Can Flax Seeds Help Prevent Breast Cancer?

Image Credit: Alisha Vargas / Flickr. This image has been modified.

Preventing Breast Cancer with Flax Seeds

I’ve previously discussed the role of dietary lignans in the reduction of breast cancer risk and improvement in breast cancer survival, based on studies that showed that women with breast cancer who ate the most lignans appeared to live longer (Flaxseeds & Breast Cancer Survival: Epidemiological Evidence and Flaxseeds & Breast Cancer Survival: Clinical Evidence). However, lignans are found throughout the plant kingdom—in seeds, whole grains, vegetables, fruits, berries—so, how do we know lignans aren’t merely a marker for the intake of unrefined plant foods? For example, those who eat lots of plants—vegetarians—have about eight times the lignan intake compared to omnivores.

In a petri dish, lignans have been shown to both have direct anticancer growth activity against human breast cancer cells and to prevent cancer cell migration. But it wasn’t until 2005 that it was put to the test in people. Researchers from the University of Toronto conducted a randomized double-blind placebo-controlled clinical trial (as seen in my video, Can Flax Seeds Help Prevent Breast Cancer?) of flaxseeds, the world’s most concentrated source of lignans, in breast cancer patients. The researchers found that flax appears to have the potential to reduce human breast tumor growth in just a matter of weeks. Therefore, I started recommending ground flax seeds to breast cancer patients.

Can lignans also help prevent breast cancer in the first place? High lignan intake is associated with reduced breast cancer risk, but again lignan intake may just be saying an indicator of high plant food intake in general. So, researchers from the University of Kansas gave women at high risk for breast cancer a teaspoon of ground flaxseeds a day for a year, and found on average a drop in precancerous changes in the breast.

What about women who regularly eat flax seeds? Outside of an experimental setting, there just weren’t a lot of women eating flax seeds regularly to study—until now. Matching 3,000 women with breast cancer to 3,000 women without, a study published in Cancer Causes and Control found that consumption of flaxseed (and of flax bread) was associated with a 20–30 percent reduction in breast cancer risk. The researchers note that, as flaxseeds are packed with lignans, only a small daily serving of flaxseed is required to attain the level of lignan intake associated with a reduction in breast cancer risk. Researchers concluded: “As it appears that most women do not consume flaxseed and that small amounts may be associated with reduced breast cancer risk, interventions to increase the prevalence of flaxseed consumption might be considered.”

The latest review summarizes the association between flax and decreased risk of breast cancer, better mental health, and lower mortality among breast cancer patients. The only other study of flax and brain health I’m aware of was an exploration of 100 commonly used drugs and supplements on cognition in older adults, which found that flax is one of the few things that appears to help.

How else may flaxseeds aid in preventing and treating breast cancer? There’s an inflammatory molecule called interleukin-1, which may help tumors feed, grow, and invade. Our bodies therefore produce an interkeukin-1 receptor antagonist, binding to the IL-1 receptor and blocking the action of IL-1. The activity of this protective inhibitor can be boosted with the drug tamoxifen—or by eating flax seed. In premenopausal women, the proinflammatory profile of interleukin-1 can be counteracted by a dietary addition of a few spoonfuls of ground flax. One month of flax may be able to increase the anti-inflammatory inhibitor levels by over 50 percent, better even than the drug.

Yes, having one’s ovaries removed may reduce breast cancer risk as much as 60 percent, but at the cost of severe side effects. The drug tamoxifen may reduce the incidence of breast cancer by more than 40 percent, but may induce other severe side effects such as uterine cancer and blood clots. That’s why less toxic (even safe!) breast cancer preventive strategies, such as dietary modifications, need to be developed. These lignan phytoestrogens in flaxseeds may be one successful route given the data showing reduced breast cancer risk and improved overall survival.

Lignans are not a magic bullet to prevent breast cancer—we can’t just sprinkle some flax on our bacon cheeseburger—but as a part of a healthy diet and life-style, they might help to reduce breast cancer risk in the general population.

Flaxseeds may also help fight hormone-mediated cancers in men. See Flaxseed vs. Prostate Cancer and Was It the Flaxseed, Fat Restriction, or Both?

What else can these puppies do? See:

I have another 100+ videos on breast cancer if you want to become an expert and help take care of yourself and/or the women in your life. Here’s a few recent ones to get you started:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

34 responses to “Preventing Breast Cancer with Flax Seeds

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  1. I planted some flax seeds in my decorative food patch just to see what I’d get… pretty, tall blue flowers that bloomed happily all season, and I just harvested the heads and drying to get the seeds! Very cool, will definitely plant more! Glad I got the whole seeds to grind instead of the pre-ground.
    On another topic, Dr G needs to get that new recording of his presentation in the UK captioned! The auto captioning on youtube rots and I wanted to share it with some deaf and HH friends!

    1. the area where we live is a major grow area for flax, this summer I want pic of a large field of blue waving in the wind…if i remember will post it here sometime

        1. Had never looked into the different species of flax before.
          Linum lewisii – Wild Blue Flax, Lewis Flax, Prairie Flax. Wild Blue Flax is found in most of the western 2/3 of the United States. There are three recognized varieties found in North America; one found only in the United States, one found only in Canada, and a third found in both the United States and Canada – var. lewisii.

          A very similar species is the non-native Linum perenne, an import from Europe, which is found in scatterings across the United States. Some authorities treat the native L. lewisii as a subspecies of L. perenne – my guess is that the treatment may depend on which side of the Atlantic Ocean you call home. Many authorities call Linum perenne var lewisii a synonym of Linum lewisii.
          Cultivated flax, L. usitatissimum, is also similar in appearance.

          1. Interesting, not sure what mine was, it was just “golden flax”. Now I get why they used it to make material though, it grows so tall and straight, a lovely plant with pretty flowers, awesome seeds, and the potential to make cloth if you are really dedicated! Lately I’ve been planting a few seeds of any vegetable, bean, or even herb or spice seeds I buy just for the experience, pretty awesome! I found out fennel grows like crazy and swallowtail butterflies love it, mustard couldn’t be easier, and some legumes from the Indian market are amazingly adapted for dry climates! Seeds from store bought anything will grow, but you never know what you’ll get because they are mostly hybrids, but I’ve had a lot of luck and fun! I wish everyone would plant something for so many reasons!

            1. Cultivated flax, Linum usitatissimum. It is my understanding that there is only one species of cultivated flax.

              Flax (also known as common flax or linseed), with the binomial name Linum usitatissimum, is a member of the genus Linum in the family Linaceae. …The plant species is known only as a cultivated plant,[2] and appears to have been domesticated just once from the wild species Linum bienne, called pale flax.[3]

        2. ontario canada BTW wholesale price is up to 12,04 per 56 lbs canadian$ as China is buying and Russia had a low crop yield. Pretty sure the retail price remains the same about a buck. cheers

  2. In the Kansas study, about 20% of the women saw an increase in Ki-67 markers, and 3 of those were sharp increases! Can you please say something about this? Was that still a lot better than you’d expect to see in a group with similar risk factors? Otherwise, that study still leaves me wondering how to know if eating flax seed wouldn’t increase your cancer risks. (How do you know if you’d end up in the 80% with decreased markers or the 20% with increased ones?) The cumulative evidence from the other studies mentioned still suggests that flax is protective rather than a fertilizer for those markers, but I’d like to understand the graphs in that Kansas study better, and in a way that explains how the fact that 20% saw an increase shouldn’t raise concern. Also, other things I’ve read have reported that cadmium levels are high in flax seed, including organic seed, because it’s naturally in the soil in the regions where it’s usually grown. Cadmium is carcinogenic. It’s possible to buy flax seed from companies that grow it in regions that don’t have the cadmium, but it takes some effort to find them and costs more.

      1. Sorry to hear that. I don’t suppose you know what it was before eating the flax? This is the kind of result that scares me — and the reason I’d like to hear more about it from Dr. Greger. Maybe in that population in the study, which was high-risk to begin with, an increase like that would have been expected just in the normal course of things, without the flax seed. But if NOT, it’s hard not say that in those participants, at least, the flax probably increased their cancer risk.

    1. Hi Jennifer- thanks for asking such a great, and complicated, question!

      Letrozole (Femara) as you probably know is an aromatase inhibitor. It blocks the enzyme aromatase that is responsible for synthesizing estrogen in the body and therefore lowers the overall level of estrogen. This helps prevent estrogen from stimulating the growth of breast cancer cells. (Aromatase inhibitors are generally given after breast cancer treatment.)

      Flax, as we know from Dr. G’s website, has a lot of lignans. Lignans, some studies show, can act like estrogens in the body (Sturgeon). However, much of the literature on this is mixed. In general, the best human studies seem to show that flax counters the effects of estrogen or has other beneficial anticancer effects (Haggans, Brooks, McCann, Thompson, Dodin) just as Dr. G has been talking about. It would certainly be a good idea to talk to your physician before starting a diet high in flax though, especially if you are already on an aromatase inhibitor.

      Lots of info on flax:
      Brooks 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.

      Dalais et al. Effects of dietary phytoestrogens in postmenopausal women. Climacteric. 1998 Jun;1(2):124-9.

      Dodin et al. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab. 2005 Mar;90(3):1390-7

      Haggans et al. The effect of flaxseed and wheat bran consumption on urinary estrogen metabolites in premenopausal women. Cancer Epidemiol Biomarkers Prev. 2000 Jul;9(7):719-25.

      Lewis et al. A randomized controlled trial of the effect of dietary soy and flaxseed muffins on quality of life and hot flashes during menopause. Menopause. 2006 Jul-Aug;13(4):631-42.

      McCann et al. Changes in 2-hydroxyestrone and 16alpha-hydroxyestrone metabolism with flaxseed consumption: modification by COMT and CYP1B1 genotype. Cancer Epidemiol Biomarkers Prev. 2007 Feb;16(2):256-62.

      Sturgeon et al. Effect of dietary flaxseed on serum levels of estrogens and androgens in postmenopausal women. Nutr Cancer. 2008;60(5):612-8.

      Sturgeon et al. Effect of flaxseed consumption on urinary levels of estrogen metabolites in postmenopausal women. Nutr Cancer. 2010;62(2):175-80.

      Thompson et al. Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer. Clin Cancer Res. 2005 May 15;11(10):3828-35.

  3. No oil. Grind your flaxseed in a coffee grinder and store in fridge. Oil, none are healthy, attacks the endothelial cells the line your blood vessels leading to hardening of the arteries. Oil is just fat and has flummoxed the public into believing they need it. Use water, wine, beer etc to saute your onions and garlic.

    1. Yes but linseed/flaxseed oil is excellent for keeping your cricket bat in tip-top condition. In fact, it is an excellent preservative for many woods. Rumour has it that linseed oil explains Keith Richards’ longevity and current appearance. He is, after all, extremely well-preserved for a rockstar who has had so many years of hard living

  4. It is my understanding once you are diagnosed with ER+ breast cancer, you should not consume flax seed. Is this a correct conclusion? I check herbs and such on MSKCC website for any contraindications.

    1. One of the components mentioned was the lignans in flax. The lignin are associated with fiber. The flax oil is a more concentrated source of Omega 3 than the flax seed itself, but as an extracted oil, it doesn’t contain many of the other goodies that are in the fiber part of the seed. I would definitely give the beneficial edge to the whole flax seed. Dr. Greger’s Daily Dozen recommends just 1 tbsp of flax/day.

  5. I have raised this issue before. Considering that flaxseed and tamoxifen have a similar mode of action and considering that tamoxifen increases the risk of uterine cancer, it still needs to be determined that flaxseed does not increase the risk of uterine cancer as well. I am not aware that a study about this issue has been conducted. Until we know the answer, one cannot claim that flaxseed is necessarily safe.

  6. What’s the tastiest way to enjoy them regularly? I use them in cooking and I make yummy raw crackers with them, but I don’t usually get a tablespoon per day.

    1. I really like ground flax seed with my breakfast cereal. Some people put them in smoothies or just sprinkle over any food.

  7. The elephant in the room is Dairy.
    British scientist prof. Jane Plant CBE undergoing breast cancer radiation, surgery, chemo, and was eating yogurt to replenish her probiotics. Then she remembered. She had done research in rural China. The people there are lactose intolerant. They don’t do Dairy. They don’t get breast cancer.
    Prof. Plant had been measuring a persistent cancer tumor in her neck with calipers. She stopped eating dairy, the tumor linearly decreased and disappeared. Cow’s milk is intended to grow calves into cows in two years and has factors like IGF1 growth hormone. IGF1 hormone promotes growth in fast growing cells, in human adults that could be cancer cells. For detail see her book “The No Dairy Breast Cancer Prevention Program” (2002). The Program works. Verify, the breast cancer regions of the world are exactly the dairy regions.

    Flax seeds have lignans which raise the sex hormone binding globulin (SHBG) level. I”m an 81, male, testosterone O.K. but free testosterone off the bottom of the chart because of the binding action of my excess SHBG.

  8. Hi! Some years ago nutritionist tell me to use only seeds and when milling to use immediately and do not leave flexseeds powder at light/air. But now I see that powder are sold in bio markets: so it is possible to use it? Or it would be a waste of money because of oxydation? Otherwise I could mill all seeds by myself and maybe use also for backing if property are not lost with owen cooking :-)

  9. In Sweden, Livsmedelsverket (Swedens equivalent of FDA) and other health sites are not recommending eating ground flax seeds, due to flax seeds containing hydrogen cyanide. non-ground is OK, but only up to two table spoons.
    What is your take on that?

    Johan Böhlin

  10. I have read that eating certain types of hard cheeses, including gouda, edam, emmenthal and Jarlsburg, can lower your risk of developing cancer. Why? Because these cheeses contain a form of vitamin K called vitamin K2 (the scientific name is menaquinone) that is both antiangiogenic (blood vessel-inhibiting) and also kills cancer cells directly. The studies indicate that eating as few as 2 slices of these hard cheeses a day can lower your overall risk for cancer, including lung cancer and prostate cancer. You can find these cheeses in your local grocery store. I am going to keep having my cheese

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