Soy Intake Linked to Lower Risk for Colorectal Cancer in Postmenopausal Women

Laurie Barclay, MD

January 29, 2009

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January 29, 2009 — Consumption of soy foods is associated with a lower risk for colorectal cancer in postmenopausal women, according to the results of a prospective study reported in the February issue of the American Journal of Clinical Nutrition.

"Soy and some of its constituents, such as isoflavones, have been shown to have cancer-inhibitory activities in experimental studies," write Gong Yang, from Vanderbilt University School of Medicine in Nashville, Tennessee, and colleagues. "Data from epidemiologic studies linking usual soy food intake with colorectal cancer are limited and inconsistent."

The goal of this study was to evaluate whether intake of soy food is associated with a risk for colorectal cancer. The study cohort consisted of 68,412 women aged 40 to 70 years and without cancer or diabetes at enrollment. In-person interviews using a validated food-frequency questionnaire evaluated usual soy food intake at baseline (1997-2000) and during the first follow-up (2000-2002). To minimize lifestyle changes related to preclinical disease, the first year of observation was excluded.

There were 321 incident cases of colorectal cancer identified during a mean follow-up of 6.4 years. Total soy food intake was inversely associated with colorectal cancer risk, after adjusting for potentially confounding variables. For each 5-g/day increment in dietary intake of soy as measured by dry weight (equivalent to approximately 1 oz [28.35 g] tofu/day), there was an 8% reduction in risk (95% confidence interval [CI), 3% - 14%).

Compared with women in the lowest tertile of soy intake, those in the highest tertile had a multivariate relative risk (RR) of 0.67 (95% CI, 0.49 - 0.90; P for trend = .008). This inverse association was primarily confined to postmenopausal women. Findings were similar for soy protein and isoflavone intakes.

Limitations of this study include possible measurement error in assessing soy food intake.

"This prospective study suggests that consumption of soy foods may reduce the risk of colorectal cancer in postmenopausal women," the study authors write. "Given the fact that colorectal cancer is one of the most common cancers worldwide and that soy can be readily incorporated into most diets, our findings have important public health implications in the prevention of this common malignancy."

The US Public Health Service and the National Institutes of Health intramural program supported this study. The study authors have disclosed no relevant financial disclosures.

Am J Clin Nutr. 2009;89:577-583.

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