Moderate intake of dietary isoflavone lowers lung cancer risk in nonsmoking women

A moderate increase in the consumption of foods rich in isoflavone can help reduce the risk of lung cancer in women with no smoking history, suggests a study.

The authors carried out a nested case-control study within a population-based prospective cohort study of women. They identified 478 incident lung cancer patients and their individually matched controls among never-smoking women after a mean follow-up of 15.6 years.

Repeated dietary surveys and urinary biomarkers were used to assess habitual intake of and internal exposure to phytoestrogens, respectively. The authors estimated odds ratios (ORs) and 95 percent confidence intervals (CIs) in conditional logistic regression models.

Moderate intakes of isoflavone-rich foods showed an inverse association with lung cancer risk in never-smoking women after adjusting for potential confounders (second vs lowest quartile of intake: OR, 0.52, 95 percent CI, 0.35‒0.76).

A further increase in consumption did not result in additional benefits (third quartile: OR, 0.53, 95 percent CI, 0.36‒0.78; fourth quartile: OR, 0.47, 95 percent CI, 0.31‒0.72; p<0.001 overall and p=0.006 for nonlinearity).

When assessing exposure to isoflavones by urinary biomarkers, the authors observed a similar association. The corresponding ORs for the second, third, and fourth quartiles compared with the lowest quartile of urinary isoflavone excretion were 0.57 (95 percent CI, 0.39‒0.83), 0.64 (95 percent CI, 0.44‒0.92), and 0.60 (95 percent CI, 0.41‒0.86).

The inverse association reached a plateau beyond the second quartile (p=0.04 overall and p=0.15 for nonlinearity). Additionally, no association was found between urinary excretion of gut microbiota-derived metabolites of lignans and risk of lung cancer.