow chronotype is known to be associated with higher BMI, it is not clear to what extent chronotype influences body fat distribution.”
To investigate further, van der Velde and his colleagues looked at the relationship between sleep duration, type 2 diabetes, and body fat distribution in more than 5,000 people as part of the Netherlands Obesity Epidemiology Study, an ongoing study into the impact of body fat on disease.
Participants included in the analysis were 54% female, with a mean age of 56 years and a mean BMI of 30 kg/m .2.
Participants filled in a questionnaire about their usual bedtime and wake-up times, from which a midpoint sleep score (MPS) was calculated.
Participants were then divided into three groups: early chronotypes (20% of participants with the earliest MPS), late chronotypes (20% of participants with the latest MPS), and intermediate chronotypes (60% of the remaining 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.
Participants were followed for an average of 6.6 years, during which time 225 were diagnosed with type 2 diabetes.
After adjusting for age, sex, education, body fat and various lifestyle factors (physical activity, diet quality, alcohol intake, smoking, and sleep quality and duration), participants with a later chronotype were shown to have a 46% higher risk of type 2 diabetes compared with those with an intermediate chronotype.
This suggests that the increased risk of type 2 diabetes in slow chronotypes cannot be explained by lifestyle alone.
“We believe there are other mechanisms at play as well. One possible explanation is that the circadian rhythms or internal clocks of slow chronotypes are out of sync with the work and social schedules that society follows. This leads to misalignment of circadian rhythms, which we know can lead to metabolic disorders and ultimately type 2 diabetes.”
Dr. Jeroen van der Velde, Leiden University Medical Center, Leiden, Netherlands
The team also investigated the risk of type 2 diabetes among early chronotypes.
“From the literature, we expected that the risk of developing type 2 diabetes for early chronotypes would be similar to that of intermediate chronotypes,” says Dr van der Velde. “Our results showed a slightly increased risk, but this was not statistically significant.”
The results also showed that slower chronotypes had a mean blood pressure of 0.7 kg/m2 High BMI, 1.9 cm Large waist circumference, 7 cm2 Compared to people with intermediate chronotypes, they had more visceral fat and 14% higher liver fat content.
Dr van der Velde concludes: “Late chronotypes appear to be at higher risk of developing type 2 diabetes compared to intermediate chronotypes, possibly due to higher levels of body fat, including visceral and liver fat.”
“The next step is to study whether lifestyle timing changes in slow chronotypes can improve metabolic health.
“We are currently part of the TIMED consortium, which is investigating the complex interactions between the timing of sleep, food intake and physical activity in relation to type 2 diabetes. We have previously shown that the timing of physical activity is important in relation to insulin resistance.”
Another example is changing the time you eat: “People with slower chronotypes probably tend to eat later in the evening,” says Dr van der Velde. “Although we didn't measure this in our study, there is growing evidence that time-restricted eating – not eating anything after a certain time, such as 6 p.m. – can have a positive effect on metabolism.”
“Night owls who are concerned about their increased risk of type 2 diabetes might want to try this, or at least cut down on late-night meals.
“We don't have the evidence yet, but our aim is to eventually provide specific advice on the timing of lifestyle actions.”“