Daytime sleepiness in the obese: not as simple as obstructive sleep apnea.

OBJECTIVE: Excessive daytime sleepiness is a common symptom in obese patients, but what drives this condition is unclear. The objective was to look for clinical, anthropometric, biochemical, and polysomnographic predictors of excessive daytime sleepiness as measured by the Epworth Sleepiness Scale (ESS) in obese patients. RESEARCH METHODS AND PROCEDURES: The ESS questionnaire was completed by 1,055 consecutive patients presenting for obesity surgery. Those at high risk for obstructive sleep apnea (n = 331) had diagnostic overnight polysomnography preoperatively. All patients had preoperative clinical, hematologic, and biochemical measurements and completed multiple questionnaires.
RESULTS: There was no significant relationship between ESS score and any measure of diagnostic polysomnography factors, including total apnea hypopnea index. Subtle increases in ESS scores were reported in men, older patients, and those with type 2 diabetes. However, general demographic, anthropometric, and biochemical measures of the metabolic syndrome explained only 3% of ESS score variance, and inflammatory markers of C-reactive protein and total white cell count were not predictive. Poor Short Form-36 energy scores (b = -0.18, p < 0.001) and high Beck Depression Inventory scores were predictive of higher ESS scores (b = 0.15, p < 0.001) and, along with increasing age and male gender, explained 10% of variance. Symptoms related to disturbed nocturnal sleep explained 30% of variance.
CONCLUSION: In severely obese subjects, increased daytime sleepiness does not seem to be driven by obstructive sleep apnea, the degree of obesity, or anthropometric, metabolic, or inflammatory markers of the metabolic syndrome. It is, however, associated with poor energy, symptoms of depression, and symptoms of nocturnal sleep disturbance.