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Abstract & commentary
Synopsis: A 10% change in weight has a significant effect on the severity of sleep-disordered breathing.
Source: Peppard PE, et al. JAMA 2000;284:3015-3021.
This is a prospective, population-based study of 690 wisconsonites. Their mean age at entry was 46 years, and 56% were men. Body mass index (BMI, kg/m2) and apnea plus hypopnea index (AHI) were measured at baseline and four years later. At baseline and follow-up, AHI was correlated with BMI. At baseline, the 181 normal weight (BMI < 25 kg/m2) group had an AHI of 1.2 (± 2.4 events/h) The 241 overweight (25 < BMI < 30 kg/m2) subjects had an AHI of 2.6 (± 4.5 events/h). The 268 obese (BMI > 30) individuals had an AHI of 7.4 (± 13.1) events per hour. In follow-up, change in AHI was related to change in weight in a dose-response fashion. Thirty-nine subjects developed moderate-to-severe sleep apnea over the four years of study; this group had a mean weight gain of 3.9 (± 6.8) kg. Seventeen individuals who had moderate-to-severe sleep apnea at baseline had a reduction in AHI to below 15 events per hour at follow-up; this group lost 3.1 (± 6.2) kg. Each percentage change in weight (in either direction) was associated with an approximately 3% change in the AHI. Adjustment for menopausal status, physical activity, alcohol, or educational level did not materially affect the relationship between weight change and AHI. Cigarette smoking status was associated with change in AHI because smoking cessation was associated with weight gain in this study. However, change in cigarette packs smoked per week did not change the relationship between AHI and BMI.
Comment by Barbara a. Phillips, MD, MSPH
A history of recent weight gain is a common presenting symptom in patients with newly diagnosed sleep apnea. This study helps us to understand why. A 200-pound man who has an AHI of 12 would be predicted to have an AHI of about 15 or 16 if he gains 20 pounds. Although the exact AHI necessary to be clinically significant varies from person to person, most people with an AHI of 15 will be symptomatic. There is both good news and bad news here: the good news is that just a little more than 3 kg weight loss essentially cured some sleep apneics in this study. The bad news is that just a little more than 3 kg weight gain tipped some patients over into sleep apnea territory. And, in this study (as in my clinical practice, alas), there were far more people who gained weight than who lost it.
BMI has long been known to be associated with overall mortality. In healthy people who have never smoked, death from all causes rises progressively above a BMI of 23.5-24.9 in men and 22.0-23.4 in women.1 Much of the excess mortality associated with obesity is due to cardiovascular disease. Obstructive sleep apnea has been conclusively linked to hypertension and its sequelae,2-6 even controlling for obesity. Sleep-disordered breathing is part of the causal link between obesity and death.
One caveat to this important study is that the relationship between obesity and the risk of sleep apnea may not be so straightforward in non-Caucasian people. Several recent studies have demonstrated that ethnicity, particularly Asian and African-American race, are important risk factors for sleep apnea independent of obesity.7-12 (For a user-friendly website to calculate BMI, see: http://healthlink.mcw.edu/article/923520512.html.)
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