Using a simple device for eight hours a night to treat sleep apnea can help people with prediabetes improve their blood sugar levels and may reduce the risk of progressing to diabetes, according to a new study published online in the April 21, 2015, issue of theAmerican Journal of Respiratory and Critical Care Medicine.
About 57 million Americans have prediabetes, a disorder marked by blood sugar levels that are elevated but not sufficiently high to be considered diabetic. Prediabetics are at increased risk for developing diabetes, which can damage the eyes, kidneys, nerves and blood vessels and often leads to cardiovascular disease.
Many people with prediabetes also have untreated sleep apnea, although few of them are aware of it. The most widely accepted treatment for sleep apnea is continuous positive airway pressure (CPAP), a device that blows a constant pressure of air into the lungs through a tube and face mask during the night. This helps people breathe better while they sleep by keeping the upper airway open.
“Our study showed that CPAP in patients with prediabetes can lower their risk of progressing to diabetes when CPAP is used for eight hours, a full night’s sleep,” said the study’s lead author, Sushmita Pamidi, MD, a former fellow at the University of Chicago who is now on the faculty at McGill University in Montreal, Canada.
“Although eight hours of CPAP per night can be difficult to achieve in real-life, our results should provide a strong incentive for anyone with sleep apnea, especially prediabetic individuals, to improve adherence to their treatment for cardio-metabolic risk reduction,” she said.
People with sleep apnea, which is common among overweight and obese individuals, have repeated episodes where their upper airway closes during sleep. This can disrupt sleep and temporarily lower oxygen levels. It has been associated with an increased risk of cardiovascular diseases, such as hypertension and stroke, and may decrease their ability to regulate blood sugar levels. This increases the risk of diabetes.
For this study, the researchers recruited 39 middle-aged, overweight or obese volunteers with prediabetes and sleep apnea. Two-thirds of them (26) were randomly assigned to two weeks of CPAP treatment. The other 13 received a placebo — a pill containing no medicine — to be taken 30 minutes before bedtime. They were told the study would compare the two treatments.
All participants slept in the sleep laboratory and were closely monitored with all-night sleep recordings during the treatment period. Those assigned to CPAP wore the device for eight hours a night under continuous supervision by a technician. Before and after each treatment period, participants’ glucose metabolism was assessed by oral and intravenous glucose-tolerance tests.
The researchers also measured the stress hormone noradrenaline in the blood and continuously monitored blood pressure for 24 hours at home. All participants were permitted to leave the laboratory during the day and engage in their routine activities.
After two weeks, blood sugar control, as measured by an oral glucose tolerance test, improved for those in the CPAP group compared to the oral placebo group. In addition, the ability of insulin to regulate their blood sugar, estimated by the intravenous glucose tolerance test, was improved in the CPAP group compared to the oral placebo group. The CPAP group had, on average, 27 percent lower levels of the stress hormone, norepinephrine, as well as lower blood pressure than the oral placebo group.
“Despite the demonstrated efficacy of lifestyle interventions and the availability of many drug treatments, the economic and public health burden of diabetes remains enormous,” said Esra Tasali, MD, assistant professor of medicine at the University of Chicago and senior author of the study. “Assessment of sleep apnea should be considered in patients at high risk for diabetes and cardiovascular disease, since our study shows that treatment of sleep apnea can reduce these risks.”
The National Institutes of Health, plus the Diabetes Research and Training Center and the Institute for Translational Medicine at the University of Chicago funded this study. Additional authors include Kristen Wroblewski, Magdalena Stepien, Khalid Sharif-Sidi, Jennifer Kilkus and Harry R. Whitmore from the University of Chicago.
This news release outlines a recent paper reporting that a treatment for sleep apnea, called continuous positive airway pressure (CPAP), could help people with prediabetes who also have sleep apnea to regulate their blood sugar levels. (We have concerns about the release’s use of the term “prediabetes” that we discuss below in the review.) The release says that people with prediabetes and sleep apnea who use a CPAP device for 8 hours overnight have improved blood sugar control, lower levels of the stress hormone noradrenaline, and lower blood pressure. However, it did not, as the headline suggests, show that this approach had any actual impact on one’s risk of developing diabetes. The original study states the findings carefully, but the authors are less cautious when discussing the significance of the findings in the news release (examples below in the review). And while the release does a good job of explaining the study, it could do more to address costs and place its findings in context with past research that found little or no benefit for treating sleep apnea in people with prediabetes.
Sleep apnea is a condition that is common in people with diabetes, since both conditions are linked to obesity. Diabetes is increasingly being understood as a condition that is worsened by stress, and with sleep apnea, low oxygen levels at night and disrupted sleep put extra stress on the body’s metabolic system. This study was designed to test the concept that treating sleep apnea could reduce risk factors for the development of diabetes over a short period of time. The study is important because previous research has generally shown little effect from treating sleep apnea in people with prediabetes. The treatment for sleep apnea, a CPAP mask device worn all night, is hard for many people to tolerate and they may not use it for a full night’s sleep. The researchers investigated whether using CPAP for a full 8 hours improved glucose metabolism and found, unlike earlier studies, that there was a positive effect. They also explored whether blood pressure and stress hormones were reduced by CPAP treatment, a secondary goal of the study.
The release doesn’t address costs at all. This is a significant oversight, since testing to see if a person with diabetes has sleep apnea and, if so, should use a CPAP machine to treat it, can cost from hundreds to thousands of dollars.
The release is fairly vague on the benefits conferred on prediabetic patients using CPAP devices. For example, the release notes that “blood sugar control, as measured by an oral glucose tolerance test, improved for those in the CPAP group compared to the oral placebo group.” But this improvement is not quanitified. In addition, the study was not designed to show how likely it is that this improvement measured during a 2 week test period has a lasting impact on developing frank diabetes or, if so, how big that impact might be.
And although the original study paper was clear to state the limits of the findings, the first author exaggerates them in the news release. Consider the following comparison:
Paper: “In this proof of concept study, the CPAP treatment was limited to 2-weeks, and thus the study does not provide information on the potential effects of CPAP on glucose metabolism over a longer period of time. Importantly, in our study, CPAP was applied in the laboratory under continuous supervision, but 8-hour nightly CPAP use may be difficult to achieve in real-life conditions. Thus, our findings should be interpreted with caution, particularly in regards to CPAP recommendations to patients in clinical settings.”
Author in release: “Our study showed that CPAP in patients with prediabetes can lower their risk of progressing to diabetes when CPAP is used for 8 hours, a full night’s sleep.”
Benefits are further exaggerated (by implying that a population beyond that studied [everyone with sleep apnea, not just prediabetics with OSA] could benefit) in the following statement from the author in the release: “Our results should provide a strong incentive for anyone with sleep apnea, especially prediabetic individuals, to improve adherence to their treatment for cardio-metabolic risk reduction.”
While the release does not mention any harms associated with CPAP, that is likely because there are no significant health risks associated with the use of CPAP devices. However, it would have been worth noting that CPAP devices can often cause significant discomfort for users (and their bedmates), particularly at first. Getting CPAP to work can also require a lot of tinkering with the device.
The release does a good job of describing the study, addressing the overall number of participants (39), the number using CPAP (26), and those using placebo (13). The release also does a good job explaining the study’s methods and how it measured health effects in study participants. As noted above under Benefits, we thought the release failed to explain some important limitations to the research, but since we’ve already penalized the story for that shortcoming, we won’t do so again here.
This release shows no awareness of the debate over the diagnosis of “prediabetes,” unquestioningly labeling it a “disorder” affecting 57 million people. But if prediabetes signifies that you are “at risk for developing diabetes,” as the release says, wouldn’t it be more appropriate to call prediabetes a “risk factor” rather than a “disorder”? As this BMJ analysis notes, labeling someone as “prediabetic” carries the potential for harm, so we question any news release that uses the term casually, as this one does.
The release clearly identifies the sources of funding for the study, which were the National Institutes of Health and the University of Chicago’s Diabetes Research and Training Center and Institute for Translational Medicine. The release also quotes two researchers and makes clear that both researchers were authors of the paper describing the work.
The release does refer once to “lifestyle interventions and the availability of many drug treatments.” However, the release does not say what any of these treatment options are, much less compare the potential effectiveness of those treatment options to the use of a CPAP device. It would have been relatively easy to note that treatment options include changes in diet, increasing exercise, losing weight, and the oral blood sugar-lowering medication metformin.
The news release does not establish how easy or difficult it is to obtain treatment with a CPAP machine. Many people with prediabetes do not know they have sleep apnea. Diagnosis requires either an expensive overnight sleep study (not widely available) or sometimes, with a cheaper home sleep monitor (becoming more available). There are many insurance limitations on testing for sleep apnea. Once the condition is diagnosed, treatment is usually covered by insurance and provided by respiratory care supply companies in the home. Some discussion of this context would have been helpful.
This is one of the main limitations of the release. An online search shows that a number of studies have been done on the impact of CPAP use on patients with prediabetes and on patients with type 2 diabetes. The news release does not make clear how this most recent paper expands on the previous work — and it is important for releases like this one to place the new study in context.
If a release is going to include a headline that says, “Effective sleep apnea treatment lowers diabetes risk,” it should back that statement up with evidence. We believe the benefits of this proof-of-concept study are exaggerated in the release headline. This was not a randomized controlled study comparing 8 hours of CPAP in prediabetes for several months with a sham CPAP treatment, then looking at incidence of progression to diabetes months or years later — THAT would have justified this headline. The right headline would be something like, “CPAP can improve glucose metabolism.” Whether that leads to a decreased risk of future diabetes was not established by this study.