At the American Thoracic Society 2007 International Conference, held in San Francisco May 18-23, numerous studies on respiratory and sleep medicine were presented. Highlights from three documenting the risks associated with obstructive sleep apnea and obesity follow.
Long-Term Study Shows OSA Heightens Risk of Heart Attack, Death
Obstructive sleep apnea increases a person's risk of having a heart attack or dying by 30 percent over a period of four to five years, according to a new study.
The more severe the sleep apnea at the beginning of the study, the greater the risk of developing heart disease or dying, the results revealed.
The study, called “Obstructive Sleep Apnea Is Associated with an Increased Risk of Coronary Artery Disease and Death,” included 1,123 patients referred for sleep apnea evaluation. They underwent an overnight sleep study to determine if they had sleep apnea. Over the next four to five years, they were followed to see how many had any heart disease events (heart attack, coronary angiography or bypass surgery) or died.
“While previous studies have shown an association between sleep apnea and heart disease, ours is a large study that allowed us to not only follow patients for five years and look at the association between sleep apnea and the combined outcome of heart attack and death but also adjust for other traditional risk factors for heart disease,” said researcher Neomi Shah, M.D., of Yale University.
“We recommend that patients who experience symptoms of obstructive sleep apnea — excessive daytime sleepiness, or snoring along with breathing pauses — consult their physician,” said Shah. “There is some evidence to make us believe that when sleep apnea is appropriately treated, the risk of heart disease can be lowered.”
In OSA, 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.
Sleep apnea triggers the body's “fight or flight” mechanism, which decreases the amount of blood pumped to the heart. Repeated episodes every night for a few years can starve the heart of enough oxygen when it is combined with the body's decreased oxygen intake due to the frequent breathing stoppages during the night, Shah said.
According to the researchers, CPAP is the most effective treatment for sleep apnea and has proved successful in many cases in providing a good night's sleep, preventing daytime accidents due to sleepiness and improving quality of life.
More Pounds = Worse Asthma?
Obese people are significantly more likely to have persistent or severe persistent asthma than their thinner counterparts, according to “Body Mass Index as a Predictor of Asthma Severity in Adults with Asthma.”
The study looked at 3,059 adults with asthma, who were divided into three groups based on their body mass index: non-overweight, overweight and obese. Compared with non-overweight asthma patients, obese patients (BMI 30) were more likely to report having continuous symptoms, have more ER visits, miss more days of work, use more rescue inhaler medications and use inhaled steroids to control asthma.
Obese patients were 66 percent more likely to report having asthma symptoms all of the time, 47 percent less likely to be in asthma remission and 52 percent more likely to have severe persistent asthma than non-overweight people with asthma. Obese asthmatics were also 36 percent more likely to miss more than two days of work per year due to asthma than non-overweight asthma patients.
“There have been a number of studies on obesity and asthma prevalence, but until now there has been little data on obesity and asthma severity,” according to lead researcher Brian Taylor, M.D., of Emory Crawford Long Hospital in Atlanta.
The studies that have been done have been small, but this study took data from the National Asthma Survey, which includes 5,741 asthmatics, Taylor noted. “We had enough data to adjust for other factors, such as gender, race, income and employment status, and ensure that these factors were not playing a role in the results. Even after taking these variables into account, the association between obesity and asthma severity still held,” Taylor said.
Taylor added that this study, like many previous studies, shows the link between asthma and obesity is more prominent in women. “A big part of that is simply that 70 percent of the study subjects were women,” he said. “We did find a statistically significant association between obesity and asthma severity in men, too.”
While it's not known for sure how asthma and obesity are linked, Taylor said that one potential mechanism seems to be an association between the hormone leptin, which is produced by fat cells and plays a role in body weight regulation, and inflammation of airways seen in asthma. Obesity also may impact the lungs in other ways to increase the risk of asthma.
Other studies suggest that asthma incidence could be reduced by interventions targeting overweight and obesity. Taylor and colleagues are now looking at whether patients who undergo bariatic, or weight-loss, surgery experience an improvement in airway function compared with obese patients who don't have the surgery.
Sleep Apnea May Increase Danger Of Diabetes
Researchers at the Yale University School of Medicine have found that patients with OSA are at increased risk for developing type II diabetes, independent of other risk factors.
In a study called “Obstructive Sleep Apnea as Risk Factor for type II Diabetes,” the researchers looked at 593 patients at the VA Connecticut Health Care System referred for evaluation of sleep-disordered breathing. Each patient spent a night in a sleep laboratory to undergo a polysomnography sleep study.
The researchers followed the subjects for up to six years and found that patients diagnosed with OSA had more than two-and-a-half times the risk of developing diabetes compared with those without the nighttime breathing disorder. The patients were then divided into groups based on the severity of their sleep apnea, and the more severe a patient's sleep apnea, the greater the risk of developing diabetes.
“Our next step will be to determine whether the treatment of sleep apnea can improve an individual's diabetic parameters and consequently the negative health effects of diabetes,” said researcher Nader Botros, M.D., of Yale University.
Botros said that although it is not known exactly what the link is between OSA and diabetes, it is thought that when sleep apnea activates the body's “fight-or-flight” response, this triggers a cascade of events, including the production of high levels of the hormone cortisol that ultimately leads to insulin resistance and glucose intolerance, 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 in order to develop additional preventive strategies.
“Understanding the link between sleep-disordered breathing and diabetes may represent one such approach.”
With 18,000 members, the American Thoracic Society works to advance lung, critical care and sleep medicine. For more information, visit www.thoracic.org.
