WESTPORT, CT (Reuters Health) – Evidence from Singapore indicates that intake of dietary soy food and a longer menopausal cycle protect against lung cancer in nonsmoking women, according to a report in the January 20th issue of the International Journal of Cancer.
Dr. Adeline Seow, of the National University of Singapore, and colleagues note that Chinese women have a high incidence of lung cancer despite low smoking rates. In a hospital-based study of Singapore Chinese women, the investigators collected demographic and dietary data on 303 cases of lung cancer and 765 age-matched controls. Of these, 176 cases and 663 controls were lifetime nonsmokers.
Among smokers, intake of total, cruciferous and non-cruciferous vegetables was inversely associated with lung cancer. Though the risk was lower among smokers in the highest tertile of fruit intake, it was not statistically significant.
The investigators observed a significantly reduced lung cancer risk among nonsmokers, but not smokers, with higher intakes of soy foods. Nonsmokers in the upper tertile of soy isoflavonoid intake had a relative risk of 0.56 compared with those in the lowest tertile (p < 0.01).
There was a significant association between fruit intake and a reduced risk of lung cancer among nonsmokers. After controlling for fruit intake, soy intake independently predicted risk of lung cancer.
"Reproductive effects were also primarily confined to lifetime nonsmokers, among whom having three or more livebirths (adjusted odds ratio 0.65) and a menstrual cycle length of more than 30 days (adjusted odds ratio 0.46) accorded a significantly reduced risk of lung cancer," the team reports.
Stepwise regression showed that among nonsmokers, soy intake and menstrual cycle length were the independent dietary and reproductive predictors of lung cancer risk.
"These findings are consistent with other evidence suggesting an involvement of estrogen-related pathways in lung cancer among nonsmoking women," Dr. Seow and colleagues conclude.