Kelp is a type of seaweed you'll see advertised as a weight-loss, cancer, diabetes and goiter remedy. Supplements also are sold to people seeking to boost antioxidant intake. As of 2010, there is some preliminary scientific evidence that looks promising for such uses, but no reliable studies in humans exist, according to the National Institutes of Health. NIH also advises that concerns about potential heavy metal contamination make taking kelp supplements "potentially unsafe."
Arsenic
Using kelp supplements may lead to inadvertent arsenic poisoning, say Eric Amster, Asheesh Tiwary and Marc B. Schenker in a case report published in "Environmental Health Perspectives." Reported symptoms include memory loss and alopecia, meaning hair loss, a rash, nausea, vomiting and increasing fatigue. Discontinuing the kelp supplements can resolve the issue, the authors note. Arsenic also can cause liver cancer, notes M. Rose, lead author for a study focusing on the amount of arsenic found in seaweed available to consumers. The study was published in "Food and Chemical Toxicology."
Mercury
Kelp supplements can be a source of mercury poisoning. Signs of chronic exposure to mercury include swelling, soreness, bleeding and ulceration of your gums and tongue, anemia, swelling known as edema and body wasting. Chronic mercury poisoning can cause degeneration of nerve tracts that lead to weakness, loss of coordination, blindness and coma, according to the Michigan Department of Natural Resources. One of the most famous cases of mercury poisoning was seen in the 1950s when residents of Minamata Bay in Japan contracted a progressive disorder of the central nervous system due to mercury-tainted foods from the sea. Symptoms of acute mercury poisoning include severe abdominal pains, diarrhea and vomiting.
Other Metals
The levels of cadmium, lead and selenium found in Alaskan kelp are at levels that suggest people who consume it may be at risk, says J. Burger, lead author for a study in "Environmental Health Perspectives." Metal poisoning from supplements usually takes a while to show up instead of having an immediate and dramatic effect, notes Patrick J. Walsh in his book "Oceans and Human Health: Risks and Remedies from the Sea." Other metals that can contaminate kelp include chromium and manganese, Burger notes.
References
- Medline Plus: Seaweed, kelp, bladderwrack (Fucus vesiculosus)
- "Oceans and Human Health: Risks and Remedies from the Sea;" Patrick J. Walsh; 2008
- PubMed: "Food and Chemical Toxicology"; Arsenic in seaweed--forms, concentration and dietary exposure; M. Rose et at.; 2007
- "Environmental Health Perspectives": Case Report: Potential Arsenic Toxicosis Secondary to Herbal Kelp Supplement; Eric Amster, Asheesh Tiwary and Marc B. Schenker; 2007
- PubMed: "Environmental Monitoring and Assessment"; Kelp as a bioindicator: does it matter which part of 5 m long plant is used for metal analysis?; J. Burger et al.; 2007
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