A prospective cohort study of physical activity in relation to lung cancer incidence among Black women

Abstract Background Black women have higher lung cancer incidence and mortality rates despite a lower smoking prevalence than White women. Physical activity may reduce lung cancer risk through several pathways, including the immune and inflammatory systems, as well as those with effects on sex hormones and metabolism. Methods We examined vigorous physical activity, walking for exercise, sitting watching television, and metabolic equivalents (METs) in relation to lung cancer risk among 38,432 participants in a prospective cohort of Black women. We used Cox proportional hazards models adjusted for covariates to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results In 1995–2017, 475 incident lung cancer cases accrued. Participants who engaged in ≥ 1 h/week of vigorous physical activity or expended the highest tertile of METs experienced a decreased risk of lung cancer (HR: 0.85, 95% CI: 0.65–1.10; 0.89, 0.68–1.18; respectively). An increased risk was observed for sitting watching television (≥1 h/week: 1.27, 0.72–2.21). In stratified models, an inverse association between walking for exercise and lung cancer risk was only present among former smokers (≥1 h/week: 0.71, 0.52–0.98), while inverse associations between vigorous physical activity (≥1 h/week: 0.45, 0.28–0.73) and METs (tertile 3: 0.54, 0.34–0.85) and lung cancer risk were present among smokers with ≥ 20 pack-years. Conclusion Physical activity may play a role in reducing lung cancer risk among Black women, particularly among smokers. Future studies should explore biologic mechanisms whereby physical activity may influence carcinogenesis and investigate the role of exercise interventions in reducing lung cancer risk among smokers. Highlights • Racial differences in lung cancer are not explained by smoking prevalence. • We found that walking for exercise reduced lung cancer risk among former smokers. • Vigorous exercise was inversely associated with cancer risk in a subset of smokers. • Physical activity may reduce lung cancer risk among smokers.   1 Introduction Lung cancer is the second most common cancer among Black women and accounts for the largest number of cancer deaths in this population nationwide [12] . Cigarette smoking is the primary risk factor for lung cancer. Although Black adults have lower prevalence of cigarette smoking and tend to smoke fewer cigarettes than White adults, lung cancer incidence and mortality are higher in Black smokers compared to White smokers 345 . Thus, other factors, including genetics 678 , metabolism [4] , and physical or social environment 91011 , are likely contributing to lung cancer disparities [2121314 . Black adults have a lower prevalence of physical activity than White adults 151617 and epidemiologic studies suggest that physical activity may be protective against lung cancer risk 18192021 . This association is most apparent among smokers 2223242526 . Recreational physical activity may reduce lung cancer risk among women by ≥ 10% [22242627] . In a recent meta-analysis of cohort studies, physical activity was associated with a 10% lower risk of lung cancer among women [28] , although the meta-analysis did not present results stratified by both sex and smoking status. To date, no studies have published data among Black women. Although there are biologic mechanisms to link physical activity with lung cancer risk, smoking is a strong confounder of the association. Several studies observed no relationship among never smokers [222930] , so it remains unclear whether physical activity is associated with lung cancer incidence. Thus, we examined the relation of physical activity to lung cancer among Black women overall and by smoking status using data from the Black Women’s Health Study cohort.