Dietary Estrogens Influence Urinary Lignan Excretion in a Dose-Dependent Manner in Post-Menopausal Women

Abstract

Dietary estrogens, such as lignans, are similar in structure to endogenous sex steroid hormones and may act in vivo to alter hormone metabolism and subsequent cancer risk. The objective of this study was to examine the effect of dietary intake of a lignan-rich plant food (flaxseed) on urinary lignan excretion in post-menopausal women. This randomized, crossover trial consisted of three 7-week feeding periods during which 31 healthy post-menopausal women, aged 52-82, recruited from the Monastery of the Sisters of the Order of St. Benedict in St. Joseph, MN consumed their habitual diets plus 0, 5 or 10 grams of ground flaxseed. Urine samples collected for 2 consecutive days during the last week of each feeding period were analyzed for lignan content (enterodiol, enterolactone, matairesinol) by isotope dilution gas chromatography/mass spectrometry. Compared to the 0g flaxseed diet, consuming 5 or 10g of flaxseed increased excretion of enterodiol by 3.73 (2.71-5.13) pmol/mg creatinine (95% confidence interval [CI]), p=0.0001 and 8.71 (6.32-11.99) pmol/mg creatinine (95% CI), p=0.0001, respectively, and increased excretion of enterolactone by 7.15 (5.48-9.12) pmol/mg creatinine (95% CI), p=0.0001 and 16.18 (12.41 -21.09) pmol/mg creatinine (95% CI), p=0.0001, respectively. Excretion of matairesinol was not significantly altered with flaxseed feeding. Consuming flax, a significant source of dietary estrogens, in addition to their habitual diets increased excretion of enterodiol and enterolactone, but not matairesinoi, in a dose-dependent manner in this group of post-menopausal women. Urinary excretion of lignan metabolites is a dose-dependent biomarker of flaxseed intake within the context of a semi-controlled diet.