For the last 30 years scientists have been telling us that not getting enough sleep may be a cause of type 2 diabetes.
Now a new study in the Journal of Clinical Endocrinology and Metabolism suggests that sleeping too much may also increase the risk of getting the disease.
Changing Sleep Patterns
According to its senior author, Femke Rutters of the VU Medical Centre in Amsterdam, the average self-reported sleep duration for individuals has fallen by 1.5 to 2 hours during the last 50 years, while diabetes rates have doubled in the same time frame.
That evidence is circumstantial, but Ms Rutters says in a statement: "In a group of nearly 800 healthy people, we observed sex-specific relationships between sleep duration and glucose metabolism.
"In men, sleeping too much or too little was related to less responsiveness of the cells in the body to insulin, reducing glucose uptake and thus increasing the risk of developing diabetes in the future. In women, no such association was observed."
To reach their conclusions the researchers studied 788 people enrolled in a European study looking at the link between insulin sensitivity and heart disease. The participants were healthy, aged between 30 and 60 and drawn from 14 European countries.
Sleep and physical activity was measured using a movement-tracker device and their risk of developing diabetes was assessed with a device that measured how effectively their body used the hormone insulin.
The study found that men who slept the least and the most were likely to have an impaired ability to process sugar when compared to men who slept for the average of 7 hours. Those who slept the most and the least had higher blood sugar levels than men who got the average amount of sleep.
However, women who slept less or more than average were more responsive to the hormone insulin than those who got 7 hours. The study found that they also had enhanced function of beta cells - the cells in the pancreas that produce the hormone insulin. It also suggests that lost sleep may not put women at increased risk of developing diabetes.
The researchers say a number of factors could be behind the differences between men and women. For instance, men are more frequently affected by sleep apnoea, which reduces sleep quantity and quality, while women have more slow-wave sleep which is known to be more 'restorative'.
Commenting on the findings in an emailed statement, Dr Elizabeth Robertson, director of research at Diabetes UK, says: "Many studies have now highlighted a potential link between abnormal sleep patterns and a higher risk of type 2 diabetes, but we have yet to establish why. This research suggests that it’s because too much or too little sleep affects the body's ability to respond to the levels of glucose in the blood, and the researchers found that this was specific to men.
"Due to the nature of the study, further work is needed to confirm these findings, and understand why the differences in sleep didn’t appear to affect women. Importantly, we know that the risk of type 2 diabetes can be reduced by maintaining a healthy weight, through taking regular exercise and eating a healthy balanced diet."
The Association Between Sleep Duration, Insulin Sensitivity, and B-Cell Function: The EGIR-RISC Study, F Rutters et al, Journal of Clinical Endocrinology and Metabolism
Press release, The Endocrine Society