Physical activity and risk of lung cancer

Background Physical activity has been proposed to decrease lung cancer risk ; however, few data are available. Further, no studies have examined specif ic kinds and intensities of activities. Methods We conducted a prospective cohort study among 13 905 male Harvard U niversity alumni (mean age, 58.3 years), free of cancer. Men reported their walking, stair climbing and participation in sports or recreation on basel ine questionnaires in 1977, and the occurrence of lung cancer on follow-up questionnaires in 1988 and 1993. Death certificates were obtained for deced ents through 1992 to determine lung cancers not previously reported. Results During follow-up, 245 men developed lung cancer. Adjusting for age, cigarette smoking, and body mass index, the relative risks of lung cancer associated with <4200, 4200-8399, 8400-12 599 and greater than or equal to 12 600 kJ/week of estimated energy expenditure at baseline were 1.00 (refer ent), 0.87 (95% CI : 0.64-1.18), 0.76 (95% CI : 0.52-1.11), and 0.61 (95% C I : 0.41-0.89), respectively; P trend = 0.0008. Similar trends were observe d among non-smokers or former smokers in 1977 (82.7% of men) as well as amo ng those who smoked >20 cigarettes a day in 1977 (8.0%), although the findi ngs in the latter group were not statistically significant, possibly due to the small number. Walking, climbing stairs and participating in activities of at least moderate intensity (greater than or equal to 4.5 MET, or multi ples of resting metabolic rate) were each inversely associated with lung ca ncer risk, independent of the other activity components. However, light int ensity activities (<4.5 MET) did not predict lung cancer risk. Conclusions These data indicate that physical activity may be associated wi th lower risk of lung cancer among men. An energy expenditure of 12 600 kJ/ week, achievable by perhaps 6-8 hours of at least moderate intensity physic al activity, may significantly lower risk. Further studies are required to confirm these observations.