Restless Sleep, Restless Blood Sugar

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By Dianna Douglas

Kristen Knutson, PhD, recently added to the growing body of research from the University of Chicago on the long-term consequences of skimping on sleep. She found that diabetics who sleep poorly have a harder time controlling their insulin and glucose levels than diabetics who sleep well. The research was published in the journal Diabetes Care. We conducted an extended interview with Kristen Knutson about her research, and below are some of the highlights.

Q: Why study diabetes and chronic sleep problems?

A: Many of our laboratory studies, led by Dr. Eve Van Cauter, have shown that restriction of sleep is associated with alterations in glucose metabolism. Usually, these lab studies are a week. But we wonder about the long-term effects of being a chronic short sleeper.

We think that chronic poor sleep could put people at risk of many health problems, including diabetes.

Q: How did you design your study?

A: We used data from an epidemiologic study called CARDIA (coronary artery risk development in young adults). It started in 1985, and has been going on for more than 20 years.

We gave the participants wrist activity monitors—it’s like a wristwatch that measures the subject’s sleep duration. The participants wore the activity monitors for three nights in a row. A year later, they wore the monitors three more nights. So we had a total of six days of data.

We also asked them about their sleep. Did they wake up frequently during the night, three or more times per week? Did they have trouble falling asleep?

To get the measurements of their fasting blood glucose and fasting blood insulin, we used the data from the CARDIA study, in which the participants gave fasting blood samples. Their fasting blood glucose and insulin give us an estimate of insulin resistance.

Q: Explain your most striking findings, especially with the diabetics who slept poorly.

A: We saw more significant associations between measures of sleep and glucose metabolism markers in the patients with diabetes. In particular, we saw that poor sleep quality was associated with higher fasting glucose and greater estimated insulin resistance. So poor sleep quality meant worse control of their blood glucose levels.

Also, we separated people with and without insomnia. Among the people with type 2 diabetes, those who also had insomnia had worse glucose levels and greater estimated insulin resistance. That suggests that it’s not just sleep duration that’s important, which laboratory studies have shown. But sleep quality is important as well.

The data show that people with diabetes who are poor sleepers will have a more difficult time controlling their glucose levels.

Q: Does this mean that sleeping poorly makes diabetes worse?

A: It could go the other way. It could be that people who are having trouble controlling their glucose will have more complications, more pain, more need to get up in the middle of the night to urinate, and therefore they’re not sleeping as well. What we need to do now is find people with diabetes who aren’t sleeping well, and see if improving their sleep also improves their glucose metabolism.

This study is observational, but suggests that there is a relationship between poor sleep and controlling glucose. We don’t know which factor leads to which outcome.

Q: What does it mean for a diabetic to have a difficult time managing their disease?

A: People who have a more difficult time controlling their glucose levels have a greater risk of complications, a reduced quality of life, and a reduced life expectancy. The ability to control their glucose and manage the disease is really important for a diabetic’s long-term health. If there’s anything that we can do to help them control their glucose, then we should do it. It’ll help their lives in the long run.

Q: Do you think this association with poor sleep is true for people who already have diabetes?

A: We already know that people with diabetes have more trouble with their sleep than healthy people. Between 60 and 80 percent of people with type 2 diabetes have obstructive sleep apnea.

You can live well with diabetes if you’ve got it under control and if you’ve careful about managing your glucose metabolism. It can be tricky. So if sleep is a factor and we can improve sleep, we can help them control their glucose levels and control their disease.

Q: In people without diabetes, insulin resistance isn’t affected by poor sleep?

A: We didn’t see significant associations in people without diabetes. One explanation is that the people with diabetes already have an impaired glucose metabolism system, so they may be more sensitive to sleep disturbances, if sleep disturbances do indeed lead to problems with glucose metabolism.

Q: What’s next?

A: The next step is to try to restore sleep quality or duration in people and see if we can improve their health– i.e. reduce their diabetes risk if they don’t have it already. If they do have it, can we help them control their glucose metabolism? We are already studying people with diabetes and sleep apnea, to see if the sleep apnea mask helps improve the markers of glucose metabolism. We need to do more of those studies.

We’ve shown with laboratory studies that impairing their sleep is bad for health, now we need to do the opposite – extend sleep or restore sleep and see if it helps.

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Knutson KL, Van Cauter E, Zee P, Liu K, & Lauderdale DS (2011). Cross-Sectional Associations Between Measures of Sleep and Markers of Glucose Metabolism Among Subjects With and Without Diabetes: The Coronary Artery Risk Development in Young Adults (CARDIA) Sleep Study. Diabetes care, 34 (5), 1171-6 PMID: 21411507

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