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For Patients & Caregivers
Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.
What is it?
Flaxseed comes from the flax plant. It has omega-3 fatty acid, fiber, and a compound called lignin. Flaxseed is also a source of plant-based estrogens that have hormone-like effects in the body. They may help mild menopausal symptoms like hot flashes.
Flaxseed is in many different foods including crackers, waffles, and oatmeal. You can also get flaxseed whole or grounded to use in foods and drinks.
What is it used for?
Flaxseed is used to:
- Prevent breast, prostate, and colon cancer
- Control blood sugar level in patients with type-2 diabetes
- Lower high cholesterol
- Manage menopausal symptoms such as hot flashes and night sweats, but more research is needed to see if flaxseed actually helps with this.
Flaxseed also has other uses that haven’t been studied by doctors to see if they work.
It’s generally safe to use flaxseed in food and drinks but talk with your healthcare providers before taking flaxseed supplements. Herbal supplements are stronger than the herbs you would use in cooking.
Supplements can also interact with some medications and affect how they work. For more information, read the “What else do I need to know?” section below.
What are the side effects?
What else do I need to know?
For Healthcare Professionals
Flaxseed, rich in omega-3 fatty acids and phytoestrogenic lignans, has been used in traditional medicine to treat coughs, colds, constipation, urinary tract infections, and as a topical demulcent and emollient. In clinical studies, flaxseed improved mild menopausal symptoms (11); and exerted chemoprotective effects (2) along with affecting moderate reductions in estrogens and androgens (24) in postmenopausal women. It may also benefit women with polycystic ovarian syndrome by reducing androgen levels (23); and flaxseed powder combined with Vitex agnus may help to reduce cyclical mastalgia (39). Supplementation with a major lignin derived from flaxseed improved glycemic control in Type-2 diabetic patients (13). However, it was ineffective in reducing hot flashes in postmenopausal women with or without breast cancer (28).
In other studies flaxseed products were found to reduce blood pressure (1) (34) (40) (41). Daily intake of flaxseed powder lowered blood pressure in pre-diabetic patients but did not improve insulin resistance or glycemic indices (35) although conflicting data suggest otherwise (49). Supplementation along with lifestyle modification was more effective than lifestyle modification alone to manage metabolic syndrome (36) and non-alcoholic fatty liver disease (37) (46). Flaxseed was also found more effective than lactulose (47) and psyllium for improving symptoms of constipation (42). In patients with ulcerative colitis, both flaxseed and flaxseed oil may affect reductions in systemic inflammation (50) as well as disease severity (44). In addition, daily flaxseed oil consumption significantly decreased inflammatory markers related to cardiovascular disease (38), and may help reduce bone resorption (43) in hemodialysis patients. Flaxseed was also shown to confer renoprotection in patients with lupus nephritis (3), but additional studies are needed.
Although flaxseed-derived lignan reduced blood glucose levels in hypercholesterolemic individuals (14), data on its cholesterol-lowering effects are mixed (11) (15) (26).
Preclinical studies suggest that flaxseed may inhibit growth and metastasis of human breast (6) (29), prostate (7) cancers and melanoma (8); and reduce radiation therapy-induced lung damage and improve survival (27). It was also shown to lower tumor biomarkers in patients with prostate (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); and supplementation with secoisolariciresinol diglucoside, a lignan, was not superior to placebo in reducing proliferation in benign breast tissue of premenopausal women at increased risk of breast cancer (45).
Flaxseed ingestion can increase urinary lignan excretion (4) and the length of luteal phase of the menstrual cycle (5). Because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive (ER+) breast cancer should consult their physicians before using it.
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).
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).
Gynecomastia: In a 70-year-old male patient after taking flaxseed oil for three months to address hyperlipidaemia (48).