Risk Factors for Sleep Apnea

Summarized by Robert W. Griffith, MD
August 29, 2003

Introduction

There haven't been any good studies that demonstrate the incidence of sleep-disordered breathing, or sleep apnea. The condition doesn't always receive the prominence it deserves; it's associated with daytime sleepiness, as well as an increased risk of hypertension and cardiovascular disease. So the recent report in JAMA on the occurrence of sleep apnea and its risk factors represents an important contribution to the literature.

Method

The purpose of the Cleveland Family Study, which represents a relatively young urban population living in Cleveland, Ohio, USA, is to determine the incidence of obstructive sleep apnea over a 5-year period. Out of the entire population, 1149 individuals aged 18 or over completed a baseline sleep study; after exclusion of those with at least one family member with confirmed sleep apnea, or themselves having an AHI (Apnea-Hypopnea Index)¹ of 5 or above, there were 536 participants remaining in the study. These were followed for 5 years, and 286 of them completed a second sleep examination, providing the study population for analysis.

Wide-ranging information on each subject was gathered, along with a physical examination, assessment of the presence of tonsillar hypertrophy or upper airway obstruction, blood pressure, cholesterol levels, and overnight in-home sleep monitoring.

Results

At baseline, the 286 subjects were 72% female, 21% black, 16% had cardiovascular disease and/or diabetes, and 42% snored. Their mean BMI was 27.6 and their mean age was 36.8 years. Their characteristics were similar to those of eligible subjects who didn't complete the second sleep examination. There were no differences at baseline between subjects from sleep-apnea families and those from control families.

At the second visit, 181 participants (63%) 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 9.9, 6% an AHI between 10 and 15 (mild to moderately severe sleep apnea), and 10% had an AHI over 15 (moderately severe sleep apnea).

Logistic regression analyses showed that AHI was significantly and independently associated with increasing age, increasing BMI, male sex, increasing waist/hip ratio, and increasing serum cholesterol level. The incidence of sleep apnea was not influenced by race, large tonsils, smoking, alcohol use, or family history of the condition.

The association of male gender with the development of sleep apnea disappeared after the age of 50, and the influence of BMI disappeared after age 60 years.

Comment

In the discussion of their results, the investigators point out that, in a separate study, around 2.5% of sleep apnea subjects with an AHI over 15 were found to 'improve' considerably, having a second AHI level of 5 or below. They therefore adjust the incidence of moderately severe sleep apnea in this study from 10% down to 7.5%.

Nevertheless, the 5-year incidence of sleep apnea in this relatively young urban population is disturbing. The increased risk of cardiovascular disease and cognitive impairment in subjects with a raised AHI is highly relevant. Fortunately, continuous positive airway pressure (CPAP) treatment offers the ability to reverse AHI levels, and thereby reduce the risk of recognized complications of the disorder.

The absence of an association between smoking or alcohol use with sleep apnea in this study is surprising, as these have been regarded as risk factors in the past. More important is the recognition that after age 50 or 60 the typical features of the sleep apnea patient - an obese, hypertensive male - tend to ebb, so that the possibility of its existence in, say, a frail older woman should not be neglected.

Source

• Incidence of sleep-disordered breathing in an urban adult population. The relative importance of risk factors in the development of sleep-disordered breathing. PV. Tishler, EK. Larkin, MD. Schluchter,  et al., JAMA, 2003, vol. 289, pp. 2230--2237

Footnotes
1. The Apnea-Hypopnea Index is the total number of episodes of either apnea or hypopnea divided by the number of hours of sleep.

Related Links
Cyberounds: Sleep Apnea
Disease Digests: Sleep Apnea
Sleep Apnea -- A New Approach?

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