Findings highlight insufficient sleep as a modifiable risk factor for type 2 diabetes

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.

“Women report poorer sleep than men, so understanding how sleep disturbances impact their health across the lifespan is critical, especially for postmenopausal women,” said Marishka Brown, Ph.D., director of the National Center on Sleep Disorder Research at the National Heart, Lung, and Blood Institute (NHLBI), which co-funded the study with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), both part of NIH.

Previous studies have shown that sleep restriction can elevate risk for conditions such as cardiovascular disease, hypertension, and disordered glucose metabolism, which can lead to insulin resistance and type 2 diabetes. However, many of those studies were done only in men or focused on short-term, severe sleep restriction.

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.

“What we’re seeing is that more insulin is needed to normalize glucose levels in the women under conditions of sleep restriction, and even then, the insulin may not have been doing enough to counteract rising blood glucose levels of postmenopausal women,” said Marie-Pierre St-Onge, Ph.D., associate professor of nutritional medicine and director of the Center of Excellence for Sleep and Circadian Research at Columbia University Vagelos College of Physicians and Surgeons, New York City, and senior author on the study. “If that's sustained over time, it is possible that prolonged insufficient sleep among individuals with prediabetes could accelerate the progression to type 2 diabetes.”

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.

“This study provides new insight into the health effects of even small sleep deficits in women across all stages of adulthood and racial and ethnic backgrounds,” said Corinne Silva, Ph.D., Program Director in the Division of Diabetes, Endocrinology, & Metabolic Diseases at NIDDK. “Researchers are planning additional studies to further understand how sleep deficiency affects metabolism in men and women, as well as explore sleep interventions as a tool in type 2 diabetes prevention efforts.”