Light, latitude and Epworth Sleepiness Scale in the European Sleep Apnea database - a daring proposal

<bold>Introduction:</bold> There are considerable differences in the daylight duration during summer versus winter and between northern and southern European regions. We hypothesised that duration and timing of daylight may affect the Epworth Sleepiness Scale (ESS) rating for daytime sleepiness in patients with obstructive sleep apnea (OSA). <bold>Methods:</bold> Patients from 41 sleep centres in 20 European countries across the latitudes 61° to 38° (n=35049, 30% females, age 53±19.9 years, body mass index [BMI] 31.8±6.8 kg/m2, apnea hypopnea index [AHI] 30±26 events/h) were analysed in the European Sleep Apnea Database (ESADA). We examined the association between day length across the year for different European geographical positions daytime sleepiness assessed by the ESS. <bold>Results:</bold> The ESS score varied between sleep centres (e.g., Crete 11.3±4.9, Dublin 11±5.6, Gothenburg 10.9±5.3, Warsaw 10.7±5.6, Hamburg 9.1±4.6, Lisbon 8.9±5.3, Brno 6.8±4.1, and Pavia 6.2±4.6), but was not different between geographical locations. Across the year, there was no correlation between the daylight length and ESS. The difference between apparent time and local time (solar zenith) has no impact on the ESS. BMI, AHI, diabetes, COPD, neurological disease and psychiatric disease were positively associated with ESS score (all P <0.01, respectively) whereas ESS slightly decreased with age (P<0.001). <bold>Conclusion:</bold> The length of daylight, the latitude, and the relative sunrise do not have a significant effect on subjective daytime sleepiness assessed by ESS in OSA patients.