Does smoking influence the physical activity and lung cancer relation? A systematic review and meta-analysis.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of observational studies
PubMed 27502335 · doi:10.1007/s10654-016-0186-y
What was done
A systematic review and meta-analysis of 25 observational studies (cohort and case-control) evaluating the association between physical activity (high versus low levels) and lung cancer risk, specifically analyzing whether smoking status or the degree of smoking adjustment influenced the association.
What was found
High versus low physical activity yielded an overall lung cancer summary relative risk (RR) of 0.79 (95% CI 0.72-0.87) across 25 studies, with RRs of 0.87 (95% CI 0.80-0.94) for cohort studies and 0.57 (95% CI 0.46-0.71) for case-control studies. In cohort analyses, physical activity was inversely related to lung cancer among former smokers (RR 0.68, 95% CI 0.51-0.90) and current smokers (RR 0.80, 95% CI 0.70-0.90), but showed no association among never smokers (RR 1.05, 95% CI 0.78-1.40, p interaction = 0.26). The degree of smoking adjustment did not modify the association (p interaction = 0.73).
Why it matters
Physical activity was inversely associated with lung cancer in smokers and former smokers but not in never smokers, highlighting that residual confounding by smoking may account for the observed benefits.
Limits
All included studies were observational. Total participant count was not reported in the abstract. The null association in never smokers may be constrained by lower statistical power, and residual confounding by smoking duration or intensity cannot be excluded.
Cited by
- supports Exercise reduces the risk of lung cancer even among individuals who actively smoke.