Flaxseed, Lignans and Sex Hormones. Flaxseed in Human Nutrition.
Flaxseed, Lignans and Sex Hormones. Flaxseed in Human Nutrition.
Year: 1995
Authors: M S Kurzer, J L Slavin, H Aldercreutz.
Publication Name: AOCS Press, Champaign, Ill.
Publication Details: 137;143.
Abstract:
In this review chapter, the authors present evidence which links flaxseed lignan consumption with alterations in sex hormone metabolism. flaxseed lignans are found as secoisolariciresinol diglycoside (SDG) and marairesinol (MS). In mammals, the lignans enterolactone (EL) and enterodial (ED) are formed from MS and SDG, respectively, by the action of intestinal bacteria. EL may also be produced by oxidation of ED. In breast cancer patients and individuals at high risk of breast and colon cancer, the urinary excretion of mammalian lignans is significantly lower than in individuals who consume vegetarian diets or those at lower risk of developing cancer. A Western style diet elevates plasma levels of sex hormones and decreases levels of sex hormone binding globulin (SHBG) thus increasing the exposure of breast and other tissues to these hormones. Lignan structure is very similar to anti-carcinogenic compounds such as tamoxifen which has weak estrogenic/anti-estrogenic properties and suggests that lignan consumption may alter hormonal status. Mammalian lignans are able to bind to estrogen receptors and thus have weak estrogenic and antiestrogenic properties. The reported antiestrogenic effects of flaxseed lignans include growth inhibition of estrogen-sensitive breast cancer cell lines; inhibition of estradiol-stimulated RNA synthesis in animal uterus; competition with estradiol for uterine nuclear estrogen-binding sites in rats and inhibition of the aromatase enzyme involved in testosterone and estrogen synthesis. Only two controlled experiments have evaluated the effects of flaxseed on sex hormones in humans. Following flaxseed feeding, the urinary and fecal excretion of EL and ED increased in a group of premenopausal women. The urinary excretion of EL in both pre- and post-menopausal women has been shown to correlate positively with plasma SHBG and negatively with plasma levels of free estradiol and testosterone. Lignans may thus protect against breast cancer and other hormone-related cancers by stimulating SHBG synthesis in the liver. SHBG binds estrogen and decreases the levels of circulating free estrogen. In premenopausal women, a lengthened menstrual cycle (increased luteal phase length) that was related to a reduction in estradiol has been observed following flaxseed feeding. Increased luteal phase length was associated with an increased progesterone/estradiol ratio and fewer anovulatory cycles reflected a decreased tendency toward ovarian dysfunction. The authors indicate that available research suggests that the anti-estrogenic effects of lignans may contribute to the anticarcinogenic properties of flaxseed diets. Initial studies in pre-menopausal women have shown that flaxseed feeding influences sex hormone metabolism. Future controlled studies in this area appear to be warranted.
