Side Effects of Fucoidan

Fucoidan -- an extract from brown seaweed -- is currently available in supplemental tablets. It causes few side effects, but it can interact with anticoagulant medications. If you take this type of prescription medication to prevent blood clots, don't take fucoidan unless it's under the supervision of your doctor. When you buy supplements, check the label for proof of quality assurance, such as a USP Verified Mark, and look for info telling you where the seaweed came from to be sure it's not contaminated with radioactive waste.

Fucoidan is a sugar naturally found in brown seaweeds. (Image: vau902/iStock/Getty Images)

About Fucoidan

The structural difference between the simple and complex carbs found in food comes down to size. Both are made from single units of sugar, but simple carbs contain one to several sugar molecules, while complex carbs -- called polysaccharides -- have thousands of sugar molecules. The same idea applies to fucoidan. It's also a large polysaccharide made from lots of smaller units of a sugar called fucose.

Your body synthesizes fucose, then uses it to make substances such as hormones and enzymes, which fill a lot of roles in the body including regulating cellular communication. Fucoidan is easily extracted from its primary natural source -- brown seaweed -- and used to make supplements or concentrated for research studies. In laboratory studies, fucoidan inhibits inflammation and kills cancer- and disease-causing cells. It also boosts the immune system and works as an antioxidant that stops unstable molecules called free radicals before they can cause nerve damage, according to studies cited by Memorial Sloan Kettering Cancer Center.

Side Effects, Drug Interactions, Overall Safety

If you eat seaweed, the fucoidan you'll consume is considered safe and not likely to cause side effects. In supplemental form, fucoidan may cause diarrhea, but it should improve as soon as you stop taking the supplement. Fucoidan is a dietary fiber, so if you experience bloating or diarrhea, fiber could be the culprit. While all fucoidan contains fucose, it also contains a variety of other chemical components depending on the type of brown seaweed. Some fucoidan contains xylose or mannose, sugars known to cause diarrhea.

A more serious concern arises if you take anticoagulants such as warfarin and heparin, which slow down blood-clotting. Fucoidan also affects blood-clotting and may increase your risk of bleeding if you take it while you're also on anticoagulants, reports Memorial Sloan Kettering Cancer Center. As researchers continue to study fucoidan, new side effects may be discovered, but so far it's considered nontoxic.

Concerns About Radioactive Contamination

Following the Fukushima nuclear reactor disaster in Japan in March 2011, seaweed became contaminated with radioactive fallout. Levels of contamination fell in the two years following the disaster, but seaweed still had measurable levels. Tanks full of radioactive waste remain on the site, and experts believe they continue to leak waste into the ocean.

While some scientists say the levels of contamination aren't high enough now to pose a risk to people, make sure you know where your fucoidan comes from. The label should report the seaweed's origin. If it doesn't, look for another brand. An article published in Life Extension Magazine in September 2015 recommends buying supplements made from seaweed harvested from the southeastern coast of Argentina, off the shore of Patagonia.

One species of brown seaweed often used to produce supplements is Undaria pinnatifida, but it's not the only option. Other rich sources of fucoidan that you may find on supplement labels include the brown algae species Laminaria and Fucus.

Promising Research and Potential Uses

Currently, fucoidans are primarily used in dietary supplements. While significantly more research must be done before approval for medical use, studies show some promising benefits. In lab mice, it reduced inflammation in the colon, the hallmark of bowel diseases such as ulcerative colitis and Crohn's disease, reported PLoS One in June 2015. Another study published in October 2015 in the scientific journal Inflammation reported that fucoidan may one day be used to treat rheumatoid arthritis because it inhibited the growth of cells that stimulate this debilitating joint disease.

Other research focuses on fucoidan's ability to kill cancer cells and stop cancer from spreading, reported a review in the April 2015 issue of Marine Drugs. It may even help relieve side effects associated with chemotherapy. In a small study, researchers treated 10 chemotherapy patients diagnosed with advanced or recurrent colorectal cancer with fucoidan. They were able to tolerate chemotherapy longer and experienced less fatigue than a second group of patients who didn't take fucoidan, according to Oncology Letters in March 2011.