Common Names

  • Flax
  • Linseed
  • Lint bells
  • Linum

For Patients & Caregivers

How It Works

Flaxseed may help improve menopausal symptoms and reduce blood pressure, but evidence of its ability to improve cholesterol levels is mixed.

Flaxseed is a concentrated source of phytoestrogenic compounds called lignans, which have hormone-like effects on the body. These lignans are likely the reason why flaxseed can affect menstrual cycle length and menopausal symptoms. 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. Other studies suggest it may reduce blood pressure and help with some aspects of diabetes or related conditions, especially along with other lifestyle modifications. 

Flaxseed has also been shown to affect intracellular signals within the body that may play a role in breast and prostate cancer growth. Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should consult their physicians before using flaxseed.

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, but human data are lacking.
  • Diabetes and associated conditions
    Some studies suggest supplementation with flaxseed may help some aspects of diabetes or related conditions, especially along with other lifestyle modifications. 
  • 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.
Do Not Take If
  • You are undergoing radiological procedures: Flax or linseed may interfere with the reading of certain tests.
Side Effects
  • Allergic reactions
  • Longer luteal phase of the menstrual cycle
  • Increased bowel movement
  • Constipation
  • Flatulence

Case Reports

  • Anaphylaxis following intake of flaxseeds
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For Healthcare Professionals

Brand Name
Salinum®, Brevail®
Scientific Name
Linum usitatissimum
Clinical Summary

Flaxseed, rich in omega-3 fatty acids and phytoestrogenic lignans, has been used in traditional medicine to treat coughs, colds, constipation, and urinary tract infections. It has also been employed as a topical demulcent and as an emollient. In clinical studies, flaxseed improved mild menopausal symptoms (11) and exerted chemoprotective effects in postmenopausal women (2). It affected moderate reductions in estrogens and androgens in postmenopausal women (24), and may also benefit women with polycystic ovarian syndrome by reducing androgen levels (23). Flaxseed powder along with Vitex agnus may help to reduce cyclical mastalgia (39).

In other studies, supplementation with a major lignan derived from flaxseed improved glycemic control in Type-2 diabetic patients (13). However, lignan supplementation was ineffective in reducing hot flashes in postmenopausal women with or without breast cancer (28). Flaxseed products have also been shown to reduce blood pressure (1) (34) (40) (41). In prediabetic patients, daily flaxseed powder lowered blood pressure but did not improve insulin resistance or glycemic indices (35). Supplementation along with lifestyle modification was more effective than lifestyle modification alone to manage metabolic syndrome (36) and non-alcoholic fatty liver disease (37). Flaxseed was also found more effective than psyllium for improving symptoms of constipation, weight, as well as glycemic and lipid levels (42). In hemodialysis patients, daily flaxseed oil consumption significantly reduced inflammatory markers related to cardiovascular disease (38), and may help reduce bone resorption (43). Although flaxseed-derived lignan reduced blood glucose levels in hypercholesterolemic individuals (14), data on cholesterol-lowering effects are mixed (11) (15) (26). Flaxseed conferred renoprotection in patients with lupus nephritis (3), but additional studies are needed.

Flaxseed has been investigated for its anticancer potential as well. Laboratory studies suggest it may inhibit growth and metastasis of human breast (6) (29) and prostate (7) cancers as well as melanoma (8). Animal models suggest that it may reduce radiation therapy-induced lung damage and improve survival (27). Flaxseed was found to lower tumor biomarkers in patients with prostate cancer (9) (25) and breast cancer (10), but a flaxseed extract was ineffective in preventing oral infection following radiation treatment in head and neck cancer patients (12).

Flaxseed ingestion can increase urinary lignan excretion (4) and the length of the luteal phase of the menstrual cycle (5). Because it has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should consult their physicians before taking flaxseed.

Purported Uses
  • Cancer prevention
  • Constipation
  • Diabetes
  • High cholesterol
  • Menopausal symptoms
  • Mucositis
  • Periodontal disease
  • Premenstrual syndrome
  • Radiation therapy side effects
Mechanism of Action

Flaxseed is the most concentrated food source of the plant lignan, secoisolariciresinol, a precursor for enterolactone. It is thought that phytoestrogenic lignans contribute to the plant’s hormonal effects (4). Flaxseed has been shown to affect the length of the menstrual cycle in premenopausal women (5). It may also alter estrogen metabolism, increasing the ratio of 2-hydroxyestrogen to 16 alpha-hydroxyestrone in a dose-dependent fashion (2). The renoprotective effects of flaxseed are thought to be due to 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). The laxative effects of flaxseed are likely due to its fiber content (22).

Animal studies suggest inhibition of growth and metastasis of established human breast cancer with flaxseed is due in part to downregulation of insulin-like growth factor I and expression of the epidermal growth factor receptor (6). Flaxseed also induced apoptosis by significantly upregulating p53 mRNA in breast cancer cell lines (29). In another study, flaxseed oil enhanced effects of trastuzumab in reducing HER2 signaling via Akt and mitogen-activated protein kinase (MAPK) pathways, resulting in reduced cell proliferation and increased apoptosis (33). Inhibition of cell proliferation with flaxseed was also reported in models of prostate cancer (7).

In human studies, dietary flaxseed reduced central aortic blood pressure through changes in plasma oxylipins (40) (41). Other studies suggest hormonal effects may play a role in the ability of flaxseed to modulate prostate cancer biology and associated biomarkers (9), and lower serum lipid levels in postmenopausal breast cancer (10).

Adverse Reactions

Common: Increased bowel movements (16), constipation, and flatulence (9)

Case Reports
Anaphylaxis: Following ingestion of flaxseeds (17) (30).
False polyposis coli: On double contrast barium enema after flaxseed supplementation (18).
Increase in the luteal phase of the menstrual cycle: After flaxseed supplementation (5).

Dosage (OneMSK Only)
  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  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(10):3828-3835.

  8. 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.

  9. Johansson G, Andersson G, Attstom R, Edwardsson S. Oral mucous membrane flora in patients using saliva substitutes. Gerodontology. 2000;17:87-90.

  10. 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.

  11. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergologia et Immunopathologia. 2003;31:47-9.

  12. Petty DR,.Mannion RA. A case of multiple linseeds mimicking polyposis coli on double contrast barium enema. Clinical Radiology. 2003;58:87-8.

  13. Ranich T, Bhathena SJ, Velasquez MT. Protective effects of dietary phytoestrogens in chronic renal disease. Journal of Renal Nutrition. 2001;11:183-93.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Alvarez-Perea A, Alzate -Pérez D, Doleo Maldonado A, Baeza ML. Anaphylaxis caused by flaxseed. J Investig Allergol Clin Immunol. 2013;23(6):446-7.

  20. Zarepoor L, Lu JT, Zhang C, et al. Dietary flaxseed intake exacerbates acute colonic mucosal injury and inflammation induced by dextran sodium sulfate. Am J Physiol Gastrointest Liver Physiol. 2014 Jun 15;306(12):G1042-55.

  21. Herchi W, Arráez-Román D, Trabelsi H, et al. Phenolic compounds in flaxseed: a review of their properties and analytical methods. An overview of the last decade. J Oleo Sci. 2014;63(1):7-14.

  22. Ursoniu S, Sahebkar A, Andrica F, Serban C, Banach M; Lipid and Blood Pressure Meta-analysis Collaboration (LBPMC) Group. Effects of flaxseed supplements on blood pressure: A systematic review and meta-analysis of controlled clinical trial. Clin Nutr. 2016 Jun;35(3):615-25.

  23. Yari Z, Rahimlou M, Poustchi H, et al. Flaxseed Supplementation in Metabolic Syndrome Management: A Pilot Randomized, Open-labeled, Controlled Study. Phytother Res. Aug 2016;30(8):1339-1344.

  24. Yari Z, Rahimlou M, Eslamparast T, et al. Flaxseed supplementation in non-alcoholic fatty liver disease: a pilot randomized, open labeled, controlled study. Int J Food Sci Nutr. Jun 2016;67(4):461-469.

  25. Mirghafourvand M, Mohammad-Alizadeh-Charandabi S, Ahmadpour P, et al. Effects of Vitex agnus and Flaxseed on cyclic mastalgia: A randomized controlled trial. Complement Ther Med. Feb 2016;24:90-95.

  26. Caligiuri SP, Rodriguez-Leyva D, Aukema HM, et al. Dietary Flaxseed Reduces Central Aortic Blood Pressure Without Cardiac Involvement but Through Changes in Plasma Oxylipins. Hypertension. Oct 2016;68(4):1031-1038.

  27. Mirfatahi M, Imani H, Tabibi H, Nasrollahi A, Hedayati M. Effects of Flaxseed Oil on Serum Bone Turnover Markers in Hemodialysis Patients: a Randomized Controlled Trial. Iran J Kidney Dis. 2018 Jul;12(4):215-222.

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