Chronic insufficient sleep can increase insulin resistance in otherwise healthy women, with more marked effects in postmenopausal women, according to a study funded by the National Institutes of Health. The findings, published in Diabetes Care, highlight the importance of adequate sleep in minimizing the risk for type 2 diabetes, which can develop when the body fails to effectively use a key hormone, insulin, to maintain healthy blood sugar levels.
The current study enrolled only women and sought to determine if a prolonged, mild restriction of sleep – a reduction of just 1.5 hours each night – increased women’s blood glucose and insulin levels. Insulin helps regulate glucose in the body, and when the body’s cells build resistance to insulin, they become less able to use it effectively and can cause a person’s risk for prediabetes and type 2 diabetes to rise dramatically.
For the study, researchers recruited 40 women, aged 20-75, who had healthy sleep patterns (at least 7-9 hours per night), normal fasting glucose levels, but had elevated risks for cardiometabolic disease due to having overweight or obesity or a family history of type 2 diabetes, increased lipid in the blood, or cardiovascular disease.
To establish a baseline for the study, women wore a sensor on their wrists to record their sleep and determine their typical sleep patterns for two weeks and kept nightly sleep logs. The women then completed two six-week study phases in a random order – one where they continued to follow their healthy sleep patterns, and one where sleep was restricted. In between they took a six-week break to recalibrate.
During the adequate sleep phase, participants maintained their typical bed and wake times. On average, they slept for 7.5 hours per night. In the sleep restriction phase, participants delayed their bedtime by 1.5 hours per night, while maintaining their typical waketime. During this phase, they slept 6.2 hours per night, which reflects the average sleep duration of U.S. adults with insufficient sleep. At the beginning and end of each study phase, participants completed an oral glucose tolerance test to measure glucose and insulin blood levels, along with an MRI scan to measure body composition.
The researchers found that restricting sleep to 6.2 hours or less per night over six weeks increased insulin resistance by 14.8% among both pre- and postmenopausal women, with more severe effects for postmenopausal women – as high as 20.1%. In premenopausal women, they found that fasting insulin levels rose in response to sleep restriction, while levels of both fasting insulin and fasting glucose tended to increase in postmenopausal women.
The researchers also looked at whether changes in body weight explained the changes they saw in insulin and glucose levels, as people tend to eat more in sleep-restricted states. However, they found that effects on insulin resistance were largely independent of changes in body weight, and once the women started sleeping their typical 7-9 hours per night again, the insulin and glucose levels returned to normal.
