Sleep disturbances are an under-recognized factor in type 2 diabetes. Eve Van Cauter, PhD, a co-author of the “Impact of Sleep and Circadian Disturbances on Glucose Metabolism and Type 2 Diabetes” chapter in the NIDDK publication Diabetes in America, 3rd Edition, explains the relationship between poor sleep and diabetes and how health care professionals can advise their patients.

Q: What are sleep disturbances, and which ones are associated with insulin resistance and diabetes?

A: Sleep disturbances, which include sleep problems and diagnosed sleep disorders, are common in modern society. Probably the most common sleep disturbance is insufficient sleep—people are not in bed long enough. They want to take advantage of leisure opportunities, social networking, and our 24-hour society. High school-age children are probably among the most sleep-deprived segment of the population, and the sleep routines that they develop at that age set them on a trajectory of not prioritizing sleep as a pillar of health.

Irregular sleep is also common. About 16% of American workers do not have a regular daytime schedule, and their day-to-day sleep pattern is also irregular. They may be up until 2 a.m. one day, then recover the next day, and then have to leave very early in the morning another day. A related behavior is social jet lag, which refers to being sleep-deprived during the week, then trying to catch up during the weekend—a behavior common among adolescents and young adults.

Studies show that many sleep problems are associated with insulin resistance, prediabetes, and diabetes and have a significant impact on glucose tolerance. For example, there is experimental evidence that if you take healthy volunteers and force them into a schedule where sleep does not occur consistently during the night, the result is a decrease in glucose tolerance and insulin sensitivity.

The point here is that a modern lifestyle has brought about sleep irregularity, which adds to the risk factors for developing diabetes. That’s in addition to the established connection between type 2 diabetes and sleep disorders like insomnia and obstructive sleep apnea (OSA). OSA affects about two-thirds of people with type 2 diabetes. Its severity affects glycemic control in people who have diabetes—the more severe the OSA, the lower the insulin sensitivity.

Q: Can sleep problems or a sleep disorder increase the risk for developing type 2 diabetes?

A: Yes. Multiple studies have shown that repeated awakenings during the night, insufficient sleep, excessive sleep, and irregular sleep all promote glucose intolerance. Furthermore, if a person has prediabetes or diabetes, poor sleep will worsen the condition.

Sleep problems are also an issue for people with no other diabetes risk factors. Studies on mostly young, healthy adults without obesity or any diabetes risk factors have examined the effects of reduced sleep under controlled conditions in a laboratory. There was a consistent association with decreased insulin sensitivity in the range of 25% to 30% after as little as 4 to 5 days of insufficient sleep. So, there is reliable evidence that insufficient sleep has an adverse effect on glucose tolerance and can bring people who are otherwise healthy to developing prediabetes.

Subsequent cohort studies showed that after controlling for factors such as age, body mass index, being sedentary, and family history, and excluding people who have diabetes, participants who slept for short durations were about 40% more likely than those with 7 to 8 hours of sleep to develop diabetes.

As for people with sleep disorders, we know that moderate to severe OSA is a risk factor for developing type 2 diabetes. The increased prevalence of sleep disorders such as OSA parallels the rise in rates of obesity, and these two epidemics contribute to the dramatic increase in the prevalence of diabetes.

It’s worth noting that sleep disturbances, such as insufficient sleep or difficulty falling asleep or staying asleep, have an impact on diabetes risk similar to that of having a family history of type 2 diabetes.

Q: In people with type 2 diabetes, can treating sleep disturbances and disorders improve glycemic control?

A: We are still at the beginning of studying the impact of correcting sleep disturbances on glycemic control. We don't have many intervention studies yet. There have been a few studies of short sleepers who were asked to extend sleep for brief periods; extending their sleep duration improved their insulin sensitivity. There have also been some studies showing that extending bedtime in short sleepers may reduce hunger and appetite and promote weight loss. We need more studies in larger groups.

The one sleep disturbance that has been well studied is OSA. A number of studies have looked at continuous positive airway pressure (CPAP) to see whether this treatment can reduce glucose levels and improve glycemic control. The results have been mixed. Some clinical trials of CPAP compared with placebo treatment showed an effect on glucose metabolism or insulin sensitivity, but others did not.

The major issue is that if you do a study under real-life conditions, compliance with CPAP is generally poor. People wear their device for a few hours on most but not all nights, and that is considered excellent compliance. In laboratory studies, compliance can be optimized. In a proof-of-concept study, we treated patients with type 2 diabetes for 1 week. They had to sleep in the laboratory every night with the CPAP device, which was fitted as well as possible. Every little problem with the CPAP device was solved by the sleep technicians. After 1 week, we observed a decrease in morning glucose levels by about 12 milligrams per deciliter, which is clinically significant. It's the equivalent of what you can achieve with one drug.

Overall, the mixed results affect what happens in the clinic. CPAP devices have improved enormously, and there are devices now that are much more comfortable, smaller, lighter, quieter, and easier to tolerate. There are also dental appliances that can reduce the severity of OSA. Despite these advances, most health care professionals do not say, "You have to treat your sleep apnea because it's making your diabetes worse." Unfortunately, health care professionals have been somewhat discouraged from considering the treatment of OSA in diabetes as an important part of the therapeutic strategy.

Q: Should health care professionals screen patients for sleep problems? How should they advise patients who have poor sleep or a sleep disorder?

A: Health care professionals routinely ask about weight, family history of diabetes, and physical activity. But even an experienced diabetes specialist often will not ask patients any questions about sleep. Many health care professionals don't ask whether their patient has a day job or is coming to the morning clinic straight from work. Any kind of biochemical test result is affected if the night was spent awake.

There are questions that should be part of any patient history. What is your work schedule? Are you a good sleeper? What time do you go to bed? What time do you get up? And how about weekends? Do you have regular sleep times? There are short, simple questionnaires about sleep that the health care professional can ask people to fill out during an in-person or remote health visit. One, for example, is a sleep quality questionnaire that assesses habitual sleep duration and sleep quality. Another is a scale of daytime sleepiness that is sometimes revealing regarding the impact of OSA on daytime function. There is also a scale about sleep apnea itself. These questionnaires give health care professionals a good perspective on aspects of sleep that may need treatment or behavioral improvement. So, it's just a matter of making sleep part of the evaluation of the patient's history.

The American Diabetes Association’s annual recommendations mention insufficient sleep. OSA is mentioned among the factors that can impair glucose tolerance. That's a great first step. The International Diabetes Federation has also included some language regarding sleep in their guidelines. My hope is that more providers will become informed about these guidelines and will begin to apply these recommendations.

Q: Is there anything else health care professionals should know about sleep disturbances and patients with diabetes?

A: We are really looking at a triangle of metabolism, sleep, and nutrition. Food is available all the time—for some people, instead of having three meals a day, they consume excess calories in addition to their normal meals. They snack as the day progresses and into the night. This reduces the duration of the overnight fast and affects glucose regulation. By modifying sleep duration, you will encourage dietary changes that in and of themselves can affect glucose metabolism.

Do you screen your patients with diabetes for sleep problems? Share below in the comments.