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For Patients & Caregivers
How It Works
Flaxseed may help improve mild 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.
- 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
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).
In other studies, supplementation with a major lignan 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). Flaxseed products have also been shown to reduce blood pressure (1) (34) (40) (41). In pre-diabetic patients, daily intake of 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, as well as glycemic and lipid levels (42). In patients with ulcerative colitis, both flaxseed and flaxseed oil were reported to reduce inflammatory markers, disease severity, and blood pressure (44). Daily flaxseed oil consumption also significantly reduced inflammatory markers related to cardiovascular disease (38), and may help reduce bone resorption (43) in hemodialysis patients. Furthermore, flaxseed conferred renoprotection in patients with lupus nephritis (3), but additional studies are needed.
Flaxseed has also been investigated for its anticancer potential. Preclinical studies suggest it may inhibit growth and metastasis of human breast (6) (29), prostate (7) cancers and melanoma (8); and may reduce radiation therapy-induced lung damage and improve survival (27). Flaxseed was reported 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 the 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).