Why night owls' 'mismatched' body clock could increase their risk of type 2 diabetes

Night owls have a higher risk of developing type 2 diabetes because their body clock is out of sync with society, experts have warned.

It is already known that those who stay up late and are more active at night are more likely to smoke, eat unhealthy food and have a higher body mass index, which are all linked to the condition.

However, the increased diabetes risk may not be down to lifestyle alone, researchers said.

Instead, they suggest the link could also be because a night owl's body clock may be out of sync with the rest of society.

A team from Leiden University Medical Centre in the Netherlands analysed sleep timing, waist circumference and the BMI of more than 5,000 people.

Of the group, 1,576 had MRI scans to measure visceral and liver fat, while electronic health records were used to check how many people had type 2 diabetes.

Patients were categorised into three groups, or 'chronotypes', based on their sleep timing - late, early and intermediate.

Dr Jeroen van der Velde, lead researcher, said: '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 at higher risk of obesity and metabolic disorders including type 2 diabetes.'

The group was followed up for an average of 6.6 years, during which 225 patients were diagnosed with type 2 diabetes.

When taking into account age, sex, total body fat and lifestyle factors such as exercise, diet and smoking, the study found people who preferred to stay up late still had a 46 per cent higher risk of type 2 diabetes than people in the intermediate group.

Dr van der Velde suggested there could be 'other mechanisms also at play' outside of lifestyle.

'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,' he said.

'This can lead to circadian misalignment, which we know can lead to metabolic disturbances and ultimately type 2 diabetes.'

Researchers also found night owls tended to have a higher BMI, a larger waist circumference, more visceral fat and higher liver fat content.

Dr van der Velde added: 'People with a late chronotype are probably more likely to eat until later in the evening.

'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 6pm, may lead to metabolic benefits.

'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 behaviour.'

The study will be presented at the annual meeting of the European Association for the Study of Diabetes in Madrid.