Effect of flaxseed consumption on urinary estrogen metabolites in postmenopausal women

Flaxseed, the richest known source of plant lignans, has been shown to have chemoprotective effects in animal and cell studies. Some of its effects ma y be mediated through its influence on endogenous hormone production and me tabolism Two competing pathways in estrogen metabolism involve production o f the 2-hydroxylated and 16 alpha-hydroxylated metabolites. Because of the proposed differences in biological activities of these metabolites, the bal ance of the two pathways has been used as a biomarker for breast cancer ris k. We examined the effects of flaxseed consumption on urinary estrogen meta bolite excretion in postmenopausal women. Twenty-eight postmenopausal women were studied for three seven-week feeding periods in a randomized crossove r design. During the feeding periods, subjects consumed their usual diets p lus ground flaxseed (0, 5, or 10 g/day). Urinary excretion of the estrogen metabolites 2-hydroxyestrogen (2-OHEstrogen) and 16 alpha-hydroxyestrone (1 6 alpha-OHE1) as well as their ratio, 2/16 alpha-OHE1, was measured by enzy me immunoassay. Flaxseed supplementation significantly increased urinary 2- OHEstrogen excretion (p < 0.0005) and the urinary 2/16 alpha-OHE1 ratio (p < 0.05) in a linear, dose-response fashion. There were no significant diffe rences in urinary 16 alpha-OHE1 excretion. These results suggest that flaxs eed may have chemoprotective effects in postmenopausal women.