Women, particularly those who are postmenopausal, who sleep less than the recommended 7 hours per night may have impaired insulin sensitivity regardless of their degree of adiposity, a randomized crossover trial reveals.
The research was published recently in Diabetes Care.
Nearly 40 women were randomly assigned to either restricted sleep or adequate sleep for 6 weeks, then crossed over to the other sleep condition. During sleep restriction, women slept an average of 6.2 hours per night vs 7-9 hours per night.
Both fasting insulin levels and insulin resistance were significantly increased during sleep restriction, with the effect on insulin resistance particularly notable in postmenopausal women. This was independent of adiposity and changes in adiposity.
"What we're seeing is that more insulin is needed to normalize glucose levels in the women under conditions of sleep restriction," said senior author Marie-Pierre St-Onge, PhD, director of the Center of Excellence for Sleep and Circadian Research at Columbia University Vagelos College of Physicians and Surgeons in New York, in a release.
"Even then, the insulin may not have been doing enough to counteract rising blood glucose levels of postmenopausal women," she stated.
Prolonged Lack of Sleep May Accelerate Diabetes Progression
St-Onge added, "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."
St-Onge told Medscape Medical News it was crucial to show the impact of sleep restriction in a randomized study, because "observational studies don't provide information on causality."
The study did not rely on people "living in our clinical research facility," but instead enrolled individuals who were "living their lives," and the reduction in sleep achieved was "similar to what is seen in the general population with sleep," she said.
St-Onge therefore believes the findings indicate that sleep has been overlooked as a contributory factor in insulin sensitivity.
Robert Gabbay, MD, PhD, chief scientific and medical officer at the American Diabetes Association (ADA), told Medscape Medical News that this is an "important study" that "builds on what we have seen on the importance of sleep for metabolic outcomes and diabetes."
He continued, "There have been several studies showing the association of sleep and diabetes, but that does not necessarily mean cause and effect."
On the other hand, Gabbay said, "randomizing people can help see sleep influences on key metabolic measures of diabetes," which "helps to build a stronger case that sleep disturbances can cause worsening metabolic health."
He emphasized that both the quantity and quality of sleep are "critical for optimal diabetes health" and highlighted that the ADA's Standards of Care "recommends screening for sleep issues and counseling to improve sleep."
"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," commented Corinne Silva, PhD, program director in the Division of Diabetes, Endocrinology, and Metabolic Diseases at the National Institute of Diabetes and Digestive and Kidney Diseases, which co-funded the study.
The authors note that more than one third of adults sleep less than the recommended 7 hours per night, which is "concerning given robust associations of short sleep with cardiometabolic diseases."
Moreover, "women report poorer sleep than men," explained Marishka Brown, PhD, director of the National Center on Sleep Disorders Research at the National Heart, Lung, and Blood Institute, which also co-funded the study.
"So understanding how sleep disturbances impact their health across the lifespan is critical, especially for postmenopausal women," she said, particularly because previous studies have not reflected real-world sleep patterns or have focused on men.
The researchers conducted a trial to evaluate the causal impact of prolonged, mild sleep restriction on cardiometabolic risk factors in women as part of the American Heart Association Go Red for Women Strategically Focused Research Network.
They recruited metabolically healthy women aged 20-75 years who were at increased risk for cardiometabolic disease due to having either overweight or class I obesity or at least one parent with type 2 diabetes, hyperlipidemia, or cardiovascular disease.
They were also required to have a habitual total sleep time on actigraphy of 7-9 hours per night and low risk for sleep apnea. Exclusion criteria included excessive caffeine intake, a significantly advanced or delayed sleep phase, shift work, and travel across time zones.
The participants were randomly assigned to either adequate sleep, defined as 7-9 hours per night, or sleep restriction, defined as a reduction in sleep duration of 1.5 hours per night, for 6 weeks. They were then crossed over to the other sleep condition.
Assessments, including MRI and oral glucose tolerance tests, were performed at baseline and at the end of each study phase.
The researchers report on 38 women who took part in the trial, of whom 11 were postmenopausal. The mean age was 37.6 years; 31.6% self-identified as Black and 26.3% as Hispanic. The mean body mass index was 25.5.
Postmenopausal women had a higher mean age than other women, at 56.1 years vs 30.1 years, and a higher baseline fasting blood glucose, at 5.26 mmol/L (94.68 mg/dL) vs 4.70 mmol/L (84.6 mg/dL).
The team reported that compliance with the sleep protocol was "excellent," with women during sleep restriction having a reduction in total sleep time of 1.34 hours per night vs women in the adequate sleep arm (P < .0001).
Sleep restriction was also associated with significant increases in fasting plasma insulin vs adequate sleep, at a beta value of 0.68 pmol/L (P = .016), and significantly increased Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) values (beta = 0.30; P= .016).
The impact on HOMA-IR values was significantly more pronounced in postmenopausal than menopausal women, at beta values of 0.45 vs 0.27 (P for interaction = .042).
Sleep restriction had no significant effect on fasting plasma glucose levels, and the association between sleep duration and cardiometabolic parameters was not modified by the proportion of either total or visceral adipose tissue, or by changes in adiposity.
This clinical trial was supported by the American Heart Association, a National Institutes of Health Clinical and Translational Science Award to Columbia University, and NY Nutrition Obesity Research Center. Individuals authors received support from the National Heart, Lung, and Blood Institute and the National Institute of Diabetes and Digestive and Kidney Diseases. No relevant financial relationships were declared.
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