Introduction

Sleep apnea is usually spotted by the subject's sleeping partner; the person stops breathing during the night, often many times, for anywhere from 10 seconds up to a minute. It's usually accompanied by snoring. The person may not be aware he has a problem, but invariably there is daytime sleepiness. Sleep apnea should be treated, because it's associated with an increased risk of high blood pressure, heart disease, and mental decline. So a recent report in the Journal of the Medical Association is helpful in teaching us about the possible risk factors and the frequency of sleep apnea.

What was done

The Cleveland Family Study is being done to study obstructive sleep apnea over a 5-year period in people aged 18 or over, living in an urban community in Cleveland, Ohio, USA. After various selection conditions were fulfilled, just over 250 participants had two overnight sleep monitoring done at home, 5 years apart.

In addition to the sleep examinations, they completed questionnaires, had a physical exam to see if their tonsils were enlarged or if there was another cause of upper airway obstruction, and had their blood pressure, weight, height, serum cholesterol, and other items measured.

The main measure of apnea was what is known as the Apnea-Hypopnea Index, or AHI, which is the total number of episodes of either apnea or hypopnea (poor, shallow respiration) divided by the number of hours of sleep; this is measured by the sleep monitor apparatus.

People with an AHI of 5 or over at the first sleep exam were excluded from further study. The 250+ subjects remaining in the study had AHI levels below 5, indicating that they didn't have evidence of sleep apnea at the start of the study.

What was found

Three quarters of the participants were women, almost half of them snored, and one in 6 had cardiovascular disease (high blood pressure, coronary heart disease). On average, they were overweight - their body mass index (BMI) was 27.6. Their average age was 37 years.

At the second visit, 5 years later, 180 participants (about 2 in 3) still had AHI values below 5, and were therefore not considered to have sleep apnea. In the others, 20% had an AHI between 5 and 10, 6% an AHI between 10 and 15 (which indicates mild to moderately severe sleep apnea), and 10% had an AHI over 15 (moderately severe sleep apnea). This suggests that over a third of the participants had developed at least some degree of sleep apnea during the 5-year period.

Further analyses showed that the occurrence of sleep apnea was significantly more likely with increasing age, increasing weight, being a man, increasing girth, and increasing serum cholesterol level. Race, large tonsils, smoking, alcohol use, and having a family member with the condition didn't seem to influence the likelihood of sleep apnea.

The increased likelihood of men being at risk for sleep apnea disappeared after the age of 50, and that of being overweight was gone after age 60.

What's the importance of all this?

In discussing their results, the scientists point out that around 2.5% of sleep apnea subjects with an AHI over 15 can get better 'on their own', having a second AHI level of 5 or below. They therefore adjusted the frequency of moderately severe sleep apnea in this study from 10% down to 7.5%.

Nevertheless, the high frequency of this disease in a young group of town-dwellers is disturbing, because of the increased risk of heart disease and mental decline. It's another reason to avoid being overweight and having a high serum cholesterol. Fortunately, a treatment called 'continuous positive airway pressure' (CPAP) is effective in relieving sleep apnea, and thus can help reduce the risk of its complications.

The scientists in this study didn't find a link between smoking and drinking alcohol and sleep apnea. Other studies, however, have found such links, providing further reasons to stop smoking and limit alcohol intake.

An important finding is that men over 50 and overweight people over 60 aren't any more likely to develop sleep apnea. In other words, women over 'a certain age' may also be at risk for sleep apnea - something their doctors should remember.