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Frequently Asked Questions


I recently read an article in a Tufts University newsletter advising women to avoid flaxseeds if they are taking Tamoxifen. Can you help clarify this concern?

I have not seen that Tufts article, but I am familiar with the debate. This has been a very commonly asked question and difficult to answer as so little research has been done to date to try to address the concern if any molecular constituents in flaxseeds might inhibit Tamoxifen's anti-estrogen activity.

Dr. Lilian Thompson, one of the primary researchers who studies health effects of flaxseed consumption, published some of her research in 2003 (Breast Cancer Res Treat. 2003 Jul; 80(2): 163-70), in which she showed including flaxseed in the diet of mice with ER negative breast cancer that were also given tamoxifen, significantly reduced the bio-markers indicating that the cancer was metatasizing, versus giving either tamoxifen or flaxseed alone to identical mice. These results are valuable and important as they show that both tamoxifen and flaxseed are working against the breast cancer cells in additional ways that have nothing to do with estrogen metabolism. It is also particularly notable that not only did flaxseed not inhibit tamoxifen's beneficial effects but, in fact, increased them.

Dr. Thompson's laboratory also presented some additional research at the July 2003 AACR meeting held in Washington, DC. This research has now been published in a peer reviewed journal and has begun to shed some light on your question, which is being asked by many women taking Tamoxifen either after ER+ breast cancer or as a means of chemoprevention.

Dietary flaxseed enhances the inhibitory effect of tamoxifen on the growth of estrogen dependent human breast cancer (mcf-7) in nude mice, Chen J, Hui E, LU Thompson, Clin Cancer Res 2004 Nov 15;10(22):7703-11.

In a nutshell, this research showed that giving a dietary source of flaxseed with the anti-estrogen drug Tamoxifen to mice injected with estrogen-dependent breast cancer cells resulted in enhanced anti-cancer activity of the drug tamoxifen in both simulated pre- and post-menopausal situations.

Of additional interest, although this is a small study that needs repeating, it is notable (and very interesting) that at the end of this 6-week study, the low-estrogen group of mice given flaxseed without tamoxifen had a better rate of tumor regression than those given tamoxifen alone or those given tamoxifen + flaxseed. More of this type of research is urgently needed along with expanding this important animal research (critical for testing both safety and benefit and determining dosing) to humans. Enhancing current cancer therapies by modification of diet is potentially a safe, non-toxic, and low-cost way of improving long-term cancer survival odds.

The highly-regarded flaxseed researcher Lilian Thompson, PhD, is very careful and conservative with her recommendations regarding consumption of flaxseeds by women who have had, or are high risk for, ER+ breast cancer, since there have been no published studies showing any results from combining flaxseed and tamoxifen in human subjects. Thus organizations like the American Cancer Society (ACS) and the American Institute for Cancer Research (AICR) typically follow her recommendations, as do most other fine research scientists such as Wendy Demark-Wahnefried, PhD, RD at Duke University Cancer Center who is currently studying the effects of flaxseed in prostate cancer patients.

One additional research study that gives an added perspective on the general anti-cancer role that flaxseed consumption may have is published by Joanne Slavin, PhD at The University of Minnesota (Nutr Cancer 2001; 39(1): 58 - 65) showing that flaxseed consumption by healthy post-menopausal women significantly decreases the amount of the estrogen metabolite (17 beta-estradiol) that is considered more stimulatory for estrogen sensitive cells.

As I mentioned, this research needs to be repeated and expanded to human trials before recommending consumption of flaxseed will become standard practice in this situation. However, I have been consuming 1 - 2 Tablespoons of flaxseed daily since 1995, including the full 5 years that I was on tamoxifen, without a recurrence of my ER+ breast cancer.

I hope some of this information clears up some of your concerns. Please discuss this research and your food choices with your oncologist and the Registered Dietitian at your own cancer center. They should be able to also keep you up to date with new research as it becomes available.

faq posted 9/03, updated 2/04, updated 3/05


Back to Main QandA Page


Flaxseeds Is it safe to use flaxseeds whole? I have not found anything that will grind whole flaxseed.
Flaxseeds Is the omega-3 fatty acid content of brown flaxseeds and golden flaxseeds really different? updated 4/02
Flaxseeds Do you have more recipes using flaxseeds? posted 1/02, updated 4/02
Breast Cancer Should women with ER+ breast cancer avoid flaxseeds and flax oil that contain the phytoestrogens called lignans?
Flaxseeds Will taking my medications mixed with flaxseed powder and applesauce cause them to not be absorbed? posted 2/02
Flaxseeds How quickly does one need to eat ground flaxseed to prevent spoilage? posted 5/02
Flaxseeds What is the best way to clean out my coffee grinder when switching from grinding my coffee to flaxseeds? posted 12/02
Flaxseeds My husband had prostate cancer. Should he be avoiding flax? posted 4/03
Flaxseeds Does consuming flaxseeds potentially interfere with the anti-estrogen effect of Tamoxifen? posted 9/03, updated 2/04, updated 3/05
Flaxseeds Are flaxseeds safe to eat after heating? posted 1/04
Flaxseeds The May 2004 issue of Prevention Magazine says that women with ER+ breast cancer should not be eating flaxseeds. Do you agree? posted 4/04




These questions and answers are intended to be of a general informative nature. Please consult with the Registered Dietitian in your cancer center or your health care provider for nutritional advice that can be individualized to your specific medical condition.

Contact Diana:

Phone: 734/996-9260

Fax: 734/996-9262

P.O. Box 130221, Ann Arbor, MI  48113

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