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Dr. Tori Hudson, Portland, Oregon, Blog Healthline Blog

As most of us know, breast cancer is the most common cancer in women, although lung cancer is more deadly. Integrating some aspect of natural medicine has become common place for women with breast cancer… at the very least, nutritional and exercise changes. The inclusion of flax seeds in the diet of breast cancer patients has been one nutritional influence that has been looked at in the research. Flax seed contains high concentrations of α-linolenic acid, ω-3 fatty acid, and a variety of lignans. Flax seeds are a dense source of the lignan secoisolariciresinol.

Several databases, including Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Embase, Embase Classic, and Allied and Complementary Medicine were searched through December 2, 2011. The review included controlled and uncontrolled human studies of women at risk of developing breast cancer or already diagnosed with cancer. The flax seed products included flax seed, flax seed-derived compounds, and flax seed oil. Hot flash occurrence, risk of breast cancer, breast cancer recurrence, breast cancer mortality, tumor characteristics, surrogate markers of breast cancer risk, and changes in hormonally responsive tissues were included as outcomes.

A total of1892 articles were retrieved from the databases and ten studies met the inclusion criteria. Only two of these studies were randomized, controlled trials. In the first study, ground flax seed bars were not found to significantly affect the rate of hot flashes compared to placebo bars in 135 women with breast cancer or a history of breast cancer. The second study measured biopsied breast tissue in 32 women with breast cancer before and after treatment with flax seed cooked into flax seed muffins. In the women who consumed the flax seeds, beneficial findings included an apoptotic index that increased significantly and human epidermal growth factor receptor 2 (HER2)  expression and Ki-67 labeling index, a marker of cell proliferation, both decreased significantly (−71.0% and −34.2%), respectively.

There were two trials without controls. One in which hot flashes decreased significantly with the consumption of 40 g of crushed flax seed per day. The second in which women consumed 50 mg of a lignan found in flax seed, for 12 months. In those with a positive response, there was a significant decrease in Ki-67 and atypical cell morphology of breast tissue.

In a single, nonrandomized, open-label study, biomarkers of angiogenesis in breast tissue were measured. Nine healthy women consumed 25 g flax seed and were compared to 11 patients with breast cancer undergoing tamoxifen treatment (20 mg daily). Flax seed and tamoxifen increased endostatin by approximately 33% in breast tissue, whereas tamoxifen, but not flax seed, decreased the other markers of angiogenesis.

Five observational studies were found. In two of these, consumption of lignans or flax seed (one quarter cup per day of flax seeds) resulted in a 19% or 20% reduction in the risk of developing breast cancer, respectively. The effect of flax seed was significant only in postmenopausal women. In a third observational study, no decrease in breast cancer risk was found with the consumption of a combination of sesame and flax seeds, although the amount was quite low at 1.42 mg/day. In another sesame/flax combination study, no effect on breast cancer mortality was seen, however, women in the study that consumed 0.3 to 3.5 g/day of sesame/flax were found to have a 31% reduction in overall mortality; but no advantage of > 3.6 gm/day. In the last observational study, a significant relationship was found between flax seed oil consumption and better mental health scores, as reported by the women, in women with breast cancer.

Commentary: This data in total, is encouraging in that it suggests that flax seed may decrease the incidence of breast cancer and may alter the growth of tumors through altering angiogenesis… which means limiting the blood supply to tumors. There also appears to be some advantage for postmenopausal women in that they may benefit more from the consumption of flax seed than do premenopausal women. Flax seeds contain phytoestrogen compounds, which some individuals have been concerned about. However, these compounds appear to be protective, especially in a low estrogen environment such as post menopause. There is a large body of scientific evidence that plants containing these phytoestrogen compounds, including three very large studies on soy products in breast cancer patients…may decrease the progression of breast cancer and women who eat soy regularly if not daily…will have a better outcome with their breast cancer. In addition, animal studies have found that flax seed and flax seed extracts reduce cell proliferation, angiogenesis, metastasis, and tumor size, and promote apoptosis.

Reference: Flower G, Fritz H, Balneaves LG, et al. Flax and breast cancer: a systematic review. Integr Cancer Ther. May 2014;13(3):181-192.

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