Background: Previous studies have investigated the relationship between obstructive sleep apnea syndrome (OSA) and smoking, showing a higher smoking prevalence in OSA patients. On the other hand, non-OSA-related disorders are still to be addressed. This study aimed to assess possible relations between smoking and OSA-related symptoms, sleep study findings and co-morbidities. Non-OSA-related sleep disorders were also evaluated.

Methods: A cross-sectional study that included all adult patients visiting a sleep clinic who provided information about their smoking history. Sleep-related characteristics, derived from questionnaires and sleep studies, were compared between current, former and never smokers, while current and former smokers were grouped into a group of ever smokers.

Results:  4347 patients (1498 never, 1480 former and 1369 current smokers) were included. Ever smokers were more obese (BMI, p=0.002), with increased prevalence of metabolic and cardiovascular co-morbidities compared to never smokers. They  presented significantly higher apnea?hypopnea index (AHI) compared to never smokers (34.4 ±24.6 vs.31.7 ± 23.6 events/h, p < 0.001)  with more severe OSA (50.3% vs. 46.9%). Epworth sleepiness scale (ESS) (p = 0.13) did not differ between groups. Ever smokers, compared to never smokers, presented more frequent episodes of sleep talking (30.8% vs. 26.6%, p = 0.004), abnormal movements (31.1% vs. 27.7%, p = 0.021), restless sleep (59.1% vs. 51.6%, p < 0.001) and leg movements (p = 0.002) during sleep. Those were more evident in current smokers and correlated  with increasing AHI.

Conclusion: Our findings suggest the existence of a smoking-induced disturbed  sleep pattern.