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Detailed findings and data

Active Smoking


People who smoke are twice as likely to have sleep apnoea when compared to those that do not smoke (pooled relative risk ratio 1.97, 95% confidence interval 1.02 to 3.82). Click here to see a forest plot of the findings – Figure A

However, data from one further study, which didn’t report numerical results, found smoking was not significantly associated with an increased risk of obstructive sleep apnoea (Stradling 1991).


Men were found to have a similar increased risk of sleep apnoea from smoking (1.5-fold increase) as women (1.5-fold increase) when compared to non-smokers; however, this analysis was only based on data from one study. Click here to see a forest plot of the findings – Figure B.

Number of cigarettes

One of the included studies looked at the effect of intensity of smoking based on the number of cigarettes smoked per day (Wetter 1994). This study found a dose−response relationship where the greatest risk of sleep apnoea was associated with smoking at least 40 cigarettes per day (relative risk ratio 8.38, 95% confidence interval 1.68 to 41.94). However, the impact of smoking on sleep apnoea in those consuming fewer cigarettes per day was inconsistent (less than 20 cigarettes per day: relative risk ratio 4.11, 95% confidence interval 1.41 to 11.99; 20-39 cigarettes per day: relative risk ratio 1.66, 95% confidence interval 0.60 to 4.58). 

Passive Smoking


One study (Kahn 1994) reported that maternal smoking during pregnancy approximately doubles the risk of the infant developing sleep apnoea (age range from 1 day to 29 weeks) (relative risk ratio 1.76, 95% confidence interval 1.17 to 2.64). 

Another study (Kukla 2005) reported that maternal smoking after birth significantly increases the risk of developing sleep apnoea in children aged 6-18 months (relative risk ratio 1.25, 95% confidence interval 1.06 to 1.47).  Click here to see a forest plot of the findings – Figure C.

The study of Kahn (1994) also reported an increase in sleep apnoea where both parents smoked during pregnancy when compared to only mothers smoking during pregnancy (p=0.007).