Arsenic in kelp supplements and one woman's illness
What it found
A woman who took kelp supplements daily developed memory loss, hair loss and other symptoms, and her urine arsenic was above normal.
After she stopped the supplements, her symptoms went away and her arsenic levels returned to normal.
What they found
Studies in people
Woman's symptoms and exposure
A 54-year-old woman had worsening hair loss and memory loss over two years, along with rash, fatigue, nausea and vomiting. She took kelp supplements daily, and a urine sample showed an arsenic level of 83.6 microg/g creatinine, above the normal limit of 50.
Arsenic in her supplement
A sample of the kelp supplement she took contained 8.5 mg/kg (ppm) arsenic. After she stopped the supplement, her symptoms resolved within weeks and her blood and urine arsenic became undetectable.
Other findings
Arsenic in other kelp supplements
Eight of nine kelp supplements bought from local health food stores had detectable arsenic, ranging from 1.59 to 65.5 ppm. Seven of the nine exceeded the FDA tolerance level of 2 ppm for certain food products.
Labels and contamination
None of the supplements had labels warning about possible arsenic or other heavy metal contamination.
What the authors conclude
“Our finding that eight of the nine commercially available kelp supplements contained detectable levels of arsenic is a cause for concern.”
Also in their conclusions
- They believe there was a causal link between the woman's kelp intake and her symptoms.
- They say it is prudent that companies demonstrate safety and efficacy before herbal products are placed on the market.
- They advise that clinicians should ask about dietary supplement use and be aware of possible heavy metal toxicity.
How it was done
The authors wanted to report a case of illness linked to arsenic in a herbal kelp supplement, and to check arsenic levels in other kelp supplements sold locally.
They described a 54-year-old woman who took a kelp supplement daily for about two years. They tested her urine and a sample of her supplement, and they bought nine kelp supplements from local health food stores and measured their arsenic levels.
What it can’t tell you
- This is a single case report, so it cannot prove that kelp supplements cause arsenic toxicity in other people.
- The authors could not identify any other exposure, but they note that the dose estimate was approximate.
Who paid
- Authors work at
- University of California-Davis, USA
The paper
- Title
- Case report: potential arsenic toxicosis secondary to herbal kelp supplement
- Type
- Case report
- Evidence
- Studies in people
- Summarised from
- Full text
- Licence
- Public domain. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Amster E, Tiwary A, Schenker MB (2007). Case report: potential arsenic toxicosis secondary to herbal kelp supplement. Environmental health perspectives. doi:10.1289/ehp.9495Free full textPubMed 17450231DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error