“The results of this meta-analysis indicate that overweight and obesity are protective factors against lung cancer, especially in current and former smokers,” conclude the authors of the report in International Journal of Cancer online July 29.
Dr. Yang Jiao, of the Medical College of Soochow University, Suzhou, People’s Republic of China, and colleagues point out that obesity is clearly a risk factor for colon, breast, renal and numerous other cancers, but a lower lung cancer risk has been observed in individuals with a higher BMI in some studies. However, other studies have found no association, or even the opposite.
They therefore conducted a meta-analysis of 31 relevant studies that included a total of 26,066 lung cancer cases among a pooled population of 79,915,395. Analysis of the data showed a statistically significant inverse association between BMI and risk of lung cancer.
The relative risk of lung cancer was 0.74 with a BMI of 25–29.9 (overweight) and 0.71 with a BMI of 30 or greater (obese), compared to normal weight (BMI of 18.5-24.9). Overall, for any excess weight (BMI of 25 or more), the relative risk was 0.79, the investigators found.
When stratified by smoking status, the relative risk for lung cancer associated with excess versus normal weight was 0.63 for current smokers, 0.73 among former smokers, and 0.83 in non-smokers, the team reports. For non-smokers, however, the inverse association was not significant when weight was classified as specifically overweight or obese.
When stratified by histologic subtype, the inverse association with body weight held for squamous cell carcinoma (RR = 0.68) and adenocarcinoma (RR=0.79), but not for small cell carcinoma (RR=0.99), according to the report.
The authors acknowledge that the biological mechanism underlying the protective effect of excess weight against lung cancer, particularly in smokers, is unclear. Still, they conclude, “The results suggest that attention to nutrition and maintenance of body weight could lower lung cancer incidence among smokers.”
Int J Cancer 2012.