Phytoestrogens Inhibit Lung Cancer

Dietary intake of phytotestrogens reduces the risk of lung cancer, according to a study published in the Journal of the American Medical Association (JAMA), 294:1493-1504, 2005).

In the eight-year study, researchers used food frequency questionnaires to collect demographic information and assess dietary intake of 12 individual phytoestrogens in subjects from an ongoing case-control study of 1,674 patients with lung cancer and 1,735 matched healthy controls. Risk of lung cancer was estimated using unconditional, multivariable logistic regression analyses stratified by sex and smoking status, and adjusted for established and putative lung cancer risk factors. With each increasing quartile of phytoestrogen intake, risk of lung cancer dropped. Subjects with the highest intake of total phytosterols, isoflavones, lignans and phytoestrogens showed reductions in risk of lung cancer ranging from 21 percent for phytosterols to 46 percent for total phytoestrogens derived solely from food sources.

The researchers also discovered gender-specific effects. For men, statistically significant trends for the inverse association between phytoestrogen intake and lung cancer were noted for each phytoestrogen group, with protective effects for the highest quartile of intake ranging from 24 percent for phytosterols to 44 percent for isoflavones; in women, significant trends were only present for intake of total phytoestrogens derived solely from food sources, with a 34-percent protective effect for the highest quartile of intake. High phytoestrogen intake had an apparently beneficial effect in both individuals with no history of smoking as well as current smokers, but the beneficial effects were less in former smokers. In women taking hormone therapy and consuming phytoestrogens, statistically significant effects were evident between the combination of hormone therapy and phytoestrogen intake; specifically, high intake of the lignans enterolactone and enterodiol and use of hormone therapy were associated with a 50-percent reduction in risk of lung cancer.

The researchers concluded while there are limitations and concerns regarding case-control studies of diet and cancer, these data provide further support for the limited but growing epidemiologic evidence that phytoestrogens are associated with a decrease in risk of lung cancer, and noted confirmation of these findings is still required in large-scale, hypothesis-driven, prospective studies.