Isoflavones may reduce endometrial cancer risk
MedWire News: High intake of isoflavone-containing foods may be associated with a reduced risk for endometrial cancer in postmenopausal women, US study data show.
Previous studies have suggested that isoflavones, a class of nonsteroidal plant-based polyphenols found in legumes, and in especially high concentrations in soy, reduce the risk for endometrial cancer. However, inconsistent findings have been reported in the few epidemiologic studies conducted to date, note Nicholas Ollberding (University of Hawaii Cancer Center, Honolulu) and colleagues.
To investigate further, the researchers conducted a prospective analysis of 46,027 nonhysterectomized postmenopausal women who were recruited into the Multiethnic Cohort Study between 1993 and 1996 and provided detailed baseline information on diet and other endometrial cancer risk factors.
The team examined whether the consumption of legumes, soy, or tofu and the estimated intakes of total isoflavones or the specific isoflavones daidzein, genistein, or glycitein were associated with risk for endometrial cancer among the women.
During a median follow-up period of 13.6 years, 489 women were diagnosed with endometrial cancer.
As reported in the Journal of the National Cancer Institute, the risk for endometrial cancer was significantly inversely associated with total isoflavone intake. Indeed, the truncated (age 50-89 years) age-adjusted incidence rates were 107, 85, 98, 79, and 55 cases per 100,000 women per year in quintiles 1 (<1.59 mg/1000 kcal per day) through 5 (≥7.82 mg/1000 kcal per day), respectively.
Cox proportional hazards analysis showed that women in the highest quintile of total isoflavone intake had a significant 34% lower risk for endometrial cancer than those in the lowest quintile.
Similarly, women with the highest intakes of daidzein and genistein (≥3.54 and ≥3.40 mg/1000 kcal per day, respectively) had significant 36% and 34% lower risks for endometrial cancer than those with the lowest intakes (<0.70 and <0.69 mg/1000 kcal per day, respectively).
The associations remained significant after controlling for established endometrial cancer risk factors and for dietary factors related to total soy and isoflavone consumption.
By contrast, no statistically significant association with endometrial cancer risk was observed for increasing intake of legumes, soy, tofu, or glycitein.
Ollberding et al note that the lack of association between soy intake and cancer risk may be due to the fact that "a large proportion of isoflavones in the diets of older non-Asian women in the United States has been shown to come from food sources, such as soy proteins added to commercial baked goods, and through the consumption of foods with low to moderate isoflavone concentrations, such as coffee and orange juice, which are frequently consumed, rather than from traditional soy-based foods."
Using the partial population attributable risk percent, the researchers estimated that if all women in the study increased their total isoflavone intake to the level of those in the highest quintile, 26.7% of endometrial cancers may have been prevented.
"Although this counterfactual exposure scenario represents a rather large relative increase in intake from the current US average [0.7 mg/1000 kcal per day], a single cup (243 g) of soy milk provides approximately 23 mg of total isoflavones," Ollberding and co-authors remark.
"Should further research support the advisability of increasing isoflavone intake to this level among all US women, based on these estimates, the implementation of such a recommendation could have an appreciable impact on the 43,470 cancers of the uterine corpus diagnosed annually," they conclude.
By Laura Dean