Effect of Flaxseed Consumption on Urinary Levels of Estrogen Metabolites in Postmenopausal Women
Effect of Flaxseed Consumption on Urinary Levels of Estrogen Metabolites in Postmenopausal Women
Year: 2010
Authors: Sturgeon, S.R.
Publication Name: Nutrition and Cancer
Publication Details: Volume 62; Number 2; Pages 175-180.
Abstract:
Flaxseed is a rich source of dietary lignans. It has been hypothesized that lignans may decrease breast cancer risk through modulation of endogenous hormone levels. The aim of this study was to determine the effect of flaxseed supplementation on urinary levels of estrogen metabolites that may be involved in the development of breast cancer. Forty-three postmenopausal women participated in this 12-wk preintervention and postintervention study. Participants consumed 7.5 g/day of ground flaxseed for 6 wk, followed by 15 g/day for an additional 6 wk. The mean urinary level of 16α hydroxyestrone (16α-OHE1) was higher at the end of 12 wk compared to baseline (change of 1.32 ug/day, P = 0.02). There was no significant change in 2-OHE1 excretion. The mean urinary level of the 2-OHE1/16α-OHE1 ratio was lower at the end of 12 wk compared to baseline (change of −1.1, P = 0.02).Mean urinary excretion of 2-methoxyestradiol was also lower at 12 wk than at baseline (P = 0.03). Based on the current paradigm of the effects of estrogen metabolism on breast cancer risk, the regimen of dietary flaxseed intake used in this study did not appear to favorably alter breast cancer risk through shifts in estrogen metabolism pathways in postmenopausal women. (Author's abstract)
It has been proposed that dietary lignans may modulate breast cancer risk through their effects on estrogen metabolism. The metabolism of estrone (E1) and estradiol (E2) occurs through three major competitive pathways: one involves 16α-hydroxylation to 16α-hyroxyestrone (16α-OHE1) and 16α-hydroxyestradiol (16α-OHE2); the second leads to 2-OHE1 and 2-OHE2; and a third leads to 4-OHE1 and 4-OHE2. A well-designed prospective cohort study observed an inverse association between diets rich in lignans and breast cancer risk. Flaxseed is a particularly rich source of lignans. The purpose of this study was to examine the effects of dietary flaxseed on urinary estrogen metabolites in a study that employed a laboratory approach to reliably measure a wide range of estrogen metabolites.This study showed a decline in the 2/16α-OHE1 excretion ratio with a 12-wk flaxseed intervention, corresponding with an increase in the urinary excretion of 16α-OHE1 from baseline to 12 wk. In this study, flaxseed intake was not correlated with a decline in the more optimal 2-hydroxestrogen metabolites as has been observed in other flaxseed intervention studies. Different estrogen metabolites have different biological activities, but it is still unclear what the optimal estrogen metabolism pattern is with respect to breast cancer. Findings from the Nurses Health Study reported no association between circulating levels of 2-OHE1 and breast cancer overall and an increase in risk for estrogen- and progesterone-negative tumors among women with higher 2-OHE1 levels. The findings of the present study do not suggest that dietary flaxseed intake has a favorable effect on the urinary estrogen metabolite profile based on the current paradigm of the effects of estrogen metabolism on breast cancer risk. However, these findings are not consistent with the majority of research in this area and thus further research is needed. (Editor's comments)
