Sea Vegetables

There are lots of things we want to do in life. Climb a mountain, write a song, watch our grandchildren grow up. But guess what? We can’t do any of those things if we don’t have our health.

Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to bring you evidence-based research that takes the mystery out of the best way to live a healthier, longer life.

If you thought vegetables only grew on land, you are deliciously mistaken. I’m talking about those very special foods we eat that are harvested from the ocean.  Still need a clue?  Yep.  That would be seaweed.

In our first story we discover how excessive intake of kelp, also known as kombu or thyroid-containing sausages can lead to iodine toxicity.

In this study of Boston vegans, concerns were raised about their iodine status, but one vegan’s iodine level was so high, they were excluded from the study. How is that possible? They were consuming kelp. As I’ve written in my iodine recommendations for a decade now, unless your neighborhood nuclear plant just melted down, no kelp. It just has too much iodine. And if you find yourself in Namibia, you might want to stay away from paddle weed as well. Other than that, though, and staying away from hijiki, which just has too much arsenic, sea vegetables are an excellent source of iodine.

There have been a few recent case reports of iodine toxicity in breastfeeding women eating soup made from kelp, also known as kombu, which explains this: “Iodine toxicity from soy milk.” Why? because it was made with kombu. But if you just read kombu on a label, would you think anything of it? Well, we should. There was a worldwide recall, complete with headlines like: “Café raid seizes banned soy milk.” A black market trade was operating in the banned soy milk, even though they faced half million dollar fines. That particular brand has since been reformulated without kombu.

The other way you can get in trouble with your thyroid gland is if you eat too many of them: “Hyperthyroidism caused by excessive consumption of sausages. After tests of the sausage revealed levels one might find in a dose of a thyroid hormone drug, like Synthroid, they “concluded that this patient had an exogenous hyperthyroidism caused by excessive intake of thyroid-containing sausages.”

Did you know that Nori seaweed snacks may favorably alter estrogen metabolism by modulating women’s gut flora, resulting in decreased breast cancer risk.

Unfortunately, as the traditional diets of East Asia Westernize, their breast cancer rates have risen, which some have linked to a quadrupling of animal product consumption.

We’ve known for over a decade that in vitro, in a petri dish, seaweed broth is effective at clearing cancer cells. But, what about outside of the test tube, in people?

Well, a population study comparing women with breast cancer, to women without, found that consuming a single sheet of nori a day may cut a woman’s odds of breast cancer in half. We think it’s because seaweed favorably alters estrogen metabolism, likely due to a modulation of the woman’s gut bacteria. It appears the more seaweed you eat, the less estrogen you have in your system, which may lower breast cancer risk.

This may be because of all the fiber in sea vegetables. Or, it may block the enzyme that undermines our body’s attempt to flush out excess hormones or, even somehow interfere with estrogen binding to estrogen receptors. Either way, to effectively lower one’s estrogen levels, Asian women may be able to get away with maybe one sheet of nori a day. But, American women are so much bigger that it may take closer to two. There’s lots of yummy seaweed snacks out there to make it a tasty experience, just try to get some low-fat, low-sodium ones.

Wakame, the seaweed used fresh in seaweed salads, unfortunately did not appear to reduce breast cancer risk, though it has been found to rather dramatically lower blood pressure in hypertensives. Just two teaspoons of seaweed salad a day for a month dropped their blood pressure 14 points. And, after two months, was associated with up to a two-inch skinnier waistline.

As I’ve mentioned before, though, I’d recommend avoiding hijiki, which tends to have too much arsenic, and kelp, which tends to have too much iodine. In fact, too much seaweed of any type may actually increase one’s risk of thyroid cancer, because of the amount of iodine you’d be taking in.

But, there does not appear to be increased risk at the levels of consumption I’m talking about; like, you know, a sheet of nori every day. And, a study of seaweed eaters in California actually found decreased risk. But, again, we’re talking, you know, kind of modest levels of intake.

You know, I’ve frequently talked about the benefits of dietary diversity, eating different families of fruits and vegetables, eating different parts of individual plants; like beets, and beet greens. If we just stick to land plants, though, we’re missing out on all the plants from the other 70% of planet Earth. Sea vegetables have phytonutrients found nowhere else, types of fiber, and unique carotenoids, and polysaccharides, and various polyphenol defense compounds, each of which may have anticancer properties. So, I encourage everyone to try experimenting with sea vegetables until you find one you like, even if that means just sprinkling some powdered dulse on your food.

In our final story we look at how eating seaweed salad may boost the efficacy of vaccinations and potentially help treat cold sores, herpes, Epstein-Barr virus, and shingles.

Billions of pounds of seaweed are harvested each year, the “consumption of which has been linked to a lower incidence of chronic diseases,” both physical and mental. For example, women who eat more seaweed during pregnancy appear to be less depressed, and have less seasonal allergy symptoms.

But, the problem with these cross-sectional, correlational studies is that you can’t prove cause and effect. Maybe seaweed consumption is just an indicator that they’re following “traditional Japanese dietary customs” in general, which have lots of different aspects that could protect against disease. To know for sure if seaweed could modulate immune function, you have to put it to the test.

So, typically, researchers start out like this: in vitro (meaning, like, in a test tube), which makes for quicker, cheaper, easier experiments. Take eight different types of seaweed, and basically make some seaweed tea you can drip on human immune system cells in a petri dish.

It was studies like these that showed that the seaweed wakame, which is what you find in seaweed salad, can quadruple the replication potential of T cells, which are an important part of our immune defense against viruses like herpes simplex virus. Yeah, but no one actually tried giving seaweed to people with herpes, until this study.

They gave people suffering from various herpes infections about two grams a day of pure powdered wakame, which is equivalent to about a quarter-cup of seaweed salad. And, “all fifteen patients with active Herpetic viral infections experienced significant lessening or disappearance of symptoms.” This included herpes virus 1, the cause of oral herpes, which causes cold sores; herpes virus 2, which causes genital herpes; herpes virus 4, also known as Epstein-Barr virus, which causes mono; and herpes 3, which causes shingles and chicken pox. There was no control group, though, but with no downsides, why not give it a try? Anyway, if you’re on a date, and they order seaweed salad, you might want to ask them about their history.

Researchers also found that wakame boosted antibody production. So, might it be useful to boost the efficacy of vaccines? The elderly are particularly vulnerable to suffering and dying from influenza. Now, the flu vaccine can help, but ironically, the elderly are less likely to benefit, because immune function tends to decline as we get older.

“It is hoped that the popular seaweeds eaten daily in Japan, though almost unknown” everywhere else outside of Japanese restaurants, will start to be more widely “consumed…for possible immunopotentiation boosting immunity and for attenuating the burden of infectious diseases in the elderly.”

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Thanks for listening to Nutrition Facts. I’m your host, Dr. Michael Greger.