Flaxseed Lignans

Flaxseed contains many components beneficial to health: lignans, fiber, magnesium, thiamin and an omega-3 fatty acid. In this summary, we focus on the lignans, natural plant compounds concentrated in flaxseed but also found in several other plant foods.

Clinical Practice Guidelines

According to the Society for Integrative Oncology’s 2009 clinical practice guidelines, there is insufficient evidence to rate the effectiveness of flaxseed lignans for helping quality of life or hot flashes.1

Treating the Cancer

Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action

Clinical Evidence

Enterolactone, a metabolite of flaxseed, is associated with decreased mortality rate and improved overall survival particularly in breast, prostate, colon, gastric and lung cancer.2

A 2018 review concluded that whole flaxseed, but not flaxseed oil and lignan extract, improved glycemic control and insulin levels and insulin sensitivity indexes when used 12 weeks or more.3

Breast Cancer

  • Anticancer effects among newly diagnosed breast cancer patients, including reduced tumor growth4
  • Increased cell death (apoptosis) and other tumor biological markers among women with postmenopausal breast cancer.5
  • Lower mortality among breast cancer patients in observational evidence6
  • Lower overall mortality in postmenopausal breast cancer patients who have high estimated enterolignan—a metabolite of flaxseed and other lignans—and dietary fiber, which is also abundant in flaxseed7

Prostate Cancer

  • In a randomized controlled trial looking at the effects of low-fat and/or flaxseed-supplemented diets on prostate cancer biology and biomarkers, flaxseed consumption was safe and associated with reduced proliferation rates, although no effect was seen on rate of cell death (apoptosis), PSA or IGF-I.8
  • A single study in 2004 suggested that men eating the highest amounts flaxseed oil had higher risk for prostate cancer progression,9 leading to speculation that dietary intake of α-linolenic acid (ALA)—found mainly in flaxseed and other foods—increases the risk of prostate cancer. However, authors of a subsequent meta-analysis “failed to confirm an association between dietary α-linolenic acid intake and prostate cancer risk.”10

Lab and Animal Evidence

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Managing Side Effects and Promoting Wellness

Managing or relieving side effects or symptoms, reducing treatment toxicity, supporting quality of life or promoting general well-being

Clinical Evidence

  • Better mental health among breast cancer patients in observational data15
  • Some evidence shows flaxseed reduced the incidence or frequency of hot flashes in women not taking estrogen therapy16 and postmenopausal women with or without breast cancer.17 However, a review concluded that flaxseed was ineffective in reducing hot flashes in postmenopausal women, either with or without breast cancer.18

    Lab and Animal Evidence

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Reducing Risk

Reducing the risk of developing cancer or the risk of recurrence

Clinical Evidence

  • Flaxseed lignans are reported to reduce the risk of primary breast cancer in observational clinical data.21 In a survey of women's consumption of phytoestrogen-containing foods, lignan intake was associated with reduced breast cancer risk among pre-menopausal women, with stronger associations among overweight women (body mass index over 25).22
  • Flaxseed consumption is associated with reduced risk or occurrence of colorectal cancer.23
  • Enterolactone, a metabolite of flaxseed, is associated with reduced risk, particularly in breast, prostate, colon, gastric and lung cancer.24

Cautions

Do not heat flaxseed oil, as the heat will damage the oil and form dangerous compounds.25 Heating flaxseed also removes many beneficial micronutrients.26

About Herbs cautions that because flaxseed has phytoestrogenic effects, patients with estrogen receptor positive breast cancer should use flaxseed lignan with caution. However, their summary on flaxseed did not cite any studies to back up this caution. A 2013 review of studies of flaxseed and breast cancer findings:

In vitro, flaxseed metabolites such as ENL [enterolactone] have been shown to interact with estrogen receptors behaving as weak estrogen agonists. While this action may be of concern to women with breast cancer, flaxseed administration appears to have no significant effect on endogenous estrogen levels in the majority of human trials, either in women with cancer or in healthy women. Conversely, studies that do report significant changes cite decreases in serum estrogen levels, suggesting reduced exposure to endogenous estrogen over time with flaxseed consumption. Fabian et al assessed the effect of 50 mg of SDG [a flax lignon precursor] on breast density over a 12-month period. Mammographic assessment found no significant change from baseline in breast tissue density following this intervention. These results lend further support to the notion that flaxseed does not appear to have a significant estrogenic effect in vivo.27

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Access

Both dietary flaxseed and flaxseed extract are widely available.

Dosing

BCCT does not recommend therapies or doses, but only provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated.

Human studies are limited but suggest that if anything, including one to four tablespoons of flaxseed per day might reduce breast cancer risk, especially in post-menopausal women.

AICR consultant Karen Collins, MS, RDN, CDN, FAND

Dosage recommendations are available from these sources:

A blog post from the American Institute for Cancer Research advises: "Human studies are limited but suggest that if anything, including one to four tablespoons of flaxseed per day might reduce breast cancer risk, especially in post-menopausal women.”32

Integrative Programs, Protocols and Medical Systems

For more information about programs and protocols, see our Integrative Programs and Protocols page.

Written by Laura Pole, RN, MSN, OCNS, and Nancy Hepp, MS; last updated on July 29, 2019.

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