The nighttime breathing disorder known as sleep apnea increases a person’s risk of having a heart attack or of dying by 30 percent over a period of four to five years, according to a Yale School of Medicine study.
These findings and another Yale study linking sleep apnea and diabetes were presented this week at the American Thoracic Society 2007 International Conference in San Francisco.
In obstructive sleep apnea, the upper airway narrows, or collapses, during sleep. Periods of apnea end with a brief partial arousal that may disrupt sleep hundreds of times a night. Obesity is a major risk factor for sleep apnea.
Sleep apnea triggers the body’s “fight or flight” mechanism, which decreases the amount of blood pumped to the heart, said Neomi Shah, M.D., clinical fellow in the Department of Internal Medicine, pulmonary section. She conducted the study linking heart disease and sleep apnea.
Shah’s study included 1, 123 patients referred for sleep apnea evaluation. They were followed for the next four to five years to see how many had a heart attack, coronary angiography, bypass surgery, or died. Previous studies showed a correlation between sleep apnea and heart disease, but this is the first large study to follow patients for five years and to adjust the findings for other traditional risk factors for heart disease.
The most effective treatment for sleep apnea is a technique called nasal CPAP (continuous positive airway pressure), which delivers air through a mask while the patient sleeps, keeping the airway open. “There is some evidence to make us believe that when sleep apnea is appropriately treated, the risk of heart disease can be lowered,” Shah said.
In another Yale study presented at the conference, researchers found patients with sleep apnea are at increased risk for developing Type II diabetes, independent of other risk factors. The study looked at 593 patients at the VA Connecticut Health Care System referred for evaluation of sleep-disordered breathing.
The researchers followed the patients for up to six years and found that patients diagnosed with sleep apnea had more than two-and-one-half times the risk of developing diabetes compared with those without the nighttime breathing disorder. The more severe a patient’s sleep apnea, the greater the risk of developing diabetes.
Nader Botros, M.D., a fellow in the pulmonary section, said the exact reasons for the link between sleep apnea and diabetes are not known, but researchers suspect that when the “fight or flight” response is triggered by sleep apnea, a cascade of events occurs, including the production of high levels of the hormone cortisol that ultimately leads to insulin resistance and glucose intolerance. These are pre-diabetic conditions that, if left untreated, can lead to the development of diabetes. Low oxygen levels also appear to play an important role.
“The impact of diabetes on public health is great,” Botros said. “Diet and exercise, along with a medication regimen, are the mainstays of treatment, but unfortunately diabetes remains a major public health challenge. New approaches are needed to better understand the risk factors for diabetes. Understanding the link between sleep-disordered breathing and diabetes may represent one such approach.”