Being an “evening person” or a “night owl” increases the risk of diabetes by 19% compared with being an “early bird”, research has suggested.
Scientists found women who go to bed and wake up late – which means they have an “evening chronotype” – are also more likely to have unhealthy lifestyles.
Tianyi Huang, an associate epidemiologist at Brigham and Women’s Hospitals’ Channing Division of Network Medicine in the US, said: “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.
“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.”
The researchers analysed data from nearly 64,000 women from the Nurses’ Health Study II – which is among the largest investigations into the risk factors for major chronic diseases in women in the US – collected from 2009 to 2017.
It included self-reported sleeping habits, diet, weight and body mass index, sleep timing, smoking behaviour, alcohol use, physical activity and family history of diabetes.
The team also looked at medical records to see if the women had diabetes.
Of those taking part in the study, 11% reported having a definite evening chronotype and about 35% reported a definite morning chronotype.
The rest were labelled as intermediate, meaning they identified as neither a morning nor an evening person.
After accounting for lifestyle factors, evening chronotype was associated with a 19% increased risk of diabetes, the researchers said.
Among those with the healthiest lifestyles, only 6% had evening chronotypes, compared with 25% of night owls who reported having unhealthy lifestyles.
Evening people were also more likely to drink alcohol in higher quantities, have a low-quality food diet, get fewer hours of sleep per night, currently smoke, and have weight, BMI and physical activity rates in the unhealthy range, the team added.
Dr Sina Kianersi, a postdoctoral research fellow at the Channing Division of Network Medicine, said: “When we controlled for unhealthy lifestyle behaviours, the strong association between chronotype and diabetes risk was reduced but still remained, which means that lifestyle factors explain a notable proportion of this association.”
The association between evening chronotype and diabetes risk was stronger in nurses who worked day shifts as opposed to night shift workers, “suggesting that more personalised work scheduling could be beneficial”, according to the researchers.
The scientists are now planning to investigate the genetic causes of chronotype and its association with heart disease.
Dr Kianersi said: “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.”
The findings are published in the journal the Annals of Internal Medicine.