Urinary and serum biomarkers of phytoestrogen exposure are not associated with breast cancer risk in the European Prospective into Cancer Norfolk study

Background

Phytoestrogens are a group of compounds found in plants that structurally resemble the hormone estradiol, and thus have the potential to act as estrogen agonists or antagonists. Their potential effects may alter the risk of breast cancer, but only a limited range of phytoestrogens has been examined in prospective cohort studies.

Methods

Serum and urine samples from 237 incident breast cancer cases and 952 controls (aged 45 to 75 years) in the European Prospective into Cancer (EPIC) Norfolk cohort were analyzed for seven phytoestrogens (daidzein, enterodiol, enterolactone, genistein, glycitein, o-desmethylangolensin, and equol) using liquid chromatography/mass spectrometry. Data on diet, demographics, anthropometrics, and medical history were collected upon recruitment. All models were adjusted for weight, fat and energy intake, family history of breast cancer, social class, analytical batch, and factors related to estrogen exposure.

Results

With a few exceptions, urinary or serum phytoestrogens were not associated with breast cancer risk in the EPIC Norfolk cohort. Breast cancer risk was marginally increased with higher levels of total urinary isoflavones (OR = 1.08 (95% CI = 1.00 to 1.16), P = 0.055); this association was stronger when restricted to premenopausal and perimenopausal women (OR = 1.30 (95% CI = 1.04 to 1.64), P = 0.022). Among the 105 women with estrogen receptor-positive tumours, the risk of breast cancer was increased with higher levels of urinary equol (OR = 1.07 (95% CI = 1.01 to 1.12), P = 0.013).

Conclusion

There was limited evidence of an association between phytoestrogens and breast cancer risk in the EPIC Norfolk cohort. Further study is required to determine whether the observations from the present study are replicated in other populations with similarly low relative intake of phytoestrogens.