Background:
In Hong Kong, only 18.9% of current smokers have tried smoking cessation services and most smokers (83.2%) quit without any assistance, which is less well studied. Physical activity may reduce tobacco cravings hence increase quitting. Little was known about behavioral influence on unassisted quitting in a general population. This study investigated the associations of physical activity with intention to quit and quitting in Chinese adult in Hong Kong, which is among the lowest smoking prevalence regions.

Methods:
In the Hong Kong Population Health Survey, 7084 land-based non-institutionalized subjects were interviewed face-to-face at baseline in 2003/04 and follow-up in 2006. Ethical approval was granted by a local institutional review board. Information on quit intention ('planned to quit in the next one month' versus 'none'), quitting ('ex-smokers' vs 'current smokers' in cross-sectional analysis, and 'new quitters' vs 'continuing smokers' in prospective analysis), and physical activity ('exercised any physical activity in the past 1 month' vs 'none') was collected. Logistic regression yielded ORs of quit intention and quitting for physical activity, adjusting for sex, 5-year age group, education, place of birth, income and co-habitant smoker(s). Among 1678 ever smokers at baseline, 323 were followed and were included in the prospective analysis.

Results:
Physical activity was non-significantly associated with an OR of 0.94 (95% CI: 0.68-1.30) for quit intention in current smokers at baseline. Physical activity was cross-sectionally and significantly associated with higher odds of ex-smoking (OR: 1.70, 95% CI: 1.36-2.14, p< 0.001) at baseline. Physical activity predicted higher but non-significant odds of quitting (1.67, 0.80-3.49, p=0.17) at follow-up.

Conclusions:
This was first study found that physical activity was associated with quitting in Chinese smokers. Prospective studies with better measurement of physical activity and larger sample size of smokers are needed to confirm the results.