Dietary Phytoestrogens and Lung Cancer Risk

By Louis Kuritzky, MD Dr. Kuritzky is Clinical Assistant Professor, University of Florida, Gainesville. Dr. Kuritzky is a consultant for GlaxoSmithKline and is on the speaker's bureau of GlaxoSmithKline, 3M, Wyeth-Ayerst, Pfizer, Novartis, Bristol-Myers Squibb, AstraZeneca, Jones Pharma, and Boehringer Ingelheim.

Source: Schabath MB, et al. Dietary phytoestrogens and lung cancer risk. JAMA 2005;294:1493-1504.

Lung cancer remains the leading cause of cancer death in the United States, and has recently surpassed even heart disease as a cause of mortality among men who smoke. Past epidemiologic data suggested that dietary constituents such as vitamin A and beta-carotene might be important modulators of lung cancer risk but, unfortunately, interventional trials did not support the optimism generated by observational data.

Phytoestrogens are compounds in the diet that have weak estrogen-like activity. The three main phytoestrogen classes are isoflavones, lignans, and cumestrans. Epidemiologic data have shown that in populations with a low incidence of lung cancer, plasma levels of isoflavones and lignans are high.

Schabath et al studied the relationship between intake of phytoestrogens and lung cancer risk in a prospective case-control study (n = 3,409). Data were obtained by personal interviews querying food intake over a nine-year period of observation.

Among the study population, there was an equal frequency of never-smoking history: approximately 16%. This also helps to remind us that as many as one out of six lung cancer cases occur in non-smokers.

There was a linear inverse relationship between dietary phytoestrogens and lung cancer which proved to be statistically significant, but was primarily driven by data accrued in men. Those individuals in the highest intake of dietary phytoestrogens enjoyed a 46% relative risk reduction for lung cancer compared to controls. These data are consonant with previous information suggesting that estrogenic hormone therapy is protective for lung cancer in women. In nonsmokers, trends towards benefit were more prominent than in smokers or former smokers, but the small numbers of study subjects precludes definitive conclusions.