The authors did not look at the mechanisms underpinning the link they discovered in this prospective cohort study but explained it may be due to irregular sleep patterns disrupting circadian rhythms. They suggested this unstable circadian cycle could interfere with glucose metabolism and lead to reduced insulin sensitivity.

They looked at the effect of sleep variation on diabetes risk as there is increasing evidence sleep variation can have an impact on metabolic health. Sleep duration, sleep quality, and other sleep disturbances have been linked to diabetes risk in previous studies.

Sudha Tallavajhula, MD, neurologist, and sleep medicine physician at UTHealth Houston who was not involved in the research, told Medical News Today:

“In both clinical and research goals, we see that sleep disorders change hormonal pathways. During sleep, the whole endocrine axis, which is the pathway that encompasses all hormonal functions, undergoes a cyclical change. Hormones that are not required during sleep, because of low activity, for example, insulin and steroids are usually reduced. Their levels rise in the mornings, to meet demand for activity. Impaired sleep contributes to poor utilization of glucose and fat.”

It wasn’t clear if one caused the other and the issue could be bidirectional, she explained.

“There is a substantial amount of research that links both obesity and diabetes to sleep disorders. From a larger perspective, sleep disorders are linked to the overall metabolic inefficiency that underlies both diabetes and obesity. The relationship is multifactorial and goes both ways, meaning that sleep disorders can increase the risk of diabetes and obesity. These two conditions can also contribute to sleep disorders.”
— Sudha Tallavajhula, MD

Previously the researchers looked at the role of circadian rhythm on type 2 diabetes risk. For this study published in the Annals of Internal Medicine, they looked at the Nurses’ Health Study II, and discovered that ‘night owls’ were more likely to develop type 2 diabetes than ‘early birds’.

Chronotype, or whether people find they need to go to bed and wake up earlier or later, is linked to an individual’s circadian rhythm, which describes a person’s body clock. It is thought to be affected by light levels, among other things.

The researchers also found that ‘night owls’ were more likely to report unhealthy lifestyle behaviors. When data were adjusted for these factors, the effect of chronotype was still there but attenuated.

Although the study did not elucidate underlying mechanisms, it affirmed the importance of healthy routines for the prevention of type 2 diabetes, Becca Anne Krukowski P.h.D, professor of public health sciences at the University of Virginia School of Medicine, who was not involved in the research, told MNT.

“Maintaining healthy routines– including consistent sleep but also regular physical activity and healthy, balanced meals–contribute to overall health and likely prevention of type 2 diabetes,” she said.