- The relationship between sleep and the risk of developing obesity or type 2 diabetes is not clear, but is thought to be bidirectional.
- Studies have shown that sleeping a different number of hours each night can be linked to diabetes risk.
- A new analysis of data from the UK Biobank shows that increased variability in sleep length is associated with a higher risk of diabetes, particularly in people who slept longer and in those with a lower genetic score for diabetes risk.
Irregular sleep was associated with the risk of type 2 diabetes, but this effect diminished when the data were adjusted for obesity, comorbidities and lifestyle factors.
Researchers from Boston (USA) and Manchester (UK) found that people with the greatest variability in sleep duration were 59% more likely to develop diabetes over a 7.5-year follow-up period than those whose sleep pattern was most stable.
The results were published in the journal Diabetes Care.
Risk increases with greater sleep irregularity
To investigate the link between irregular sleep and diabetes risk, the researchers used data from the UK Biobank, obtaining permission to use data from 84,421 participants for this study. The sleep data were available because participants were asked to wear an accelerometer – a device that records activity levels, much like a fitness watch – for seven days between 2013 and 2015.
The average age of the participants was 62, and the researchers also used genetic data stored in Biobank to calculate polygenic risk indicators for diabetes using known genetic variants of the condition.
The researchers found that participants whose sleep length deviation was between 31 and 45 minutes from the average had a 15% higher risk of diabetes compared to those whose sleep length varied by 30 minutes or less. Those with the highest variability, with a sleep length deviation of 91 minutes or more, had a 59% higher risk after adjusting for age, gender and race.
The researchers also analyzed differences in sleep duration above and below 60 minutes and found that a difference of more than 60 minutes was associated with a 34% increase in risk, but this decreased to 11% after adjusting the data for lifestyle factors, comorbidities, environmental factors and body fat levels.
The study group was 97% white and more than 45% had a university education, which is not representative of the UK population as a whole.
How sleep affects hormones
The authors did not explore the mechanisms underlying the discovered association in this prospective cohort study, but explained that it may be because irregular sleep patterns disrupt circadian rhythms. They suggested that an unstable circadian cycle may interfere with glucose metabolism and lead to reduced insulin sensitivity.
They studied the effect of sleep variability on diabetes risk, as there is growing evidence that sleep variability can affect metabolic health. Sleep length, sleep quality and other sleep disorders have previously been linked to diabetes risk in other studies.
Dr. Sudha Tallavajhula, a neurologist and sleep medicine specialist at UTHealth Houston who was not involved in the study, said in an interview with Medical News Today:
“For both clinical and research purposes, we see that sleep disturbances alter hormonal pathways. During sleep, the entire endocrine system, which includes all hormonal functions, cycles. Hormones that are not needed during sleep due to low activity, such as insulin and steroids, are usually reduced. Their levels rise in the morning to meet activity demands. Sleep disturbances contribute to improper glucose and fat utilization.”
It was not clear whether one causes the other, and the issue may have been a two-way street, she explained.
“There is a significant amount of research linking both obesity and diabetes to sleep disorders. From a broader perspective, sleep disorders are associated with the overall metabolic failure that underlies both diabetes and obesity. This relationship is multifactorial and works in both directions, meaning that sleep disorders can increase the risk of diabetes and obesity. These two conditions may also contribute to sleep disorders.”
– Dr. Sudha Tallavajhula
Circadian rhythm and the risk of type 2 diabetes
Previously, researchers investigated the role of circadian rhythm in the risk of type 2 diabetes. In a study published in the Annals of Internal Medicine, they examined Nurses’ Health Study II and found that “night brands” were more likely to develop type 2 diabetes than “morning birds.”
The chronotype, or whether people feel they need to go to bed and get up earlier or later, is linked to the circadian rhythm, which describes a person’s biological clock. It is believed to be controlled by light levels, among other factors.
The researchers also found that “night brands” were more likely to report unhealthy lifestyle behaviors. After adjusting the data for these factors, the chronotype effect was still present, but was attenuated.
Although the study did not explain the underlying mechanisms, it confirmed the importance of healthy habits in preventing type 2 diabetes, said Becca Anne Krukowski, professor of public health sciences at the University of Virginia, who was not involved in the study.
“Maintaining healthy habits – including regular sleep, but also regular physical activity and a healthy, balanced diet – contributes to overall health and probably to the prevention of type 2 diabetes,” – she said.
