Updated October 17, 2007

Sleep Apnea and Type 2 Diabetes:
A Vicious Circle

by Ralph Pascualy, M.D.

Elevated fasting glucose. Sleep apnea is independently associated with glucose intolerance and insulin resistance, whether or not a person is obese. Impaired glucose tolerance has also been linked with sleep restriction, insufficient sleep, and difficulty maintaining sleep, all of which typically occur with snoring and sleep apnea.

Visceral fat. Excess body fat, particularly in the abdominal area, is a good predictor of sleep apnea. Two-thirds of people who snore or have been found to have sleep apnea are obese. The severity of sleep apnea increases with increasing body-mass index.

High blood pressure. The risk of high blood pressure also increases with increasing severity of sleep apnea, and it has additionally been linked with insulin resistance.

Dyslipidemia. Elevated triglycerides and reduced HDL cholesterol are common among people with Type 2 diabetes, and they correlate with even mild sleep apnea, independent of body-mass index.

Sleep apnea is independently associated with each of the five metabolic syndrome conditions. The metabolic syndrome may be made worse by both untreated sleep apnea and untreated diabetes.

Treatment
When people with sleep apnea and Type 2 diabetes are treated with continuous positive airway pressure (CPAP, a common treatment for sleep apnea), the resulting improvement in their diabetes control leaves little doubt that sleep apnea may play a role in the functional changes that accompany Type 2 diabetes.

A CPAP device consists of a small mask that fits over the nose, or in some instances the mouth, and is connected to a machine that creates a slight air pressure in the throat to keep the airway open. A number of studies have examined its use.

For example, a study published in the Journal of Clinical Endocrinology & Metabolism in 1994 used CPAP therapy in a group of men and women who had Type 2 diabetes and sleep apnea. After four months of CPAP therapy, their sensitivity to insulin improved significantly.

A study published in the journal Respiration in 2004 measured the effects of CPAP therapy on insulin sensitivity in nine obese people with Type 2 diabetes and sleep apnea. These people had achieved good blood glucose control by means of either medication and diet or diet alone. Nonetheless, after three months of CPAP therapy, their insulin sensitivity improved significantly.

In yet another study, this one published in the Archives of Internal Medicine in 2005, use of CPAP therapy for at least four hours a day over one to four months led to improvements in blood glucose levels after meals in 25 people with Type 2 diabetes and sleep apnea. In addition, it led to lower glycosylated hemoglobin (HbA1c) levels in 17 people whose starting HbA1c was higher than 7%. The HbA1c test is a measure of blood glucose control over the previous 2–3 months. A normal, nondiabetic HbA1c level is between 4% and 6%.

In people with both sleep apnea and diabetes, therefore, CPAP therapy is an effective element in a treatment regimen where the objectives are normalized sleep and improved blood glucose control.

Further potential benefits from the treatment of snoring and sleep apnea may include the following:

• Improved control of high blood pressure
• Reduction in inflammatory response
• Reduced risk of fatal and nonfatal cardiovascular events (such as heart attacks)
• Reduced utilization of health-care resources

Improved quality of life is a common but frequently underappreciated benefit of CPAP therapy. People who use their CPAP device regularly experience improved sleep quality and have less fatigue, more energy, and improved coping capability. Depression, a common accompaniment of sleep apnea, may be replaced by a more positive mood. All of these changes enable a person to engage more readily in daily activities. Weight loss and improved fitness then become real possibilities, with their added beneficial effects on glucose tolerance.

Dr. Pascualy is the Medical Director of the Swedish Sleep Medicine Institute at the Swedish Medical Center in Seattle. He is the coauthor of the book Snoring and Sleep Apnea: Sleep Well, Feel Better (3rd edition), published by Demos Medical Publishing in 2000.

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