Sleep Apnea: Epidemiology
It is estimated that sleep apnea affects 100 million people worldwide. Approximately 80 percent of those people are currently undiagnosed. This is most probably due to mild and ambiguous symptoms (in less severe cases) that neither the patients or doctors attribute to apnea.
Prevalence in the United States
According to a 2009 study, seven percent of Americans suffer from sleep apnea. Adults make up most of the sufferers, with nearly 20 percent of adult males and nine percent of adult females afflicted with some form of the disease at some time in their lives. Moderate-to-severe apnea affects nine percent of males and four percent of females. Two percent of children are also affected by sleep apnea, most of these children being infants under one year of age. Another source (Medicinenet.com) says 4% of men and 2% of women have OSA and refers to a study showing apnea develops in 1.5% of adults every year. The federal government estimates only a quarter of those with obstructive apnea sought medical evaluatrion in the 2005-2008 period.
Changes in Prevalence
Apnea has been on the rise in the United States, partly because of better diagnosis and partly because of increased obesity rates. In the early 90's, approximately 3 percent of the general population had apnea. In 2002, a study printed in the "American Journal of Respiratory and Critical Care Medicine" found that number had risen to five percent. A 2009 survey found the percentage had increased again by two percent. This shows us that sleep apnea has increased more than twofold in a little under twenty years. The increase in apnea is directly correlated with the rise in obesity within the United States although increased awareness and better diagnosis is part of it, too. The government's Healthy People intitiative claims that 25.5% of Americans with the symptoms of OSA seek medical attention.
Differences in Populace Based on Age, Race, and Gender
Sleep apnea is most prevalent in middle-aged males. Males are between two and three times as likely to develop apnea than women. This appears to be due, at least in part, to physiological and anatomical differences between the genders. Males typically have a larger neck circumference and a longer pharyngeal airway, which make them more susceptible to sleep apnea. Males also have a higher apneic threshold, due to certain male hormones, according to a study done by Safwan Badr in 2005 (Reference 4).
There are also differences between ethnic groups. African Americans are more than twice as likely to get apnea than Caucasians. This difference has been found to be caused by genetic factors and is independent of other respiratory or weight-related illnesses, says the American Lung Association. Pacific Islanders and Hispanics also develop sleep apnea at a higher rate, though it appears to be due to increased obesity rates in those ethnic groups. Prevalence in Asians is similar to that in Caucasians, but the causation is different. In Asians, sleep apnea more often develops due to faciocranial features and is not associated with obesity.
The incidence of obstructive sleep apnea goes up with age and is most commonly seen in people between the ages of 40 and 60. Curiously, after age 60, incidence goes down. People in their 70s have only twice the incidence of 20-year-olds. Children sometimes have apnea, although it is more rare than in adults. Children born with facial deformities can get apnea. Childhood apnea is often solved by removing the tonsils.
At Risk Groups
Pregnant women, smokers and those suffering from obesity have higher rates of apnea.
A staggering 78 percent of pregnant women experienced symptoms indicative of sleep apnea at some point in their pregnancy, most of them in the third trimester. This seems to be due to a combination if enlarged blood vessels, effects of hormonal changes on the body, and weight gain.
Smokers face an elevated risk. They are three times as likely to
develop apnea as nonsmokers. The increase is the result of
increased upper airway inflammation and fluid retention, both of which are caused by smoking. The increased risk, however, is temporary, and goes away once a smoker quits smoking.
The biggest correlate of sleep apnea is obesity. Moderate to severe sleep apnea can be found in 40 percent of obese individuals and 70 percent of sleep apnea sufferers are medically defined as obese. There is no solid evidence as to why obesity has such a profound effect on apnea, but a variety of factors are theorized to come in to play. Research indicates increased hormones found in obese individuals negatively impact chemoreflex, while increased weight and fat deposits affect airway anatomy and function.
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