Do sea moss and carrageenan have health benefits? Are there risks?

Answer:

Sea moss (Chondrus crispus), also called Irish moss, is an edible red seaweed that grows along parts of the Atlantic coasts of Europe and North America, particularly along rocky shores. It is commonly used as a source of carrageenan, which makes up about 50% the dry weight of Irish moss. Carrageenan is used in foods and supplements to improve texture or as a thickening agent (Chopin, J Phycol 1995; Chopin, Botanica Marina 1999), although a specific type of carrageenan (sometimes called "poligeenan") has been linked with adverse health effects.

Sea moss (typically as a powder or gel) has been promoted for variety of health applications relating to thyroid health, Parkinson's disease, fertility, as well as to boost immunity and energy, improve gut health, to reduce pain, and improve skin and hair, but none of the purported health benefits of sea moss have been confirmed in clinical studies.

Read below for more details about the purported health benefits of sea moss, as well as information about possible side effects of sea moss and its constituent, carrageenan, when added to foods or supplements.

Sea moss

Purported health effects of sea moss
Thyroid health
Sea moss is a relatively good source of iodine, which is needed to make thyroid hormones. However, there do not appear to be any studies evaluating sea moss supplements for preventing or treating iodine deficiency or related thyroid conditions such as hypothyroidism (low thyroid activity).

Some sea moss powders, such as Organic Irish Sea Moss by The Food Movement, are labeled as containing about 40 mcg of iodine per 8 grams, which is only about 1/3 of the adult daily requirement (150 mcg). However, other powders such as Organic Sea Moss Powder by plnt contain as much as 140 mcg per 8 grams, and sea moss gel may contain 180 mcg of iodine per tablespoon (which is a typical suggested serving size for the gel). Although this is still below the Tolerable Upper Intake Level (UL) for adults (1,100 mcg), it is near the limit for children ages 1-3 (200 mcg) and 4-8 (300 mcg).

(Be aware that getting too much iodine can be problematic for people Graves’ disease and/or hyperthyroidism).

Boosting immunity
Sea moss is promoted as containing "free-radical-fighting antioxidants that support immune health." However, there do not appear to be any clinical studies to support this claim. While sea moss does contain some zinc, which has been shown to have direct antiviral effects and can help reduce cold symptoms when used as a lozenge, the amount of zinc in sea moss (about 0.2 mg per 2 tbsp or 10 grams), is much less than the amount shown to be beneficial for colds. An animal study showed that rats fed a diet that included sea moss had higher blood levels of immune antibodies (IgA and IgG) than those who did not consume sea moss (Liu, BMC Complement Altern Med 2015), but this possible benefit has not been confirmed in humans.

Improving gut health
Sea moss has been used traditionally "to soothe the digestive tract," but there do not appear to be any clinical studies evaluating sea moss for gut health in humans. Although sea moss has been shown to have prebiotic effects in animal research (Liu, BMC Complement Altern Med 2015), these effects have not been confirmed in humans.

Other uses
A retrospective study involving older adults (average age 63) with musculoskeletal complaints found that a greater number of those who took 500 mg of a sea moss supplement (BIO-ARCT® by Iontec S.A.R.L) enriched in the dipeptide L-citrullynin-L-arginine (2.8% to 4%) three times daily for 3 weeks reported less exhaustion/fatigue, less pain, and better mood compared to those who took the same sea moss supplement not enriched with the dipeptide (0.2%) (Palmieri, Asian J Med Sci 2018). However, this does not prove a benefit since there was no placebo-control.

In a worm model of Parkinson's disease, sea moss was been shown to have neuroprotective effects and decrease the accumulation of alpha-synuclein (a protein abundant in the brain that has been linked with Parkinson's disease, as well as Lewy body dementia) (Liu, Mar Drugs 2015), but there do not appear to be clinical studies evaluating sea moss for the prevention or treatment of Parkinson's disease in humans.

Sea moss is sometimes promoted for supporting fertility or improving hair and skin, but there does not appear to be any research supporting these claims.

Safety of sea moss

Some sea moss may contain trace amounts of shellfish and might cause allergic reactions in people with shellfish allergy.

Sea moss may cause gastrointestinal side effects in some people. In one study, involving 63 people, three cases of diarrhea and two cases of constipation were attributed to sea moss (Palmieri, Asian J Med Sci 2018).

Depending on where it is grown, sea moss can be contaminated with heavy metals, including arsenic, cadmium, and lead. Results of laboratory study of edible seaweeds found suggested that a typical daily serving of seaweed powder (8 grams) would contain about 6 mcg of cadmium and 6 mcg of lead (Besada, J Marine Syst 2009). These levels are above those the Prop 65 limits in California of 4.1 mcg of cadmium and 0.5 mcg of lead: Product that exceed these levels require a label warning possible reproductive harm and/or cancer. Even supplements containing suggesting smaller servings of sea moss may be required to include a Prop 65 warning.

As noted earlier, sea moss contains iodine. Although most suggested serving sizes of sea moss powders and gels do not appear to exceed to Tolerable Upper Intake Level (UL) for adults (1,100 mcg), some come close to the UL for children. Getting too much iodine can also cause thyrotoxicosis (a medical condition caused by high levels of thyroid hormone that, if severe, can cause a thyroid storm, which can be life-threatening). In one reported case, a 28-year-old woman with preexisting Graves' disease (which was not being treated with medication) was diagnosed with thyrotoxicosis (as well as pernicious anemia) after two years of intermittent use of a supplement containing Irish sea moss and bladderwrack (product name, dosage, and iodine content not disclosed). She experienced fatigue, anxiety, rapid heart rate, and weight loss, and tests showed she had elevated levels of free T4 (thyroxine) and very low levels of TSH. She was not given antithyroid medication, but one week after stopping sea moss supplementation her symptoms improved and her free T4 returned to within normal range, and TSH level increased (Khalifa, J Endocr Soc 2021).

Although just a single report, one case of liver injury resulting in elevated levels of bilirubin and liver enzymes has been reported in a 44-year-old woman in the U.S. who frequently consumed fruit smoothies made with sea moss from a local store. Her condition improved after she was treated in the hospital for several weeks (during which time she was also, presumably, not consuming these smoothies) (Chung, American College of Gastroenterology Poster 2023). However, it’s not clear from the report if other ingredients in the smoothie, medications, or other factors may have played a role.

Carrageenan

Carrageenan is used to create a smooth texture and thicken foods such as pudding, yogurt, ice-cream, whipped toppings, milk (including almond and soy milk), soups, and processed meats. Carrageenan is sometimes also added to supplements to improve texture or thicken ingredients. It can be found in some multivitamins, vegan and vegetarian sources of omega-3 fatty acids, such as algal oil supplements, nutrition bars and protein drinks. It has been estimated that people in Europe, Canada and the U.S. consume between 30 and 50 mg of carrageenan per day from foods (European Commission, Carrageenan 2003).

Food-grade vs. degraded carrageenan
The type of carrageenan approved for use as a food additive in the U.S. is called "undegraded" or food-grade carrageenan. This differs from the "degraded" form of carrageenan — sometimes called "poligeenan" — which is not approved for use in food (although it should be noted that food-grade carrageenan can contain small amounts of degraded carrageenan — one study found levels of degraded carrageenan in samples of food-grade carrageenan to be less than 5% (Uno, Food Addit and Contam 2001)). Food-grade carrageenan is also the form that is added to supplements, although you will only see it listed as "carrageenan" on the label.

Safety of carrageenan
Degraded carrageenan has been found to cause cancer, and inflammation and ulceration of the colon, when given in high doses to certain animals, and is considered to be "possibly carcinogenic in humans" by the International Agency for Research on Cancer, a division of the World Health Organization (IARC Monograph 2015, accessed from IARC Evaluation of Carcinogenic Risks to Humans). Food-grade carrageenan has not been found to cause cancer in animals. It is listed as GRAS (generally recognized as safe) by the FDA and is allowed in foods in amounts necessary for emulsifying, stabilizing or thickening (USDA 2011). Although this amount is not specified, food products may typically contain between 0.01% and 1% carrageenan (Stanley, Food and Agriculture Organization of the United Nations (FAO)). It does not pose a direct or indirect cancer risk to humans, according to the World Health Organization, which has also approved the use of carrageenan in baby formula (FAO/WHO 2014).

The European Commission (EU) concluded "there is no evidence of any adverse effects in humans from exposure to food-grade carrageenan, or that exposure to degraded carrageenan from use of food-grade carrageenan is occurring," but did propose limiting the amount of degraded carrageenan allowed in food-grade carrageenan to 5% (European Commission, Carrageenan 2003).

Studies have found food-grade carrageenan to cause ulcerations and damage to the lining of the intestine of some animals (but not others) (Tobacman, Environ Health Perspect 2001). This, in addition to research that found food-grade carrageenan to have adverse effects on human intestinal cells in-vitro (Tobacman, J Nutr 2008), has led to the concern that carrageenan in food could be harmful in people. In fact, the study's author, Joanne K. Tobacman, M.D., brought a citizen's petition to the FDA in 2008 to reconsider allowing food-grade carrageenan as a food additive. The FDA stated in its response that it had reviewed the evidence and found that the animal and in-vitro data did not accurately represent what happens when people ingest carrageenan from foods -- in the 2008 study, for example, human intestinal cells were directly exposed to carrageenan in a laboratory dish -- and upheld its position that carrageenan is safe for use in foods.

There has been little clinical research on the effects of carrageenan in people. However, a small placebo-controlled study in Chicago (involving Dr. Tobacman, noted above, and other researchers) found that carrageenan may contribute to earlier relapse of ulcerative colitis. In the study, 12 people with ulcerative colitis in remission were instructed to maintain a no-carrageenan diet, and half the group took capsules containing 200 mg of carrageenan daily (just under the average American adult daily intake of 250 mg) while the other half took a placebo. Within one year, three of the six people who took carrageenan experienced a relapse, compared to no relapses among those not given carrageenan. Furthermore, only the carrageenan group showed a statistically significant increase in interleukin-6, a measure of inflammation (Bhattacharyya Nutr Healthy Aging 2017).

Carrageenan can cause an allergic reaction in sensitive individuals (Tarlo, J Allergy Clin Immunol 1995; Nicklin, Food Addit Contam 1989).

The Bottom Line

Sea moss (typically as a powder or gel) is marketed for numerous conditions, but there does not appear to be good clinical evidence to support any of these uses. Sea moss may be contaminated with heavy metals and can provide excessive iodine to children.

Food-grade carrageenan does not appear to increase the risk of cancer and is likely safe when consumed at levels typically used in foods and supplements. However, if you suspect you have a sensitivity, notice gastrointestinal symptoms after consuming carrageenan, or have a condition such as ulcerative colitis, you may wish to avoid carrageenan. In its Product Reviews, ConsumerLab provides a full list of ingredients for each product so that people who want to avoid carrageenan can do so.

See the Review Article about Inactive Ingredients for more information about carrageenan and other ingredients commonly added to supplements.

Also see ConsumerLab.com's review of Seaweed Snacks and Foods.