Do you find yourself thirstier than usual, as well as hungry—even after eating? Frequently urinating or having a dry mouth? Fatigued or breathing more heavily? All of these are symptoms of diabetes, a disease that affects more than twenty-five million children and adults in the United States. In 2010, there were a little less than two million new cases of diabetes diagnosed among adults who were twenty years of age or older. It is roughly as common among men (11.8%) as it is among women (10.8%).
The key to understanding diabetes is to understanding the importance of insulin. Insulin is a hormone that plays a significant role in regulating blood sugar levels and enabling the body to convert sugar (also called glucose) into the energy needed for daily functioning. Some people with diabetes are unable to make insulin, which is referred to as Type 1 diabetes. The more common form of diabetes, however, is Type 2. Individuals with Type 2 diabetes do produce insulin, but it is produced in either insufficient amounts or the amounts that are produced are not recognized by the body’s cells, preventing the insulin from turning sugar into the energy needed for functioning. The symptoms for Type 2 diabetes often take a long time to develop, and in addition to the ones mentioned in the beginning, can include slow-healing cuts or sores, numbness or tingling in the hands and feet, and impotence.
Sleep Apnea and Diabetes: An Unhealthy Pair
For a while, most observations about sleep apnea and diabetes were that they often occurred simultaneously in those who were already obese, a condition common to both sleep apnea and diabetes. However, further investigation of the two has found that there is likely a direct relationship between them.
A 2008 literature review examined eight clinical studies concerning sleep apnea and diabetes and found an association between the severity of obstructive sleep apnea and alterations in participants’ glucose metabolism that were consistent with an increased risk for diabetes. A 2010 study published in the American Journal of Respiratory and Critical Care Medicine evaluated sixty diabetic patients and found that 77% of them had sleep apnea. Among the participants, increasing apnea severity was associated with poorer glucose control as measured by hemoglobin A1C levels. These results held true even after controlling for other factors that could explain the conditions, such as age, race, sex, body mass index, level of exercise, number of diabetic medications, years of diabetes, and total sleep time.
When an apneic event occurs during the night, the airway collapses and oxygen levels drop because the person has stopped breathing. This lowered oxygen level is referred to as hypoxia. Apneic events can also lead to arousals that can significantly fragment sleep over the course of the entire night. The combined effect of hypoxia and sleep fragmentation can lead to altered glucose (blood sugar) metabolism, a risk factor for diabetes.
Compared to normal sleep, the body undergoes a stress response due to the hypoxia and sleep fragmentation. Blood pressure and heart rates can increase, and breathing can momentarily speed up, particularly during arousals. Other changes include altering levels of leptin—a hormone that regulates energy intake and expenditure—and an increase in insulin resistance. The result of these changes due to sleep apnea—altered glucose metabolism, leptin levels, and increased insulin resistance—is an elevated risk for glucose intolerance, or type 2 diabetes.
Once diabetes has developed, the body is unable to get adequate energy from blood sugar to function appropriately. This means the control mechanisms for breathing during the night can be altered, resulting in the impaired breathing patterns typical of sleep apnea.
CPAP: Resolve Sleep Apnea, Improve Type 2 Diabetes
While sleep apnea and diabetes have a significant and mutually deteriorating relationship, the good news is that the opposite is also true—treating or improving the symptoms of one can often lead to an improvement in the other. For example, using diet and exercise to control diabetes may improve a person’s sleep.
The most common treatment for sleep apnea is Continuous Positive Airway Pressure (CPAP), which involves using air blown into a mask at a set pressure to keep the airway held open and prevent it from collapsing. To better understand how using CPAP to treat sleep apnea could improve diabetes, it is helpful to know how each condition can cause the other.
How does using CPAP to resolve sleep apnea affect diabetes? In a 2005 study of twenty-five patients with diabetes and obstructive sleep apnea, a significant decrease in hemoglobin A1C levels (used for measuring diabetes) was noted at the thirty and ninety day point of CPAP therapy. These decreases were correlated to the number of nights that participants used CPAP for at least four hours (the common standard for compliance).
The effects of CPAP in improving diabetes symptoms can occur fairly quickly. One study investigating the effects of CPAP on insulin sensitivity found that sensitivities were significantly improved after just two days of CPAP use. This effect was smaller in obese participants than non-obese ones, suggesting that insulin sensitivity for obese individuals may be regulated more by their obesity than by sleep apnea.