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Seaweed and Breast Cancer

April 11, 2012 Written by JP       [Font too small?]

Seaweed is a familiar component in traditional Asian diets. Historical accounts indicate that the use of seaweeds such as gim (Porphyra sp.), kombu (Laminaria japonica) and miyeok (Undaria pinnatifida) in Japanese and Korean recipes have both a culinary and medicinal rationale. In recent years, scientists in the U.S. and abroad have begun to investigate the potential of edible seaweeds in relation to disease risk. In particular, cancer specialists and epidemiologists are investigating how and why seaweed may reduce the incidence of the most common malignancy among women: breast cancer.

In May 2010, a study presented in the British Journal of Nutrition reported that premenopausal women who ate the most seaweed were 56% less likely to be diagnosed with breast cancer than those who ate the least amount of seaweed (gim) in their daily diets. An analysis of postmenopausal women revealed an even more dramatic reduction of risk – 68% when comparing the highest to the lowest quintile of seaweed intake. But, not every type of seaweed afforded the same level of protection. Miyeok, a commonly consumed seaweed in Korea, did not confer the same protective effect as gim.

Currently, it’s unknown exactly why seaweeds may control the growth of malignant cells in breast tissue. Preliminary research has demonstrated that select phytochemicals in edible seaweeds (alginic acid, fucoidan, fucoxanthin and laminarin) interfere with the proliferation of cancer cells in an in-vitro environment. Human studies offer additional clues about possible mechanisms such as the ability to: a) reduce insulin-like growth factor 1, an anabolic hormone associated with the development of breast cancer; b) favorably alter estrogen metabolism and progesterone concentration; c) limit insulin spikes caused by the consumption of refined carbohydrates. High levels of circulating insulin and inadequate intake of iodine, a trace mineral found in seaweeds, are theorized as contributing to breast cancer incidence.

In our home, we regularly eat seaweed in the form of wrappers for rice-less “sushi” rolls. I’ve even been known to munch on dehydrated, seasoned seaweed snacks instead of chips or crackers. And, based on the data I’ve come across, I do believe it’s worthwhile for most women to include some seaweed in their diets. However, if you’re not accustomed to eating seaweed regularly, I would suggest introducing it gradually to establish tolerability. Just to be prudent, I would also suggest having periodic tests to rule out any unexpected or untoward changes in thyroid function that rarely occur when large amounts of iodine containing foods are consumed. I think this a reasonable way to proceed until more, well controlled studies evaluate the real world effects of seaweed in larger and more diverse populations.

Note: Please check out the “Comments & Updates” section of this blog – at the bottom of the page. You can find the latest research about this topic there!

To learn more about the studies referenced in today’s column, please click on the following links:

Study 1 - A Case–Control Study on Seaweed Consumption and the Risk of Breast (link)

Study 2 - Seaweed as Chemoprevention: From Breast Cancer Epidemiology to (link)

Study 3 - Serum IGF-1 Concentrations Change With Soy and Seaweed Supplements (link)

Study 4 - Dietary Seaweed Modifies Estrogen and Phytoestrogen Metabolism(link)

Study 5 - The Effect of Fucus Vesiculosus, An Edible Brown Seaweed, Upon (link)

Study 6 – A Randomised Crossover Placebo-Controlled Trial Investigating the (link)

Study 7 - Iodine: Deficiency and Therapeutic Considerations (link)

Study 8 - Metabolic Syndrome and Triple-Negative Breast Cancer (link)

Study 9 - Iodine Toxicity from Soy Milk and Seaweed Ingestion (link)

Study 10 – Suppression of Thyroid Function During Ingestion of Seaweed (link)

Elevated Insulin May Increase Breast Cancer Risk

Source: International Journal of Breast Cancer Volume 2012 (link)

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5 Comments & Updates to “Seaweed and Breast Cancer”

  1. Orna Izakson, ND, RH (AHG) Says:

    Another great one, JP!

    I find it interesting that Porphyra species showed such a good effect; nori, the Porphyra species eaten most commonly by Americans, is actually pretty low on the iodine scale. Do you think gim is pretty similar to nori? Just because it’s the same genus doesn’t mean it has the same effects.

    Also, you may be interested in the work of Ryan Drum, PhD, who’s a wildcrafter and herbalist in the San Juan Islands and a big expert on the medicinal uses of sea vegetables. His website is http://ryandrum.com/.

  2. JP Says:

    Thank you, Orna!

    My understanding is that nori is of one of several varieties of gim. Other seaweed such as bladderwrack have also demonstrated potential with regard to the promotion of breast health and estrogen metabolism.

    Even though nori isn’t as high in iodine as some other seaweeds, it still contributes a significant amount of the trace mineral to the average diet. Eating a serving a day could very well meet or surpass the iodine needs of most people.

    Thank you for sharing about Ryan’s site. I’ll most certainly check it out!

    Be well!


  3. JP Says:

    Updated 07/25/15:


    J Nutr. 2015 Jul 22.

    Iodine Supplementation Decreases Hypercholesterolemia in Iodine-Deficient, Overweight Women: A Randomized Controlled Trial.

    BACKGROUND: In iodine deficiency, thyrotropin (TSH) may increase to stimulate thyroidal iodine uptake. In iodine-sufficient populations, higher TSH predicts higher total cholesterol. Whether higher TSH caused by iodine deficiency affects serum lipids is uncertain.

    OBJECTIVE: Our aim was to determine if iodine repletion decreases serum TSH and improves the lipid profile.

    METHODS: In this randomized controlled intervention, iodine-deficient, overweight or obese Moroccan women (n = 163) received 200 μg oral iodine or a placebo daily for 6 mo. Main outcomes were serum TSH and plasma total and LDL cholesterol. Secondary outcomes included thyroid hormones and measures of lipid and glucose metabolism and urinary iodine concentration (UIC). Data were compared by using mixed-model analysis.

    RESULTS: In the intervention group, median UIC increased from 38 (95% CI: 34, 45) μg/L to 77 (95% CI: 59, 89) μg/L (P < 0.001). After 6 mo of intervention, TSH was 33% lower in the treatment group than in the placebo group (P = 0.024). The triiodothyronine (T3) to thyroxine (T4) ratio and thyroglobulin decreased with treatment [-15% (P = 0.002) and -32% (P < 0.001), respectively], whereas T4 concentrations were higher in the treatment group (P < 0.001). Total cholesterol in subjects with elevated baseline cholesterol (>5 mmol/L) was reduced by 11% after the intervention (P = 0.034). At 6 mo, only 21.5% of treated women remained hypercholesterolemic (total cholesterol >5 mmol/L) vs. 34.8% of controls (baseline: 44.2% in the intervention and 36.8% in the control group; P = 0.015). The reduction in the prevalence of elevated LDL cholesterol (>3 mmol/L) seen in the intervention group (50.6% to 35.4% compared with 47.4% to 44.9% in the control group) was not significant (P-interaction = 0.23).

    CONCLUSIONS: Our findings suggest that moderate to severe iodine deficiency in overweight women elevates serum TSH and produces a more atherogenic lipid profile and that iodine supplementation in this group reduces the prevalence of hypercholesterolemia. Thus, iodine prophylaxis may reduce cardiovascular disease risk in overweight adults.

    Be well!


  4. JP Says:

    Updated 08/26/15:


    Mar Drugs. 2014 Sep 24;12(9):4898-911.

    Anticancer effects of different seaweeds on human colon and breast cancers.

    Seafoods and seaweeds represent some of the most important reservoirs of new therapeutic compounds for humans. Seaweed has been shown to have several biological activities, including anticancer activity. This review focuses on colorectal and breast cancers, which are major causes of cancer-related mortality in men and women. It also describes various compounds extracted from a range of seaweeds that have been shown to eradicate or slow the progression of cancer. Fucoidan extracted from the brown algae Fucus spp. has shown activity against both colorectal and breast cancers. Furthermore, we review the mechanisms through which these compounds can induce apoptosis in vitro and in vivo. By considering the ability of compounds present in seaweeds to act against colorectal and breast cancers, this review highlights the potential use of seaweeds as anticancer agents.

    Be well!


  5. JP Says:

    Updated 08/26/15:


    J Appl Phycol. 2013 Jun;25(3):771-779.

    The consumption of seaweed as a protective factor in the etiology of breast cancer: proof of principle.

    Daily consumption of seaweed has been proposed as a factor in explaining lower postmenopausal breast cancer (BC) incidence and mortality rates in Japan. This clinical trial assessed the impact of introducing seaweed- to non-seaweed-consuming American postmenopausal women. Fifteen healthy postmenopausal women were recruited for a 3-month single-blinded placebo controlled clinical trial; five had no history of BC (controls) and ten were BC survivors. Participants ingested ten capsules daily (5 g day-1) of placebo for 4 weeks, seaweed (Undaria) for 4 weeks, then placebo for another 4 weeks. Blood and urine samples were collected after each treatment period. Urinary human urokinase-type plasminogen activator receptor concentrations (uPAR) were analyzed by ELISA, and urine and serum were analyzed for protein expression using surface-enhanced laser desorption/ionization-time-of-flight mass spectrometry (SELDI-TOF-MS). Urinary creatinine standardized uPAR (in pg mL μg-1 creatinine) changed significantly between groups, decreasing by about half following seaweed supplementation (placebo 1, 1.5 (95 % CI, 0.9-2.1) and seaweed, 0.9 (95 % CI, 0.6-1.1) while placebo 2 returned to pre-seaweed concentration (1.7 (95 % CI, 1.2-2.2); p = 0.01, ANOVA). One SELDI-TOF-MS-identified urinary protein (m/z 9,776) showed a similar reversible decrease with seaweed and is reported to be associated with cell attachment. One serum protein (m/z 8,928) reversibly increased with seaweed and may be the immunostimulatory complement activation C3a des-arginine. uPAR is higher among postmenopausal women generally, and for BC patients, it is associated with unfavorable BC prognosis. By lowering uPAR, dietary seaweed may help explain lower BC incidence and mortality among postmenopausal women in Japan.

    Be well!


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