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Deep Sea Nutrition: All About Seaweed

Gifts from the deep
By Kim Erickson
September/October 2001
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Wakame seaweed is high in protein and shown to suppress tumors.
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When you think of seaweed, do you have visions of slimy, brown tangles washing up on the shore? Or do you think of a nutritional powerhouse with medicinal properties? Both answers are correct, but many people don’t realize that seaweeds are beneficial to health, rapidly gaining popularity for their vitamin and mineral content, as well as their ability to prevent cancer and improve thyroid function.

Although often referred to as a vegetable, seaweed is actually any of the large multicelled forms of algae that live in fresh and salt water, especially along marine coastlines. While some may think of seaweed as part of an oceanic garden, it is different from higher land plants. Seaweeds lack true stems, leaves, and roots, and anchor themselves to rocks and reefs by rootlike holdfasts.

The three main phyla, or divisions, of seaweeds—which include some 15,000 species—are the familiar brown algae (Phaeophyta), such as kelp and bladderwrack; the reds (Rhodophyta), such as Irish moss; and the greens (Chlorophyta), which are often called sea lettuces.

Soaked in nutrition

What is it about seaweed that elevates it from simple fish food? Because seaweeds are constantly bathed in mineral-rich waters, they offer a wealth of nutrients, particularly iodine, calcium, potassium, magnesium, and iron. And depending on the variety, seaweed can be a good source of protein. A nutritional evaluation by Spain’s University Complutense of Madrid also found that seaweed is high in essential amino acids and unsaturated fatty acids.

Seaweed is packed with the immune-boosting vitamins A and C and some of the B vitamins. In fact, many types of seaweed contain more vitamin B12 than beef, chicken, or fish. A recent study by the Kochi Women’s University in Japan found that nori (Porphyra spp.), a form of red algae, is an excellent source of bioavailable vitamin B12, making it a nutritional boon for vegetarians. Seaweed is also high in a form of soluble fiber that may have antioxidant properties, particularly the fiber found in red and green algae. Another study by Japan’s Hiroshima University School of Medicine found that seaweed extracts can boost the immune system by stimulating the body’s B cells—white blood cells formed in the lymph nodes, spleen, thymus, and tonsils.

One drawback is that some types of seaweed are high in sodium. A half-cup of wakame (Undaria pinnatifida) contains approximately 900 mg of sodium, or nearly one-third of the daily sodium intake recommended by the American Heart Association. Fortunately, not all varieties pack such a sodium punch. The same amount of kelp (Laminaria spp.) dishes up 250 mg, and nori, a mere 60 mg. But if you are on a low-sodium diet or suffer from high blood pressure, you may want to check with your health-care practitioner before indulging at the sushi bar.

Because seaweed offers such a concentrated source of nutrition, some researchers and harvesters are touting it as one potential way to feed the earth’s growing population. Others are taking a look at the claims made for seaweed’s medicinal properties, including its reputation for treating hypothyroidism, obesity, cancer, and even cellulite. Could seaweed be the next miracle food? Let’s take a closer look at seaweed’s health claims.

Thyroid regulator

The thyroid gland is our internal thermostat, adjusting our body’s temperature by secreting hormones that control our metabolic rate. But occasionally the thyroid can become an underachiever, secreting too little of the hormones necessary to keep the metabolism running in top form. The result is hypothyroidism, a condition marked by fatigue, sluggishness, inability to tolerate cold environments, frequent infections (such as sinus infections) and painful menstruation. Hypothyroidism affects about 13 million Americans, 90 percent of whom are women, and may be caused by an autoimmune attack on the thyroid or an iodine deficiency. Exposure to environmental toxins, including lead, polychlorinated biphenyls (PCBs), and possibly bisphenol A (an industrial chemical found in some plastics and epoxy resins) may also contribute to the condition, as can excessive exposure to radiation from x-rays.

Seaweed has traditionally been the natural remedy of choice for hypothyroidism, particularly when the thyroid is enlarged (a condition known as goiter). The reasoning is that iodine, one of the key minerals in seaweed, is essential for normal thyroid function. According to Ryan Drum, Ph.D., professor of herbalism and lecturer at Dominion Herbal College in Vancouver, British Columbia, the two main thyroid hormones are T4, which consists of 65 percent iodine, and T3, which is made up of 59 percent iodine. Because iodine isn’t stored in the body, we must get a daily dose from our diets to keep these hormones functioning properly. Fortunately, most Americans get an adequate supply of iodine from their salt shakers. But if you don’t use iodized table salt, you may want to add a bit of kelp, or look for a seaweed extract that offers 150 mcg of iodine. But don’t overdo it—too much iodine can be as harmful as too little and may result in an overactive thyroid condition known as hyperthyroidism.

Iodine’s role in hypothyroidism has also been linked to weight gain. Because an iodine deficiency can result in a sluggish metabolism, some nutritionists and diet gurus recommend kelp supplements to help dieters lose stubborn pounds. Although kelp has enjoyed a long reputation as a weight-loss aid, said to help the body burn excess fat, there is no clinical evidence that it actually works. If you do suspect that excess weight is due to a glitch in your thyroid, ask your health-care practitioner to test for an iodine deficiency before you begin supplementing with seaweed.

Help for herpes

When we hear the word “herpes,” most of us think of either cold sores (herpes simplex virus type 1, or HSV-1) or the sexually transmitted infection that affects the genital area (HSV-2). But the herpes family contains several different viruses, including those responsible for chickenpox, shingles, Epstein-Barr and cytomegalovirus, which can lead to birth defects. The herpes virus is also suspected of having the potential to trigger autoimmune disorders, including multiple sclerosis and roseola. Although each herpes virus manifests itself in different ways, one thing they all have in common is that they are incurable in the eyes of conventional medicine.

But the sea may hold the answer to controlling, and possibly curing, herpes. Studies in the 1970s and 1980s found that red marine algae had significant antiviral properties, particularly when it came to herpes. Researchers concluded that the sulfated polysaccharides found in red marine algae enhance the immune system’s antiviral response by activating lymphocyte production, effectively inhibiting the virus. Proponents believe that all forms of red marine algae have antiviral properties and may reduce the severity and frequency of herpes outbreaks. But recent studies have so far found only two varieties of red marine algae that exhibit an anti-herpes effect. One study by the Bulgarian Academy of Sciences found that dillwyn (Polysiphonia denudata), a red algae from the Black Sea, inhibited the reproduction of both HSV-1 and HSV-2. Other studies by the University of Buenos Aires in Argentina discovered another variety of red marine algae (Nothogenia fastigiata), with antiviral activity against four different strains of HSV-1.

Getting the lead out

Seaweed may also play a role in reversing heavy metal toxicity. According to a recent report by the Centers for Disease Control and Prevention, America’s toxic load for lead is declining, but our bodies are still subjected to low levels of arsenic, mercury, nickel, and cadmium in our air, water, and food, and through countless human-made chemicals. Even at low levels, most heavy metals that reach the bloodstream are deposited into the tissues within forty-eight hours of exposure. If these toxins accumulate in the body faster than our natural detoxification pathways can purge them, they can have a negative impact on our endocrine, gastrointestinal, immune, reproductive, urinary, and nervous systems.

According to Elson Haas, M.D., co-author of Vitamins for Dummies (IDG, 1999), algin-rich kelp binds lead and other heavy metals and removes them from the body. Kelp’s high calcium content may also reduce the amount of toxic metals that are absorbed. But kelp isn’t the only seaweed capable of combating heavy metals. The polysaccharides found in red marine algae, particularly Irish moss (Chondrus crispus), are also thought to bind and eliminate heavy metals. Better yet, red marine algae has antibiotic and immune-boosting properties, which help protect our bodies from invading toxins.

Oceans of osteoporosis aid

We all know that calcium can help guard against osteoporosis—the progressive disease that weakens the mass and density of our bones. Thanks to the media’s attention to this potentially debilitating condition, American women are swallowing more calcium supplements and eating more dairy than ever before. Although adding additional calcium to your diet can be a good thing, what really matters is how well your body absorbs and utilizes this important mineral.

What can you do to boost your body’s ability to absorb calcium? Add seaweed! Rats on a low-calcium diet were fed seaweed mixed with oyster-shell calcium by researchers at the Calcium Research Institute in Osaka, Japan. The seaweed increased the rats’ intestinal absorption of calcium and prevented the decrease in bone density. Better yet, the same researchers recently conducted a randomized, double-blind study of fifty-eight elderly women and found that bone mass and density increased significantly when 900 mg of the oyster shell and seaweed calcium supplement was added to their daily diet.

The new cancer cure?

Among seaweed’s many medicinal uses, the most valuable may be its potential to prevent and treat cancer. Promising research has shown that this traditional Chinese cancer remedy may actually be a natural cytotoxin, a substance that has a specific toxic effect on certain cells. One variety of red seaweed, Porcheria hornaminyahae, was tested in the mid-1980s by the

National Cancer Institute and was found to contain a chemical that killed cancer cells. An in vitro study conducted at the Sapporo Medical University School of Medicine in Japan found that the holdfasts of kelp contain L-tryptophan, an essential amino acid. Although L-tryptohphan is not normally thought of as a cancer cure, the researchers found that the L-tryptophan derived from kelp inhibited breast cancer.

What’s more, seaweed has been found to inhibit the formation of tumors. A test of 306 species of marine algae at Saga University in Karatsu, Japan, found forty-seven varieties that demonstrated strong anti-tumor activity. And a French study found that one of the sea lettuces, green laver (Ulva lactuca), provides oligosaccharides, which may stop the multiplication of cancerous cells.

Although the study of seaweed’s anti-tumor activity is in its infancy, there are a few commonly eaten seaweeds that show potential. Japanese researchers have discovered that hijiki (Hijikia fusiformis) seems to stimulate T cells, the body’s natural killer cells. And other Japanese studies show that nori and wakame may have the ability to suppress chemically induced tumors. According to Alfred A. Bushway, Ph.D., professor of food science at the University of Maine, seaweed’s potential cancer-fighting abilities may be due to its high concentration of sodium alginate, “but this is a research area that needs to be more fully explored,” he says.

Whatever future research yields, one thing is clear: Seaweed is a tasty way to take your vitamins and minerals. And it doesn’t take much, notes Bushway. “Nutritional studies indicate that as little as a quarter-ounce per day can make a significant nutritional contribution to your diet.”

Seaweed’s beautiful benefits

For centuries, women have looked to the sea to enhance their looks. Thalassotherapy, the use of seaweed in holistic beauty treatments, has a long history of use in European spas. More recently, seaweed has gotten attention for its use in many popular cosmetics. Even though cosmetic manufacturers have been using the emulsifying and stabilizing properties of seaweed in their products for decades, they are now touting seaweed as a way to moisturize, firm and reduce sebum in the skin.

Can seaweed really help troubled skin, or is this just another marketing ploy? Proponents of seaweed’s ability to remineralize the body and foil the harmful effects of pollution on the skin cite a French study from the University of Rennes that reportedly shows that the minerals in seaweed are readily absorbed by the skin and make their way into the bloodstream. But, notes the author of the study, “thalassotherapy works best if you swallow the story whole. It’s a mind-body thing.”

Beyond sushi

You don’t have to be a sushi connoisseur to enjoy the pleasures of seaweed. In fact, in the past twenty-four hours, you’ve probably eaten some sort of seaweed without even knowing it! Beer, ice cream, puddings, processed cheese and canned meat contain alginates, agar, and carrageenans—important food additives which all began life as seaweed.

Seaweed derivatives can also be found in organic fertilizers, pharmaceuticals, paints, textiles and cosmetics. It’s even one of the components in linoleum. In fact, seaweed plays such an important role in our modern lives—from the lettuce patch to the cosmetic counter—that this ancient remedy has become a $6 billion per year industry.

Seaweed varieties

Bladderwrack (Fucus vesiculosus)
Nutritional profile: A good source of iodine.
Health benefits: Absorbs water in intestines to form bulk. Anecdotal reports of its ability to treat obesity and hypothyroidism.
How it’s used: As a medicinal herb and in thalassotherapy (the use of seaweed in beauty treatments).

Dulse (Palmaria palmata)
Nutritional profile: High in iodine, iron, and calcium.
Health benefits: Used to treat hypothyroidism.
How it’s used: Fresh in salads or cooked in soups. It can also be used as a salt substitute.

Hijiki (Hijikia fusiformis)
Nutritional profile: A very mineral-rich, high-fiber seaweed with lots of calcium, iron, and phosphorus. Hijiki (sometimes called hiziki) also contains 10 to 20 percent protein, along with some vitamin A.
Health benefits: Highly regarded in Traditional Chinese Medicine to treat goiter and high blood pressure. May stimulate T cells.
How it’s used: Cooked in soups, stews, and salads.

Kelp (Laminaria spp.)
Nutritional profile: Rich in iodine, calcium, potassium, and some of the B vitamins.
Health benefits: Binds heavy metals and is used to treat hypothyroidism.
How it’s used: As a seasoning.

Nori (Porphyra spp.)
Nutritional profile: Contains nearly 50 percent protein. Nori is high in vitamin A, calcium, iodine, iron, phosphorus, and fiber. Very high in vitamin B12.
Health benefits: Shown to suppress tumors.
How it’s used: Traditionally used to wrap sushi.

Red marine algae (Rhodophyta dumontiaceae)
Nutritional profile: A complete protein offering all of the essential amino acids, omega-3 and omega-6 essential fatty acids, calcium, magnesium, and potassium.
Health benefits: Immunomodulator and antiviral, particularly against herpes.
How it’s used: As a medicinal herb and supplement.

Wakame (Undaria pinnatifida)
Nutritional profile: Another high-protein seaweed, wakame contains calcium, iron, some vitamin A, and a small amount of vitamin C. It is high in sodium.
Health benefits: Shown to suppress tumors.
How it’s used: Primarily in soups.


Kim Erickson writes frequently on natural health and environmental issues.


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