Health Care Professional Information

Scientific Name
Linum usitatissimum
Common Name

Flax, linseed, lint bells, linum

Brand Name

Salinum ®, Brevail®

Clinical Summary

Flaxseed has been used in traditional medicine to treat coughs, colds, constipation, urinary tract infections, as a topical demulcent and an emollient (1). It is rich in omega-3 fatty acids and phytoestrogenic lignans.
Flaxseed was shown to have chemo- (2) and renoprotective effects in patients with lupus nephritis (3), and improved mild menopausal symptoms (11)
Supplementation with a major lignan derived from flaxseed improved glycemic control in Type 2 diabetic patients (13). Although flaxseed-derived lignan reduces blood glucose levels in hypercholesterolemic individuals (14), data on the cholesterol-lowering effects of flaxseed are mixed (11) (15) (26). Flaxseed supplementation may benefit women with polycystic ovarian syndrome by reducing androgen levels (23); a moderate reduction of estrogens and androgens was also seen in postmenopausal women (24). However, lignan supplementation was not effective in reducing hot flashes in postmenopausal women with or without breast cancer (28).

Flaxseed inhibits the growth and metastasis of human breast cancer (6) (29), prostate cancer (7) and melanoma (8) in vitro and in mice. It also reduces radiation therapy-induced lung damage and improves survival (27).
Flaxseed was also shown to lower tumor biomarkers in men with prostate cancer (9) (25) and in patients with breast cancer (10), but a flaxseed extract was ineffective in preventing oral infection following radiation treatment for head and neck cancer (12).

Flaxseed ingestion can increase urinary lignan excretion (4) and the length of the luteal phase of the menstrual cycle (5); it can also interfere with radiology procedures (18).

Purported Uses
  • Cancer prevention
  • Constipation
  • High cholesterol
  • Menopausal symptoms
  • Mucositis
  • Periodontal disease
  • Premenstrual syndrome
  • Radiation therapy side effects
Constituents

Flaxseed Oil: Unsaturated fatty acids including linolenic, linoleic and oleic acids.
Flaxseed soluble fiber: D-xylose, L-galactose, L-rhamnose, D-galacturonic acid and linusitamarin.
Flax leaves and seed chaff: Cyanogenic glycosides linamarin, linustatin and neolinustatin.(1)

Mechanism of Action

Flaxseed is the most concentrated food source of the plant lignan, secoisolariciresinol, a precursor for enterolactone. It is thought that these phytoestrogenic lignans contributes to its hormonal effects (4). Flaxseed has been shown to affect the length of the menstrual cycle in premenopausal women (5). Flaxseed may also alter estrogen metabolism, increasing the ratio of 2-hydroxyestrogen to 16 alpha-hydroxyestrone in a dose dependent fashion (2). Flaxseed's renoprotective effects are thought to come from high concentration of alpha-linolenic acid, an omega-3 fatty acid precursor (3) or through inhibition of angiogenesis, tyrosine protein kinases and cytokine-induced activation of transcription factors (16). Flaxseed may have laxative effect due to its fiber content (22).

In addition, flaxseed's inhibition of human breast cancer growth and metastasis in mice is due in part to its down-regulation of insulin-like growth factor I and epidermal growth factor receptor expression (6). It was also shown to induce apoptosis by significantly upregulating p53 mRNA in breast cancer cell lines (29). Its antiproliferative activity against prostate cancer in mice is attributed to its inhibition of cellular proliferation (7). The hormonal effects of flaxseed may also play a role in its ability to modulate prostate cancer biology and associated biomarkers (9) and lower serum lipid levels (10).

Pharmacokinetics

Absorption: Dose-dependent urinary lignan response to ingested flaxseed has been observed. Processing flaxseed does not affect lignan absorption. Plasma lignan concentration was greater than baseline, nine hours after flaxseed ingestion. No plateau in serum lignan concentration was observable in dosages up to 25 grams (20).

Contraindications

Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should use with caution.

Adverse Reactions

Common: Increased bowel movements (16), constipation and flatulence (9).
Case Reports:
Anaphylaxis due to flax ingestion has been reported (17) and workers regularly exposed to flax at their job show immunologically positive antigen tests (1).
A case of false polyposis coli on double contrast barium enema (18) and an increase in the luteal phase of the menstrual cycle (5) have also been observed after flaxseed supplementation.

Literature Summary and Critique

Zhang W, Wang X, Liu Y, et al. Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects. Br J Nutr. 2008;99:1301-9.
Fifty-five individuals with high cholesterol participated in this randomized, double-blind, placebo-controlled study. Participants were given flaxseed-derived lignan extracts (300 or 600 mg/day) or placebo for 8 weeks after which fasting blood glucose levels and lipid profiles were determined. Subjects who received 600 mg of extract had reductions in total cholesterol, LDL, and fasting blood glucose levels. Although other studies have reported discrepant effects on cholesterol levels by flaxseed, the authors postulate that these inconsistencies are due at least in part to the variable quantity of lignan within whole or defatted flaxseeds, a complication that is overcome with use of an extract.

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 2007; 2(11):e1148.
Effects of flaxseed-derived lignan supplementation in 68 type II diabetic participants were analyzed in this randomized, double-blind, cross-over study. After 12 weeks of receiving lignan supplements (360 mg/day) or placebo, the participants underwent an 8-week washout period before completing the remaining treatment arm. Glycemic control (as determined by HbA1c) was modestly affected by lignan supplementation; however, fasting glucose and insulin levels, insulin resistance, and blood lipid concentrations were unaltered. Because the influence of lignan on glycemic control was modest, additional studies are required to determine if it is clinically meaningful.

Brooks JD, et al. Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy. Am J Clin Nutr 2004;79:318-25.
In this study, 46 postmenopausal women were randomized to receive a placebo, soy (25 g soy flour), or flaxseed (25 g ground flaxseed) muffin for 16 weeks. Blood and 24-h urine samples were analyzed at baseline and at the endpoint for estrogen metabolites, serum hormones, and biochemical markers of bone metabolism. Results showed that the urinary concentrations of 2-hydroxyestrone, but not of 16alpha-hydroxyestrone increased significantly in the flaxseed group. There was no effect on the biochemical markers of bone metabolism. But since the study was limited by a short treatment time and fewer subjects, long-term studies with larger treatment groups are warranted.

Dosage (Inside MSKCC Only)
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References
  1. DerMarderosian A. The Review of Natural Products. St. Louis: Facts and Comparisons, 1999.
  2. Haggans CJ, Hutchins AM, Olson BA, Thomas W, Martini MC, Slavin JL. Effect of flaxseed consumption on urinary estrogen metabolites in postmenopausal women. Nutrition & Cancer. 1999;33:188-95.
  3. Clark WF, Kortas C, Heidenheim AP, Garland J, Spanner E, Parbtani A. Flaxseed in lupus nephritis: a two-year nonplacebo-controlled crossover study. Journal of the American College of Nutrition. 2001;20:Suppl-8.
  4. Hutchins AM, Martini MC, Olson BA, Thomas W, Slavin JL. Flaxseed influences urinary lignan excretion in a dose-dependent manner in postmenopausal women. Cancer Epidemiology, Biomarkers & Prevention. 2000;9:1113-8.
  5. Phipps WR, Martini MC, Lampe JW, Slavin JL, Kurzer MS. Effect of flax seed ingestion on the menstrual cycle. J Clin Endocrinol.Metab 1993;77:1215-9.
  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. Nutrition & Cancer. 2002;43:187-92.
  7. Lin X, Gingrich JR, Bao W, Li J, Haroon ZA, Demark-Wahnefried W. Effect of flaxseed supplementation on prostatic carcinoma in transgenic mice. Urology 2002;60:919-24.
  8. Yan L, Yee JA, Li D, McGuire MH, Thompson LU. Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Letters. 1998;124:181-6.
  9. Demark-Wahnefried W, Price DT, Polascik TJ, Robertson CN, Anderson EE, Paulson DF 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 2001;58:47-52.
  10. 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(10):3828-3835.
  11. Lemay A, Dodin S, Kadri N, Jacques H, Forest JC. Flaxseed dietary supplement versus hormone replacement therapy in hypercholesterolemic menopausal women. Obstetrics & Gynecology. 2002;100:495-504.
  12. Johansson G, Andersson G, Attstom R, Edwardsson S. Oral mucous membrane flora in patients using saliva substitutes. Gerodontology. 2000;17:87-90.
  13. 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 2007;2(11):e1148.
  14. Zhang W, Wang X, Liu Y, et al. Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects. Br J Nutr. 2008 Jun;99(6):1301-9.
  15. Jenkins DJ, Kendall CW, Vidgen E, Agarwal S, Rao AV, Rosenberg RS et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395-402.
  16. Cunnane SC, Hamadeh MJ, Liede AC, Thompson LU, Wolever TM, Jenkins DJ. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr 1995;61:62-8.
  17. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergologia et Immunopathologia. 2003;31:47-9.
  18. Petty DR,.Mannion RA. A case of multiple linseeds mimicking polyposis coli on double contrast barium enema. Clinical Radiology. 2003;58:87-8.
  19. Ranich T, Bhathena SJ, Velasquez MT. Protective effects of dietary phytoestrogens in chronic renal disease. Journal of Renal Nutrition. 2001;11:183-93.
  20. Nesbitt PD, Lam Y, Thompson LU. Human metabolism of mammalian lignan precursors in raw and processed flaxseed. Am J Clin Nutr. 1999;69:549-55.
  21. Brooks JD, Ward WE, Lewis JE, et al. Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy. Am J Clin Nutr 2004 Feb;79(2):318-25.
  22. Dahl WJ, Lockert EA, Cammer AL, et al. Effects of flax fiber on laxation and glycemic response in healthy volunteers. J Med Food. 2005 Winter;8(4):508-11.
  23. Nowak DA, Snyder DC, Brown AJ, Demark-Wahnefried W. The Effect of Flaxseed Supplementation on Hormonal Levels Associated with Polycystic Ovarian Syndrome: A Case Study. Curr Top Nutraceutical Res. 2007;5(4):177-181.
  24. Sturgeon SR, Heersink JL, Volpe SL, et al. Effect of dietary flaxseed on serum levels of estrogens and androgens in postmenopausal women. Nutr Cancer. 2008;60(5):612-8.
  25. 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. 2008 Dec;17(12):3577-87.
  26. Fukumitsu S, Aida K, Shimizu H, Toyoda K. Flaxseed lignan lowers blood cholesterol and decreases liver disease risk factors in moderately hypercholesterolemic men. Nutr Res. 2010 Jul;30(7):441-6.
  27. 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. 2011 Jun 24;11:269.
  28. 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. 2012 Jan;19(1):48-53.
  29. Lee J, Cho K. Flaxseed sprouts induce apoptosis and inhibit growth in MCF-7 and MDA-MB-231 human breast cancer cells. In Vitro Cell Dev Biol Anim. 2012 Apr;48(4):244-50.

Consumer Information

How It Works

Bottom Line: Flaxseed appears to be effective in reducing menopausal symptoms, however there is mixed evidence of its ability to reduce cholesterol levels.

Flaxseed is a very concentrated source of phytoestrogenic compounds called lignans, which have hormone-like effects on the body (soybeans are another source of phytoestrogens). These lignans are likely the reason why flaxseed can affect menstrual cycle length and menopausal symptoms. Flaxseed has also been shown to affect intracellular signals within the body that may play a role in breast and prostate cancer growth. It contains alpha-linolenic acid (ALA), a building block of omega-3 fatty acids. ALA has been shown to have numerous effects on the body including protecting the kidneys from damage. Results from clinical studies are mixed on flaxseed's ability to reduce cholesterol.

Purported Uses
  • Cancer prevention
    Studies of postmenopausal women showed that flaxseed supplementation improved the ratio of hormones that are thought to help prevent breast cancer. Studies in animals have shown promising results, however human data are lacking.
  • High cholesterol
    Study results are mixed.
  • Menopausal symptoms
    A study showed flaxseed to be as effective as hormone replacement therapy in the management of menopausal symptoms.
  • Mucositis
    One study indicated that flaxseed was not effective for mucositis.
  • Periodontal disease
    Flaxseed was shown ineffective against periodontal disease in a study.
Research Evidence

High Cholesterol:
Fifty-five individuals with high cholesterol were given flaxseed-derived lignan extracts (300 or 600 mg/day) or placebo for 8 weeks after which fasting blood glucose levels and lipid profiles were tested. Subjects who received 600 mg of extract had reductions in total cholesterol, low density lipoprotein (LDL or bad cholesterol), and fasting blood glucose levels.

Diabetes:
For this study, 68 type II diabetic participants received lignan supplements (360 mg/day) or placebo for 12 weeks. Subjects then underwent an 8-week washout period before receiving placebo. Glycemic control was modestly affected by lignan supplementation; however, there was no change in fasting glucose and insulin levels, insulin resistance, and blood lipid concentrations. Because the influence of lignan on glycemic control was modest, more studies are needed.

Postmenopausal Health:
In this study, 46 postmenopausal women were received a placebo, soy (25 g soy flour), or flaxseed (25 g ground flaxseed) muffin for 16 weeks. Blood and 24-hour urine samples were checked for estrogen metabolites, serum hormones, and biochemical markers of bone metabolism. Results showed that the urinary concentrations of 2-hydroxyestrone, but not of 16alpha-hydroxyestrone increased significantly in the flaxseed group. But there was no effect on the biochemical markers of bone metabolism.

Patient Warnings
  • Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should use flaxseed with caution.
Do Not Take If
  • You are undergoing radiological procedures as linseed may interfere with the reading of certain tests.
Side Effects
  • Allergic reaction
  • Increase of the luteal phase of the menstrual cycle
  • Increased bowel movement
  • Constipation
  • Flatulence
E-mail your questions and comments to aboutherbs@mskcc.org.