Seaweed is recommended for breast cancer in moderation
The category of seaweed, or ocean vegetables, includes edible seaweed or algae such as dulse, kelp (including arame, kombu, and wakame), nori, and sea lettuce (Ulva lactuca and Monostroma spp.). Generally speaking, seaweed is a good dietary source of calcium, iodine, iron, potassium, and fiber. Various seaweeds have been shown to have anti-inflammatory, antioxidant, anticoagulant, and antibiotic properties. Some varieties are also good sources of vitamin A, vitamin B6, vitamin B12, vitamin C, vitamin E, vitamin K, manganese, magnesium, selenium, copper, or zinc. Seaweed can be a rich source of carotenoids. For example, brown seaweeds contain beta-carotene, fucoxanthin, and violaxanthin. In addition, seaweed contains some unique compounds, such as various fucoidans (found in brown seaweeds), stearidonic acid (brown seaweeds), phlorotannins (kelp), mycosporine-like amino acids and phenolic acid (dulse), all of which have been shown to have anticancer properties in the laboratory. Various extracts of seaweed have been shown to inhibit the growth of colon and breast cancer cells in the laboratory.Breast cancer-related effects of consuming seaweed
The evidence that seaweed consumption could reduce the risk of breast cancer is based primarily on studies of brown seaweeds:
- Consumption of brown seaweeds has been shown to favorably alter estrogen metabolism in women. Extract of common kelp has been shown to inhibit the binding of estradiol to estrogen receptors and progesterone to the progesterone receptor. Bladderwrack (another type of edible kelp) has been found to exert anti-estrogenic effects in pre-menopausal women
- Specific unique components (fucoidan, fucoxanthin, alginic acid, laminarin) of brown seaweeds have been shown to inhibit cancer cell proliferation. However, red seaweeds, which lack these compounds, also inhibit proliferation, suggesting that other compounds found in seaweed may also be important
- Seaweed in the Asian diet may enhance intestinal conversion of phytoestrogens, in particular the production of equol, which could explain some of the breast cancer protective effects of dietary seaweed and soy
- The brown seaweed wakame (a type of kelp) has been shown to contain the omega-3 fatty acids eicosapentaenoic acid and stearidonic acid, which may favorably increase the omega-3/omega-6 polyunsaturated fatty acid ratio (which in turn is thought to reduce breast cancer risk). Some other types of seaweed have been found to contain docosahexaenoic acid, another marine omega-3 fatty acid
- Wakame was also found to reduce breast cancer proliferation in rats in one Japanese study
- Mekabu (wakame root) extract has been shown to induce cell death in human hormone receptor negative (ER-/PR-) breast cancer cells and to suppress mammary carcinogenesis in rats when administered in daily drinking water, without toxicity
- The relatively high iodine content of seaweed may contribute to reduction in risk of breast cancer. Supplementation with iodine (I2) has been shown to have a suppressive effect on the development and size of both benign and invasive neoplasias
- The relatively high levels of calcium found in seaweed are also thought to contribute to seaweed's chemopreventive effects.
We suggest consuming seaweed as food rather than fucoidan, kelp or other seaweed supplements since (1) as outlined above, various components of seaweed in addition to fucoidan or iodine may be responsible for seaweed's apparent anti-carcinogenic effects; (2) the compounds, minerals and fiber found in seaweed may act synergistically to reduce cancer risk; (3) safe and effective levels of fucoidan have not been established; (4) supplementation may result in increased blood thinning, depending on the formulation.
Additional comments
Most seaweed is dried after being harvested and must be rehydrated before use. Nori is a common seaweed ingredient in sushi. Currently, in the U.S., seaweeds are used mainly as a source of gums, gelling compounds and thickeners (such as agar) for use in foods such as ice cream, and some industrial applications.
Seaweed readily incorporates minerals from the surrounding water; minerals can account for more than one-third of seaweed dry matter. While this can make various seaweeds a rich source of beneficial micronutrients, it can also make them a dietary source of heavy metals, including arsenic. One analysis of dried seaweed samples purchased in London and over the Internet found that some contained unacceptable levels of arsenic. On the other hand, one study found that wakame is effective in preventing the absorption and reabsorption of dioxin from the gastrointestinal tract and therefore might be useful in treatment of humans exposed to dioxin.
Several types of freshwater microalgae, including spirulina and other types of blue-green algae, have been marketed as supplements in the U.S. since the early 1980s. Blue-green algae contain the omega-3 fatty acid alpha linolenic acid, which has been shown to have chemopreventive activities. However, such freshwater algae can also contain concentrated amounts of heavy metals, as well as toxic microcystins, depending on where it is grown. Whether or not they contain heavy metals, many microalgaes are not edible. In fact, they may be harmful if consumed, and there have been instances of microalgae supplements sold that turned out to be toxic. Therefore, consumers of such supplements should assure themselves of the reputability of the manufacturer.
Since seaweeds have varying amounts of iodine and other nutrients, it can be difficult to know how much is in any given supplement. People with thyroid disorders may find that their conditions are made worse by eating kelp or taking seaweed supplements. Some seaweed also contains large amounts of sodium, which can worsen high blood pressure for those susceptible. Seaweed can also interfere with Warfarin (coumadin) and other blood-thinning therapy.
Selected studies
Fucoidan from Laminaria cichorioides inhibits AP-1 transactivation and cell transformation in mouse epidermal JB6 cells American Association for Cancer Research (AACR) Int'l Conference on Frontiers in Basic Cancer Research, October 2009The present study was designed to evaluate the mechanism of action by which fucoidan, a sulfated polysaccaride extracted from brown seaweeds, exerts chemopreventive effects. Fucoidan has been shown to have anticoagulant and antithrombotic properties. In addition, unlike heparin (an anticoagulant), fucoidan is known to exhibit anticancer activities. In the study, fucoidan from Laminaria cichorioides, a type of brown algae, was shown to inhibit neoplastic cell transformation induced by epidermal growth factor or 12-O-tetradecanoylphorbol-13-acetate (a tumor promoter), but had less cytotoxic effect on JB6 mouse epidermal cells. The phosphorylation of extracellular signal-regulated kinases 1/2 and c-Jun N-terminal kinases normally induced by epidermal growth factor was inhibited by fucoidan. These results appeared to be due to the inhibition of phosphorylation of epidermal growth factor receptor. Fucoidan was shown to reduce c-fos or c-jun transcriptional activity in a dose-dependent manner, thereby attenuating the associated AP-1 transactivation activity. Further testing demonstrated that fucoidan directly interacted with epidermal growth factor, apparently preventing the binding of epidermal growth factor to its cell surface receptor. This could explain fucoidan's antitumor promoting effect. The authors comment that the study findings are the first to reveal a molecular basis for the anticarcinogenic action of fucoidan, which may partially account for the reported chemopreventive effects of brown seaweeds.
Fucoidan Induces Apoptosis through Activation of Caspase-8 on Human Breast Cancer MCF-7 Cells Journal of Agricultural and Food Chemistry, August 2009
The present study was designed to investigate the effect of fucoidan, a component of brown seaweed, on the induction of cell death in human breast cancer cells. Fucoidan has been shown to inhibit proliferation and induce apoptosis in several types of cancer cells. However, the related mechanism of action is not well understood. In the study, it was found that fucoidan reduced the viable number of MCF-7 breast cancer cells in a dose-dependent and time-dependent manner. However, fucoidan was not found to influence the viable cell number of normal human breast epithelial cells. The apoptosis assay showed that fucoidan induced internucleosomal DNA fragmentation, chromatin condensation, activation of caspase-7, -8, and -9, and cleavage of poly (ADP ribose) polymerase. In addition, Bid expression declined, whereas truncated Bid was found to increase with fucoidan treatment. Also observed was a reduction in cytosolic Bax and a remarkable increase in cytosolic cytochrome c. Caspase-8-specific inhibitor (z-ITED-fmk) was shown to cancel the cytotoxicity of fucoidan, activation of caspase-7, -8, and -9, and a number of changes in Bax, Bid, and cytochrome c. On the other hand, caspase-9-specific inhibitor was found to have a moderate inhibitory effect on the cytotoxicity induced by fucoidan. The authors conclude that fucoidan could induce apoptotic cell death through a caspase-8-dependent pathway in MCF-7 breast cancer cells.
Dietary Seaweed Modifies Estrogen and Phytoestrogen Metabolism in Healthy Postmenopausal Women Journal of Nutrition, May 2009
The current double-blind trial of seaweed supplementation with soy challenge was designed to evaluate the impact of seaweed and soy consumption on estrogen metabolism in women. Both seaweed and various soy foods are consumed on a daily basis in Japan, where rates of breast cancer for postmenopausal women are markedly lower than in the West. Differences in diet (especially soy consumption) and estrogen metabolism might explain a portion of the difference in risk of breast cancer. The study included 15 healthy postmenopausal women who were randomly assigned to one of two groups. The first group received seven weeks of 5 grams per day of Alaria, a brown seaweed. The second group received a placebo (maltodextrin). During week seven, all participants also consumed soy protein isolate (2 mg isoflavones/kg body weight per day). After a three-week break (washout period), each group was crossed over to the alternate supplement schedule. An inverse correlation was found between seaweed dose (mg/kg body weight) and serum estradiol (E2) (seaweed-placebo = y = 0.28 x dose – 42.8; r = 0.70; P = 0.003). This correlation was linear across the range of study participant weights. Soy protein isolate supplementation was also found to increase urinary genistein, daidzein, glycitein, and O-desmethylangolensin (P = 0.0001) and reduce enterolactone and matairesinol (P < 0.05). Both soy protein isolate and seaweed plus soy (SeaSoy) were found to increase urinary excretion of 2-hydroxyestrogen (P = 0.0001) and the ratio of 2-hydroxyestrogen to 16-hydroxyestrone (P = 0.01). For the five women who were equol excretors, soy increased urinary equol excretion (P = 0.0001). Most interestingly, the seaweed plus soy combination further increased equol excretion by 58% (P = 0.0001). Equol producers also were observed to have a 315% increase in the 2-hydroxyestrogen to 16-hydroxyestrone ratio (P = 0.001) while taking seaweed plus soy. The authors conclude that seaweed favorably alters estrogen and phytoestrogen metabolism and that these changes likely include modulation of colonic bacteria.
Seaweed as chemoprevention: From breast cancer epidemiology to breast cancer cell culture American Association for Cancer Research (AACR) Int'l Conference on Frontiers in Cancer Prevention Research, November 2006
The current study was designed to investigate the effect of seaweed extracts in human breast cancer and colon cancer cells. Breast cancer rates among women in the ongoing Japan Nurses' Health Study who consume miso soup six or more times per week have been found to have half the risk of breast cancer compared to women who consume miso soup infrequently. Since miso soup is essentially a hot water extract of seaweed, miso, and vegetables, this finding supports the many in vitro and in vivo studies that have reported seaweed-induced cancer inhibition. In Japan, five to seven grams (dry weight) of seaweed are eaten daily on average. The average is higher for nursing mothers. Although this may appear to be a small amount, seaweed expands to approximately 10 times its dry weight when refreshed in water, hence is a significant part of the diet. In the study, water extracts of a variety of common dietary seaweeds were tested in three cancer cell lines (estrogen receptor positive (ER+) MCF-7 breast cancer cells, estrogen negative (ER-) MDA-MB-231 breast cancer cells, and hormone insensitive HCT-15 colon cancer cells). Seaweed extracts were found to induce greater cancer cell inhibition in the hormone insensitive cancer cells tested (MDA-MB-231 and HCT-15). DNA synthesis was shown to be inhibited, and in the case of MDA-MB-231 breast cancer cells, clear cell cycle arrest in the G1 phase was observed. There was variation in the ability of different seaweeds to inhibit cancer cell proliferation. The authors note that while previous studies have demonstrated that specific unique components of brown seaweeds (i.e., fucoidan, fucoxanthin, alginic acid, and laminarin) can inhibit cancer cell growth, in this study it was found that red seaweeds, which lack these components, also induced similar inhibition. This suggests that other water soluble chemicals derived from seaweeds may also be important in elucidating the anticarcinogenic properties of dietary seaweeds.
Brown Kelp Modulates Endocrine Hormones in Female Sprague-Dawley Rats and in Human Luteinized Granulosa Cells Journal of Nutrition, February 2005
The present study was designed to investigate the endocrine modulating effects of kelp (Fucus vesiculosus) in female rats and in human luteinized granulosa cells. Population studies have reported that people consuming Asian diets have a lower risk of hormone-dependent cancers than those consuming Western diets. These differences often have been attributed to higher soy intakes among Asians. However, the anti-estrogenic effects of dietary kelp may also contribute to lower cancer rates among Asians. Previously, the authors conducted a pilot study of premenopausal women in which kelp consumption was found to be associated with endocrine modulation. In the present study, the impact of kelp administration on rat estrous cycles was assessed. Kelp was found to lengthen the rat estrous cycle from approximately 4.3 to 5.4 days at 175 mg per kg of body weight per day. Similarly, the cycle was lengthened to approximately 5.9 days at 350 mg of kelp and also led to a 100% increase in the length of diestrus. After 175 mg treatment for two weeks, serum 17ß-estradiol levels were reduced from approximately 48.9 to 40.2ng/L. After four weeks, 17ß-estradiol levels were reduced to 36.7. In human luteinized granulosa cells, 25, 50, and 75 µmol/L treatment reduced 17ß-estradiol levels from approximately 4732 to 3632, 3313, and 3060 ng/L, respectively. Kelp treatment also resulted in modest elevations in human luteinized granulosa cell progesterone levels. In addition, Kelp extract was found to inhibit the binding of estradiol to estrogen receptor and estrogen receptor ß and that of progesterone to the progesterone receptor. The authors conclude that kelp has endocrine modulating effects at relevant doses and suggest that dietary kelp may contribute to the lower incidence of hormone-dependent cancers among Japanese.
