STUDY:

JOURNAL: Am J Clin Nutr. 2004;79:183-184, 282-288

AUTHORS: Lital Keinan-Boker

ABSTRACT: High intake of isoflavones does not increase risk of breast cancer, according to the results of a prospective, population cohort study published in the February issue of the American Journal of Clinical Nutrition.

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COMMENTARY: "Soy foods are rich in isoflavones, and Asian populations habitually consume large amounts of soy foods. Ecologic observations suggest that the intake of soy foods plays a role in the prevention of breast cancer," write Lital Keinan-Boker, from the University Medical Center in Utrecht, the Netherlands, and colleagues. "Several studies, but not all, showed protective effects of soy in Asian populations. No such associations were suggested for Western subjects."

This study followed 15,555 Dutch women, aged 49 to 70 years, enrolled from 1993 to 1997 in the European Prospective Investigation into Cancer and Nutrition (EPIC). This population has a habitually low phytoestrogen intake.

Using a validated food-frequency questionnaire, the investigators determined habitual dietary intake in the preceding year, and they estimated dietary content of isoflavones and lignans based on a literature search, food-composition tables, and expert opinion. The Comprehensive Cancer Center Middle Netherlands identified 280 newly diagnosed breast cancer cases during follow-up through Jan. 1, 2001.

Median daily intake of isoflavones was 0.4 mg/day (interquartile range [IR], 0.3 - 0.5 mg/day) and of lignans was 0.7 mg/day (IR, 0.5 - 0.8 mg/day). Compared with the lowest intake quartiles, hazard ratios for the highest intake quartiles were 1.0 (95% confidence interval [CI], 0.7 - 1.5) for isoflavones and 0.7 (95% confidence interval, 0.5 to 1.1) for lignans.

"The results of the present study, which focused on Western women whose habitual diet is low in phytoestrogens, showed no protective effects of isoflavones or lignans against breast cancer," the authors write. "Consumption of vegetables, fruit, grain products, and nuts accounted for most of the lignan intake.... Because these food groups are frequently consumed in Western diets, it is reasonable to assume that the intake of lignans is stable over the course of a lifetime and occurs at younger ages also, which is important if lignan intake is relevant only at younger ages, as has been suggested for isoflavones."