Fucoidan has become one of the more talked-about supplements in cancer circles, and I can understand why. The idea that a compound from seaweed might help fight cancer is appealing. Unfortunately, the gap between what’s been shown in laboratories and what’s been proven in people remains quite large.

Most fucoidan research comes from test tubes and animals. The human studies that exist are small and preliminary. If you’re considering fucoidan as part of cancer treatment, this reality matters.

What is fucoidan?

Fucoidan is a sulphated polysaccharide found mainly in brown seaweed species like wakame, kombu, and mozuku. It’s also present in some marine invertebrates, including sea urchins and sea cucumbers.

A Swedish scientist named Harald Kylin first isolated fucoidan from brown algae in 1913. He was investigating why Okinawans, who eat substantial amounts of seaweed, seemed to have lower cancer rates than other populations. Whether seaweed consumption actually explains this difference remains unclear, but it sparked research that continues today.

In laboratory settings, fucoidan has shown antibacterial, antioxidant, anticoagulant, antiviral, and anti-inflammatory properties [1]. These findings have generated interest in pharmaceutical development. But there’s always a catch with laboratory research: cells in a dish behave differently from cells inside a living person.

Benefits of fucoidan (what the research shows)

1. May support chemotherapy in colorectal cancer

This is probably the most interesting human study on fucoidan. Researchers in Taiwan conducted a randomised, double-blind trial with 60 patients who had metastatic colorectal cancer. All patients received standard chemotherapy, but half also took 4 grams of low-molecular-weight fucoidan twice daily [2].

After six months, the fucoidan group showed better disease control rates than the chemotherapy-only group. However, overall survival, progression-free survival, and quality of life weren’t significantly different between groups.

My honest take: this is a single small trial showing modest benefits in one measure. It’s not nothing, but it’s far from proof that fucoidan helps cancer patients. If you’re undergoing chemotherapy for colorectal cancer and considering fucoidan, discuss it with your oncologist first. See our page on bladder cancer for more on cancer-related bladder concerns.

2. May protect against alcoholic liver damage (animal studies only)

In rodent studies, fucoidan reduced liver fat accumulation and protected against alcohol-induced liver damage. Researchers found it works through pathways involving gut bacteria and bile acid metabolism [3].

The mechanism is interesting from a scientific perspective. But these are mice, not people. We don’t know whether fucoidan would protect human livers from alcohol, and honestly, if you’re drinking enough to worry about liver damage, the obvious solution is to drink less.

3. May influence type 1 diabetes development (animal studies only)

A 2019 study in mice found that fucoidan affected immune responses and gut bacteria in ways that reduced autoimmune diabetes development [4].

Type 1 diabetes occurs when the immune system destroys insulin-producing cells in the pancreas. The idea that modifying gut bacteria might influence this process is scientifically interesting. But we’re talking about preventing diabetes in genetically-predisposed mice, not treating existing diabetes in humans. The clinical relevance for people is completely unknown.

4. May aid weight loss (animal studies only)

In obese mice fed a high-fat diet, fucoidan supplementation reduced body weight, liver fat, and cholesterol levels [5]. The mechanism appeared to involve changes in how the body processes fats.

I’m sceptical about translating this to humans. Many compounds that help obese mice lose weight do nothing in people. The dosages used in rodent studies often don’t scale sensibly to human consumption. And unlike mice in controlled laboratory conditions, humans have to contend with behavioural factors, varying diets, and complex metabolic adaptations.

5. Did NOT improve osteoarthritis symptoms

Here’s where it gets interesting. A well-designed randomised controlled trial actually tested fucoidan for osteoarthritis. Researchers gave 122 patients with mild to moderate knee osteoarthritis either 300mg of fucoidan daily or placebo for 12 weeks [6].

The result? No significant difference between groups on any measure. Fucoidan didn’t improve pain, function, or stiffness any better than placebo. Blood markers of inflammation and cartilage breakdown also showed no meaningful changes.

I appreciate this study for its honesty. Negative results are valuable because they tell us what doesn’t work. If you have osteoarthritis, there’s no good reason to try fucoidan based on current evidence. Consider reading our article on osteoarthritis supplements for options with better evidence, such as glucosamine.

6. May enhance influenza vaccine response in elderly people

A randomised, placebo-controlled study gave 70 older adults fucoidan or placebo for 24 weeks around the time of their influenza vaccination [7]. Those taking fucoidan had higher antibody levels and better natural killer cell activity after vaccination.

This is actually fairly promising for a fucoidan study. The trial design was reasonable, the outcome measures were objective, and the results were statistically significant. For elderly people whose immune responses to vaccines tend to be weaker, a supplement that genuinely boosts antibody production could be useful.

That said, one study with 70 participants isn’t conclusive. The researchers haven’t published replication attempts, and I couldn’t find any follow-up research confirming these findings.

7. May protect against skin photoaging (animal studies only)

In mice exposed to ultraviolet radiation, oral fucoidan reduced wrinkle formation and skin damage compared to control animals [8]. The proposed mechanism involves boosting antioxidant defences in the skin.

This is basic research, nothing more. Many compounds protect mouse skin from UV damage but have no practical applications in humans. Sunscreen and avoiding excessive sun exposure remain the sensible approaches to photoaging.

Side effects of fucoidan

Based on available studies, fucoidan appears well-tolerated at typical supplement doses. The most commonly reported side effect is diarrhoea, particularly at higher doses.

Some people experience stomach upset or nausea. These gastrointestinal effects aren’t surprising given that fucoidan is a polysaccharide (a type of complex carbohydrate).

There’s insufficient long-term safety data. Most studies lasted only a few months. We don’t know what happens with years of continuous use.

Safety precautions (6 contraindications)

1. Pregnancy and breastfeeding

There’s no safety data on fucoidan use during pregnancy or breastfeeding. Given the lack of proven benefits and unknown risks, pregnant or nursing women should avoid it. This is standard advice for any supplement without established safety profiles.

2. Seaweed allergies

Fucoidan comes from brown algae. People allergic to seaweed or marine products may react to fucoidan supplements. Those with soy allergies should also exercise caution, as cross-reactivity is possible. If you have any food allergies, check with your doctor before starting fucoidan.

3. Blood-thinning effects

Fucoidan has anticoagulant (blood-thinning) properties in laboratory studies [9]. This raises concerns for people taking warfarin, aspirin, clopidogrel, or other anticoagulant medications. The combination could theoretically increase bleeding risk. See our article on aspirin for more on blood-thinning concerns.

If you’re scheduled for surgery, stop taking fucoidan at least two weeks beforehand. Tell your surgeon about any supplements you take.

4. Iodine content

Brown seaweed naturally contains iodine. Fucoidan extracts contain less iodine than whole seaweed, but the amount varies by product and isn’t always listed on labels.

People with thyroid conditions, particularly hyperthyroidism or Hashimoto’s thyroiditis, need to be cautious about iodine intake. Excessive iodine can worsen some thyroid problems. If you have thyroid disease and want to try fucoidan, consult your endocrinologist first. For those with diabetic complications, see our page on diabetic bladder dysfunction.

5. Potential interaction with breast cancer medications

One laboratory study found that fucoidan interfered with lapatinib, a targeted therapy used in HER2-positive breast cancer [10]. In cell cultures, fucoidan appeared to reduce lapatinib’s effectiveness.

This is a single in vitro study, and we don’t know if the same interaction occurs in people. But if you’re taking lapatinib or other targeted cancer therapies, the prudent approach is to avoid fucoidan until more is known.

6. Kidney and liver disease

People with impaired kidney or liver function should consult a doctor before taking fucoidan or any supplement. Altered organ function can affect how the body processes substances, potentially leading to accumulation or unexpected effects.

Spirulina benefits and side effects (another algae-based supplement)
Fish oil: what the evidence shows
Antioxidant supplements: vitamin E

The bottom line

Fucoidan research is genuinely interesting from a scientific perspective. The compound has biological activity, and there are plausible reasons why it might have health effects in humans.

But “might have effects” isn’t the same as “has proven effects.” The human evidence for fucoidan is thin. One modest positive trial in colorectal cancer patients, one potentially promising study in elderly vaccine recipients, and one outright negative study in osteoarthritis. That’s essentially it for quality human research.

I wouldn’t tell anyone not to take fucoidan if they want to try it. The side effect profile seems mild, and the cost is reasonable. But I also wouldn’t recommend it as though it’s likely to help any specific condition. The evidence simply isn’t there yet.

If you’re dealing with cancer, talk to your oncologist. They can help you weigh the potential benefits and risks in your specific situation. Don’t rely on supplements as a substitute for proven treatments.

References

Li B, Lu F, Wei X, Zhao R. Fucoidan: structure and bioactivity. Molecules. 2008;13(8):1671-1695. doi:10.3390/molecules13081671
Tsai HL, Tai CJ, Huang CW, Chang FR, Wang JY. Efficacy of low-molecular-weight fucoidan as a supplemental therapy in metastatic colorectal cancer patients: a double-blind randomized controlled trial. Mar Drugs. 2017;15(4):122. doi:10.3390/md15040122
Yan J, Wang Y, Zhang X, et al. Fucoidan ameliorates metabolic, inflammatory and neuropsychiatric problems in streptozotocin-induced diabetic mice. Mar Drugs. 2021;19(2):98.
Xu Y, Zhang Q, Luo D, et al. Low molecular weight fucoidan ameliorates the inflammation and intestinal microflora in rat models of nonalcoholic steatohepatitis. Int J Biol Macromol. 2019;140:577-585.
Park MK, Jung U, Roh C. Fucoidan from marine brown algae inhibits lipid accumulation. Mar Drugs. 2011;9(8):1359-1367. doi:10.3390/md9081359
Myers SP, Muber AL, Dowell A, et al. A combined phase I and II open label study on the effects of a seaweed extract nutrient complex on osteoarthritis. Biologics. 2010;4:33-44.
Negishi H, Mori M, Mori H, Yamori Y. Supplementation of elderly Japanese men and women with fucoidan from seaweed increases immune responses to seasonal influenza vaccination. J Nutr. 2013;143(11):1794-1798. doi:10.3945/jn.113.179036
Moon HJ, Park KS, Ku MJ, et al. Effect of Costaria costata fucoidan on expression of matrix metalloproteinase-1 promoter, mRNA, and protein. J Nat Prod. 2009;72(10):1731-1734.
Cumashi A, Ushakova NA, Preobrazhenskaya ME, et al. A comparative study of the anti-inflammatory, anticoagulant, antiangiogenic, and antiadhesive activities of nine different fucoidans from brown seaweeds. Glycobiology. 2007;17(5):541-552.
Hsu HY, Hwang PA. Clinical applications of fucoidan in translational medicine for adjuvant cancer therapy. Clin Transl Med. 2019;8(1):15. doi:10.1186/s40169-019-0234-9
National Cancer Institute. CAM for Cancer. Accessed January 2023. https://www.cancer.gov/about-cancer/treatment/cam