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Often, as now, I am surprised to learn that what seems like a basic, important link of knowledge has been so long missing from the body of research. Weight loss, so often recommended to OSA patients as a therapeutic measure, has apparently never before been studied in OSA patients under treatment!I suspect this results from a tendency to view the relationship of obesity to OSA as a one-direction cause and effect. That is, the OSA patient becomes obese the same way that anybody else does—basically unknown, but with an unspoken assumption of underlying sloth and gluttony—and the sleep apnea itself doesn’t alter this process. However, among the articles on this website we have already seen evidence of hormonal changes resulting from OSA which can predispose to weight gain (see Article #34: Metabolic Aspect of Sleep Apnea). Moreover, it makes common sense that a person lacking energy and time to cope with essential daily tasks will find it difficult to exercise regularly or follow a diet program.
There are anecdotal reports that some patients lose weight rapidly after starting treatment for OSA with CPAP, but to the authors’ knowledge no systematic studies to date.
The database for this study consisted of records of patients evaluated at the Scripps Clinic Sleep Disorders Center during three months in 1994. The study was limited to those patients who were overweight, as defined by a Body Mass Index or BMI (see Glossary) between 25 and 30, or obese, defined by a BMI over 30. The authors eliminated patients with chronic illnesses (such as cancer) likely to cause weight loss, or on medications likely to cause weight loss.
This left 46 patients who met the study criteria. CPAP compliance was assessed by self-report, and considered adequate if patients reported using CPAP more than 4 hours per night on a regular basis. Weights, obtained on initial clinical evaluation and at follow up about six months (=/-3 months) later, were available for 35 of the 46 patients. Three additional patients were excluded because of subsequent stimulant drug use (methylphenidate/Ritalin or fluoxetine/Prozac). Of the remaining 32 patients (22 men and 10 women, average age 57, respiratory disturbance index 45), 21 (66%) were considered compliant and 11 (34%) non-compliant. Non-compliant patients stopped CPAP within the first two weeks; no patients who were initially compliant later stopped complying.
The authors decided that weight loss had to exceed 4.5 kg (10 pounds) to be significant, and they used that as a cutoff value to identify patients who had lost significant weight since starting CPAP. Among the CPAP compliant patients, 9 of 21 (43%) lost this much, versus none of the 11 non-compliant patients, a statistically significant difference.
The authors suggested four mechanisms by which CPAP might help OSA patients lose weight, of which they seemed to favor the first two. (1) Decreased daytime sleepiness could result in more daytime activity. (2) Patients more compliant with CPAP might also be more motivated to pursue weight loss measures. (3) CPAP might alter metabolism. (4) CPAP might alter hormonal function. They noted the need for longer-term studies to evaluate whether CPAP-related weight loss is well maintained.
Perhaps the more important question is, Why do less than half of CPAP compliant patients lose significant amounts of weight? The authors did not attempt to correlate this weight loss with any other indications of the effectiveness of the treatment, such as normalization of the Respiratory Distress Index or relief of daytime sleepiness, but I would wonder whether those compliant patients who failed to lose weightalso failed to receive optimal treatment, whether due to mismatch of CPAP pressures and needs or emergence of other sleep-disruptive factors such as Periodic Leg Movements of Sleep. On the other hand, it may merely represent a failure of the sleep medicine community to refer the patient into a weight management program at a time of opportunity. Or perhaps the problem is a character defect of sloth and gluttony after all?!
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