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Dietary supplement use by patients with cancer has increased significantly over the past 2 decades despite insufficient evidence of safety and effectiveness. Finding reliable sources of information about dietary supplements can be daunting. Patients typically rely on family, friends, and the Internet, often receiving misleading information.

The ASCO Post’s Integrative Oncology series is intended to facilitate the availability of evidence-based information on complementary therapies commonly used by patients with cancer. We chose flaxseed for this issue because of its increasing use by breast cancer patients.

Integrative Oncology is compiled by Barrie R. Cassileth, MS, PhD, Chief of the Integrative Medicine Service and Laurance S. Rockefeller Chair in Integrative Medicine, and Jyothirmai Gubili, MS, Editor of About Herbs, Memorial Sloan-Kettering Cancer Center. The free About Herbs website and the free About Herbs application are managed by K. Simon Yeung, PharmD, LAc, Memorial Sloan-Kettering Cancer Center.


Scientific name: Linum usitatissimum

Common names: Flax, linseed, lint bells, linum


Believed to have originated in ancient Egypt, flax is an annual plant cultivated worldwide. One of the world’s oldest crops, it has served many purposes. The fiber from the stem was used to produce cloth and fishnets, while the seeds were consumed as food.

The seeds and oil have also been used in traditional medicine to treat constipation and urinary tract infections, to control menopausal symptoms, and to treat coughs, colds, acne, and burns.

Flaxseed is rich in omega-3 fatty acids that are known to protect against a variety of medical problems including heart disease, arthritis, and inflammatory bowel disease. It also contains phytoestrogens called lignans, which exert anticancer effects in vitro. However, human data are limited. Also, because flaxseed contains phytoestrogenic lignans, patients with hormone receptor–positive breast cancer should consult their oncologists before taking flaxseed supplements.

Flaxseed is available in the form of whole seeds, oil, capsule, powder, and as linseed cakes in many grocery and health food stores. It is promoted as an anticancer and cardioprotective agent despite lack of conclusive clinical evidence.

The Science

Flaxseed has demonstrated chemo- and renoprotective effects in patients with lupus nephritis.1,2 Supplementation with a major lignan derived from flaxseed improved glycemic control in type 2 diabetic patients.3 Data on the cholesterol-lowering effects of flaxseed are mixed.4,5

Preclinical data indicate that flaxseed inhibits the growth and metastasis of breast6 and prostate cancer cells,7 as well as melanoma.8 It has also improved survival in mice by reducing radiation therapy–induced lung damage.9

In patients with prostate10 and breast cancers,11 flaxseed supplementation reduced tumor biomarkers. It was shown to benefit women with polycystic ovarian syndrome by reducing androgen levels.12 A moderate reduction of estrogens and androgens, which may afford protection against breast cancer, was also seen in postmenopausal women.13

Current data on the effects of flaxseed in relieving menopausal symptoms are limited and inconsistent.14,15 Additional studies are underway.16

Adverse Effects

Increased bowel movements,17 constipation and flatulence,18 and anaphylaxis19 have been reported following ingestion of flax.

A case of flaxseed mimicking polyposis coli, a significant risk factor for colorectal carcinoma, also was reported following flaxseed supplementation.20

Disclosure: Drs. Cassileth and Yeung and Ms. Gubili reported no potential conflicts of interest.


1. Haggans CJ, Hutchins AM, Olson BA, et al: Effect of flaxseed consumption on urinary estrogen metabolites in postmenopausal women. Nutr Cancer 33:188-195, 1999.

2. Clark WF, Kortas C, Heidenheim AP, et al: Flaxseed in lupus nephritis: A two-year nonplacebo-controlled crossover study. J Am Coll Nutr 20(suppl 8):143-148, 2001.

3. Pan A, Sun J, Chen Y, et al: Effects of a flaxseed-derived lignan supplement in type 2 diabetic patients: A randomized, double-blind, cross-over trial. PLoS ONE. 2(11):e1148, 2007.

4. Lemay A, Dodin S, Kadri N, et al: Flaxseed dietary supplement versus hormone replacement therapy in hypercholesterolemic menopausal women. Obstet Gynecol 100:495-504, 2002.

5. Fukumitsu S, Aida K, Shimizu H, et al: Flaxseed lignan lowers blood cholesterol and decreases liver disease risk factors in moderately hypercholesterolemic men. Nutr Res 30(7):441-446, 2010.

6. Chen J, Stavro PM, Thompson LU: Dietary flaxseed inhibits human breast cancer growth and metastasis and downregulates expression of insulin-like growth factor and epidermal growth factor receptor. Nutr Cancer 43:187-192, 2002.

7. Lin X, Gingrich JR, Bao W, et al: Effect of flaxseed supplementation on prostatic carcinoma in transgenic mice. Urology 60:919-924, 2002.

8. Yan L, Yee JA, Li D, et al: Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Lett 124:181-186, 1998.

9. Christofidou-Solomidou M, Tyagi S, Tan KS, et al: Dietary flaxseed administered post thoracic radiation treatment improves survival and mitigates radiation-induced pneumonopathy in mice. BMC Cancer 11:269, 2011.

10. Demark-Wahnefried W, Polascik TJ, George SL, et al: Flaxseed supplementation (not dietary fat restriction) reduces prostate cancer proliferation rates in men presurgery. Cancer Epidemiol Biomarkers Prev 17:3577-3587, 2008.

11. Thompson LU, Chen JM, Li T, et al: Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res 11:3828-3835, 2005.

12. Nowak DA, Snyder DC, Brown AJ, et al: The effect of flaxseed supplementation on hormonal levels associated with polycystic ovarian syndrome: A case study. Curr Top Nutraceutical Res 5:177-181, 2007.

13. Sturgeon SR, Heersink JL, Volpe SL, et al: Effect of dietary flaxseed on serum levels of estrogens and androgens in postmenopausal women. Nutr Cancer 60:612-618, 2008.

14. Lemay A, Dodin S, Kadri N, et al: Flaxseed dietary supplement versus hormone replacement therapy in hypercholesterolemic menopausal women. Obstet Gynecol 100:495-504, 2002.

15. Pruthi S, Qin R, Terstreip SA, et al: A phase III, randomized, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes: North Central Cancer Treatment Group N08C7. Menopause 19:48-53, 2012.

16. National Institutes of Health: [Open studies for flaxseed in cancer.] Available at Accessed March 4, 2013.

17. Cunnane SC, Hamadeh MJ, Liede AC, et al: Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr 61:62-68, 1995.

18. Demark-Wahnefried W, Price DT, Polascik TJ, et al: Pilot study of dietary fat restriction and flaxseed supplementation in men with prostate cancer before surgery: Exploring the effects on hormonal levels, prostate-specific antigen, and histopathologic features. Urology 58:47-52, 2001.

19. Leon F, Rodriguez M, Cuevas M: Anaphylaxis to Linum. Allergol Immunopathol 31:47-49, 2003.

20. Petty DR, Mannion RA: A case of multiple linseeds mimicking polyposis coli on double contrast barium enema. Clin Radiol 58:87-88, 2003.