Last Updated: 2009-11-06 16:16:41 -0400 (Reuters Health)

NEW YORK (Reuters Health) - Low body mass index (BMI) is strongly associated with an increased risk of lung cancer among current smokers, researchers report in the November issue of the International Journal of Cancer.

"Our study was based on a nationally representative prospective cohort study of (about) 220,000 men in China, where mean BMI is relatively low and lung cancer mortality is high despite (the fact) that few have smoked cigarettes persistently over the last few decades," lead investigator Dr. Ling Yang from the University of Oxford, UK, told Reuters Health. "It has confirmed the fundamental importance of smoking as a major cause of lung cancer."

The researchers' findings are from a 15-year prospective cohort study including 217,180 Chinese men between the ages of 40 and 79 years at baseline in 1990 to 1991, with no prior history of cancer. Of these, 67% were current smokers and 27% were lifelong non-smokers.

Their mean BMI was 21.7 kg/m2. Overall, 9.2% of men were underweight (<18.5 kg/m2) and 11.2% were either overweight (25 to 30 kg/m2) or obese (>30 kg/m2).

A strong inverse association was observed between the prevalence of smoking and BMI. However, no apparent association was found between the amount smoked and BMI among current smokers.

A total of 2145 lung cancer deaths were reported over 15 years of follow-up. The overall adjusted hazard ratio for lung cancer among current smokers was 1.77. Urban men had a higher risk than rural men (HRs 2.28 versus 1.57).

A strong inverse association was observed between BMI and lung cancer mortality after adjusting for potential confounders and excluding the first 3 years of follow-up (p < 0.0001). The relationship appeared to be modified by smoking status, with the effect confined mainly to current smokers.

"Although the risk ratio of lung cancer for smokers in China is currently much lower than that typically seen in Western populations, the absolute risk of the disease associated with smoking is not, given the high background rate of the disease in the population, and it is likely to increase substantially in the future owing to the delayed effects from the recent large increase in cigarette consumption in China," Dr. Yang said. "Tobacco control is, therefore, the major and long-term strategy on preventing and controlling for the risk of lung cancer in China."

Int J Cancer 2009;125:2136-2143.