Kelp: The Oceanic Plant With Skin, Health & Thyroid Benefits

When you think of kelp, you probably think of slimy green seaweed. Maybe you imagine it grazing your leg in the ocean and sending chills down your spine. Maybe you've never encountered it IRL and you think of it more as scenery dancing around Ariel in The Little Mermaid. Either way, there's a good chance you don't think about purposefully putting it in or on your body—but maybe you should.

Kelp, which is the large, brown algae you may have seen in the ocean (or, at least, in pictures of the ocean), is a natural source of some key minerals and vitamins our bodies need and boasts potential benefits ranging from cancer treatment to weight loss aid and anti-aging properties for the skin.

Kelp, as we explained before, is a kind of large brown algae. You might know kelp by its more colloquial moniker: seaweed. There are at least 30 different kinds of kelp, all of which grow in saltwater (so, primarily oceans) and thrive in cool, relatively shallow waters close to the shore. You won't often find just a little kelp, either. It grows in dense, forestlike groupings known, appropriately, as kelp forests.

If you're looking for kelp in the wild, you're going to want to look in cold, shallow, nutrient-rich saltwater close to shore. Kelp needs light for photosynthesis, so kelp forests are rarely found deeper than 49 to 131 feet. What's more, kelp needs a hard surface (read: not sand) to grow.

It's found around the world, but the Pacific Coast of the United States and Canada is particularly dominated by it—with 100,000 to 170,000 tons harvested each year from California waters alone.

Kelp isn't just in the oceans, though. You've almost certainly encountered it, in some form or another, in the course of your normal, land-based life. Did you miss it? That's OK, you're not alone. Kelp is also found in many products and foods we consume daily, like toothpaste and ice cream. This is because algae (like kelp) is very versatile. Algae known as diatoms, which have hard, glasslike shells made of organic compounds and silica, are useful as micro-abrasives, which makes them perfect for things like water filtration systems, natural cleaners, and, yeah, even toothpaste.

Kelp is one of the best natural sources of iodine1, which is essential to thyroid hormone production. This is important because an iodine deficiency can lead to a goiter—an enlargement of the thyroid gland—or to metabolism disruption (which could lead to a thyroid disorder, causing things like weight changes and high cholesterol2). Too much iodine can also be a problem, though, and can cause many of the same problems3 as consuming too little iodine, including goiters, thyroid gland inflammation, and even thyroid cancer.

"The recommended daily intake1 of iodine is 150 mcg for healthy adults, but if you're pregnant or breastfeeding, your needs are higher (220 mcg and 290 mcg)," registered dietitian and nutritionist Jess Cording, M.S., R.D., CDN, told mbg. "While iodine deficiency is pretty rare in the U.S., if you don't regularly consume iodized salt or are on a vegan diet, you may need to be more mindful to work iodine-rich foods into your regular diet. Seaweed is a great example of a plant-based food source. Just be mindful that too much of a good thing is also possible, so don't stress about trying to incorporate it at every meal! Even a few servings a week can give you a boost."

Kelp is also an excellent source of vitamin K, vitamin A, vitamin B-12, calcium, iron, and magnesium. Here's why you need those things (because, seriously, they're all important): Vitamin K4 aids with bone metabolism and helps produce the protein that's key to blood clots. Vitamin A5 is key to so many functions in your body, from making sure you have normal vision to aiding the immune system, and in reproduction. At the same time, it also helps the heart, lungs, kidneys, and other organs work properly.

Vitamin B-126 helps boost the metabolism and give you more energy. Calcium7, as we all know from those old Got Milk? commercials, is important in maintaining strong bones but is also needed for our heart, muscles, and nerves to function properly. "Kelp is often called a 'superfood from the sea' because it has 10 times more calcium than milk and more vitamin C than OJ," said Robin Berzin, M.D., founder of Parsley Health. "While kelp contains dozens of essential vitamins and minerals, it's difficult to find kelp on the menu and get it into one's daily diet—which is one of the reasons I'm excited for AKUA's Kelp Jerky and all the new kelp snacks we are seeing on the market," she told mbg.

Iron8 is important for growth and development in the body and is famously the substance our body needs to create hemoglobin, the protein that lets red blood cells carry oxygen from the lungs to the rest of the body. Finally, magnesium9 is important in helping to regulate muscle and nerve function, blood sugar levels, and blood pressure in the body, as well as making protein, bone, and DNA.

While kelp is a great source of all of the above vitamins and nutrients, its real claim to fame nutritionally is as a source of calcium—it's a better source than most vegetables, including kale.

Kelp also has potential therapeutic uses; it has been shown to help slow the spread of colon and breast cancers. It could also potentially help mitigate the spread of lung and prostate cancers, thanks to fucoidan, a compound found in kelp.

There's also a chance that kelp could aid in weight loss. The brown algae contains a natural fiber called alginate, which studies have found can block fat absorption in the gut by 75 percent. As a result, kelp is being researched as a weight loss supplement that could be added to foods like yogurt. It's also been studied for its effects on diabetes and obesity and, when combined with pomegranate oil, could help promote weight loss for obese patients. Studies suggest kelp could also help lower blood glucose levels, which could make it a great treatment for people with type 2 diabetes.

Beyond use as a supplement or potential medicine, kelp could be the key to a long and happy life. It's a dietary staple in Japan (different kinds of kelp account for a staggering 21 percent of Japanese meals10), and it's been suggested that this could be a contributing factor in Japanese people's above-average life spans.

If you're seriously considering increasing your kelp intake at this point, know that kelp supplements come in powder or capsule form. While both forms are effective ways to increase the amount of kelp (and all the vitamins and nutrients it carries) in your diet, in general, powder forms of supplements are more absorbable (and can also be mixed into drinks, which is a plus).

Kelp supplements can carry serious risks, and some have been found11 to contain high arsenic levels. Other analysis12 has suggested that arsenic-related issues with kelp supplements have been due to users taking more than the recommended dosage and say that the arsenic in kelp is organic and less toxic13 than the inorganic variety, but it's still a concerning fact about the highly nutritious seaweed.

Because it's such a strong source of iodine, kelp supplements are not recommended for people with hyperthyroidism.

By now, it should be clear that most research suggests kelp is pretty great to put into your body. But overachieving kelp is also a great thing to put on your body—or at least on your skin. Brown algae has many benefits for skin14. It's high in antioxidants14 and also acts as an anti-inflammatory, meaning it will help reduce redness in the skin. In addition to reducing inflammation and redness, kelp is also a powerful moisturizer and could even have anti-aging effects.

Carrageenan is an additive that can be used to thicken, emulsify, and preserve foods and drinks. It's often associated and sometimes even confused with kelp, but carrageenan comes from red seaweed. Kelp is brown seaweed, so carrageenan definitely isn't kelp.

Carrageenan has been controversial since the 1960s, thanks to evidence that it can trigger inflammation and ulcers and can damage the digestive system. Some studies show that it can promote or cause inflammation, bloating, irritable bowel syndrome, glucose intolerance, colon cancer, and food allergies.

Perhaps carrageenan's most harmful attribute is its known tendency to cause inflammation (roughly 3,855 research papers show this effect of carrageenan, which is often used in studies that test the effectiveness of anti-inflammatory drugs). This might seem like a relatively minor side effect, but prolonged inflammation can often lead to more serious diseases, including cancer.

Food-grade and degraded carrageenan have been shown in studies15 to be more or less the same. This is a problem, since degraded carrageenan is a carcinogenic, unapproved version of the seaweed—and definitely not something you want to put in your body.