Researchers at the German Cancer Research Center (DKFZ; Heidelberg) examined the presence of phytoestrogens in blood samples of 1,140 women (aged 50 to 74 years) who had been diagnosed with postmenopausal breast cancer between 2002 and 2005. The patient’s vital status through the end of 2009 was ascertained using population registries, and deaths were verified by death certificates. Information on cancer recurrences and secondary tumors was verified by clinical records and by the attending physicians. The researchers examined the associations of postdiagnostic serum enterolactone--a biomarker for dietary lignans--with overall survival and distant disease-free survival over a mean observation time of six years.
The results showed that compared to the study subjects with the lowest enterolactone levels, the women with the highest blood levels of the biomarker had an approximately 40% lower mortality risk. When the researchers took into account the incidence of metastasis and secondary tumors, they obtained a similar result; women with the highest enterolactone levels also had a lower risk for unfavorable disease progression. However, the result was significant only for the group of tumors that have no receptor for estrogen, suggesting that enterolactone protects from cancer not only by its hormone-like effect, but also by promoting cell death and angiogenesis inhibition. The study was published ahead of print on the September 6, 2011, in the Journal of Clinical Oncology.
“We now have first clear evidence showing that lignans lower not only the risk of developing postmenopausal breast cancer, but also the mortality risk,” said lead author Prof. Jenny Chang-Claude, PhD. “By eating a diet that is rich in whole-meal products, seeds, and vegetables, which is considered to be health-promoting anyway, everybody can take in enough lignans. At the present time, we can only discourage people from taking any food supplements.”
Lignans are the most important type of phytoestrogens in Western diets, contained in seeds, particularly flaxseeds, as well as in wheat and vegetables. Other classes of phytoestrogens include isoflavones and coumestans. Lignans are capable of binding to estrogen receptors and interfering with the cancer-promoting effects of estrogen on breast tissue. In the bowel, lignans are turned into enterolactone, which is absorbed by the mucous tissue.
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