A meta-analysis of case-control and cohort studies that included 11,346 cases and 140,177 controls found no association between enterolactone, matairesinol, secoisolariciresinol, or total lignans and prostate cancer.7 A systematic review came to a similar conclusion: most epidemiologic studies found no association between prostate cancer risk and dietary intake of flaxseed lignans or serum levels of enterolactone.8
Clinical studies, however, found that dietary flaxseed affected tumor markers.8 In a study of men with prostatic intraepithelial neoplasia, 30 g per day of flaxseed for 6 months decreased serum total prostate specific antigen (PSA) and the proliferation rate of benign epithelial cells. Another study among men with prostate cancer with a planned prostatectomy who received 30 g of flaxseed per day for about 34 days demonstrated decreased total testosterone and free androgen levels, decreased tumor proliferation index among men with a Gleason score of 6 or less, and increased tumor apoptotic scores. A similar study also demonstrated lower tumor proliferation rates with 30 g per day of flaxseed consumed by men awaiting prostatectomy.
Another study of men with localized prostate cancer showed that 30 g per day of flaxseed for about 30 days increased urinary concentrations of flaxseed lignans, and these concentrations were significantly associated with Ki–67 tumor expression.9
Epidemiologic data of flaxseed dietary intake and high enterolactone serum concentrations — as well as in-human biomarker studies conducted in a randomized controlled design — suggest that flaxseed consumption may reduce the risk of breast cancer. The data are less clear for prostate cancer, but biomarker studies suggest that consumption of 30 g per day of flaxseed can reduce PSA levels and tumor proliferation rate. Larger studies are needed to validate the effect of flaxseed consumption on cancer prevention or treatment.
- Toure A, Xeuming X. Flaxseed lignans: source, biosynthesis, metabolism, antioxidant activity, bio-active components, and health benefits. Compr Rev Food Sci Food Safety. 2010;9:261-9.
- Zaineddin AK, Vrieling A, Buck K, et al. Serum enterolactone and postmenopausal breast cancer risk by estrogen, progesterone and herceptin 2 receptor status. Int J Cancer. 2011;130:1401-10. doi: 10.1002/ijc.26157
- Seibold P, Vrieling A, Johnson TS, et al. Enterolactone concentrations and prognosis after postmenopausal breast cancer: assessment of effect modification and meta-analysis. Int J Cancer. 2014;135:923-33. doi: 10.1002/ijc.28729
- Lowcock EC, Cotterchio M, Boucher BA. Consumption of flaxseed, a rich source of lignans, is associated with reduced breast cancer risk. Cancer Causes Control. 2013;24:813-6. doi: 10.1007/s10552-013-0155-7
- Thompson LU, Chen JM, Li T, Strasser-Weippl K, Goss PE. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res. 2005;11:3828-35.
- McCann SE, Edge SB, Hicks DG, et al. A pilot study comparing the effect of flaxseed, aromatase inhibitor, and the combination on breast tumor biomarkers. Nutr Cancer. 2014;66:566-75. doi: 10.1080/01635581.2014.894097
- Zhang Q, Feng H, Qluwakemi B, et al. Phytoestrogens and risk of prostate cancer: an updated meta-analysis of epidemiologic studies. Int J Food Sci Nutr. 2017;68:28-42. doi: 10.1080/09637486.2016.1216525
- Saarinen NM, Tuominen J, Pylkkänen L, Santti R. Assessment of information to substantiate a health claim on the prevention of prostate cancer by lignans. Nutrients. 2010;2:99-115. doi: 10.3390/nu2020099
- Azrad M, Vollmer RT, Madden J, et al. Flaxseed-derived enterolactone is inversely associated with tumor cell proliferation in men with localized prostate cancer. J Med Food. 2013;16:357-60. doi: 10.1089/jmf.2012.0159