With commentary by Yanping Li, MD, PhD, Harvard T.H Chan School of Public Health, and Minisha Sood, MD, director of inpatient diabetes, Lenox Hill Hospital, New York City.
Women who have sleep problems such as insomnia have a higher risk of developing type 2 diabetes, new research finds. Worse, the more types of sleep problems a woman has, the higher her risk, says study researcher Yanping Li, MD, PhD, a research scientist at Harvard School of Public Health.
"Overall, it's around 45% higher," she says of the increased risk for diabetes with women's sleeping problems. However, Dr. Li and her team looked at four different sleeping problems including trouble falling or staying asleep, getting fewer than six hours of sleep, snoring frequently, having sleep apnea (in which breathing stops for a short period) or doing shift work (associated with sleep problems). The greater the number of sleep problems, the higher the risk, she says. (They looked at two different study groups; in one, they had information on apnea; in the other, shift work.)
"If they had all four sleep disorders, their risk increased four times [compared to those who did not have sleep problems]," she says. The study, which tracked more than 133,000 women, is published Jan. 28 in the journal Diabetologia.
Sleeping problems have been linked with type 2 diabetes in other research, but Dr. Li says to her knowledge no previous studies have looked at the combined effect of having several sleep disorders, as her team did.
While she can document the risk and the extent of it, she cannot yet explain it. "We found an association, but it's not clear yet why it's happening," says Dr. Li. One speculation, she says, is that people who can't sleep normally may not have a healthy endocrine system (the collection of glands secreting hormones that regulate metabolism and other bodily functions).
In the study, the researchers collected information on the more than 133,000 women taking part in the Nurses' Health Study and the NHSII, spanning the years 2000 to 2011. During a follow up of up to 10 years, more than 6,400 women learned they had type 2 diabetes.
When they adjusted for lifestyle factors at the study's start that may affect diabetes risk (such as smoking status, alcohol intake, physical activity, family history of diabetes) they found the overall risk increased by 45%. When they then took into account factors such as high blood pressure, depression, and a high body mass index or BMI, which can all raise the risk of diabetes, the overall increased risk fell to 22%.
However, as the sleeping issues accumulated, so did the risk, as Dr. Li found. "If they have one sleep disorder, their risk increased about 40%," she says, With two, the risk doubled, and with three, it tripled, she says. All four increased the risk four-fold, she found.
Some questions can't be answered, Dr. Li says, such as how long a period of sleep deprivation becomes dangerous for diabetes risk. While her team looked at a 10-year period, they did not collect all the data each year. For instance, shift work information was recorded in one study at the start, when women reported if they had worked night shifts for six or more months in the six previous years.
Dr. Li can't say from the study whether the risk of diabetes can be reduced or reversed by paying more attention to sleep or improving it by getting care at a sleep lab, for instance. And she can't give an exact answer about how much the risk goes up if you have, for instance, high blood pressure and a sleep issue, or high blood pressure and many sleep issues.
One thing is for sure, she says. "Doctors should pay more attention to those who complain of sleep disorders." Patients should expect to be taken seriously by their primary care doctor if they complain about sleep issues, Li says.
The findings are no surprise to Minisha Sood, MD, director of inpatient diabetes at Lenox Hill Hospital, New York City, who reviewed the study. The findings are evidence that ''we all need to reassess and re-analyze our priorities," she says. People tend to take lack of sleep for granted, especially if they work long hours and have other responsibilities, she says. Some simply don't realize how important good sleep is, she says.
However, she says, it is well known that when sleep is lost, levels of the stress hormone cortisol go up. "Cortisol is essential to live," says Dr. Sood. "It's part of the flight or fight response."
High cortisol over time, however, can lead to high blood pressure and high cholesterol and raise the risk of diabetes, she says. She counsels patients to pay attention to sleep in an effort to turn around or reduce the risk, even though the study can't definitely say whether it will work. Even a few nights of restricted sleep can raise blood sugar, Dr. Sood says, but of course a few days' sleep deprivation does not lead to diabetes, she adds.
Getting good sleep, Dr. Sood finds, can trigger other good health habits. People who feel rested may feel more like exercising, she says, and that could help them lose excess weight, in turn reducing their diabetes risk.
1. Study abstract: http://www.ncbi.nlm.nih.gov/pubmed/26818148
2. High blood pressure, diabetes risk: http://www.diabetes.org/are-you-at-risk/lower-your-risk/bloodpressure.html