UC Davis study finds high arsenic levels in herbal kelp supplements

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The woman's symptoms had begun with minor memory loss and fatigue. Her primary care physician initially found nothing wrong with the woman and thought the symptoms were related to menopause. With no specific diagnosis or treatment recommendations, the patient started taking a variety of herbal therapies, including a kelp supplement, fish oil, ginkgo biloba and grape seed extract. The kelp supplement was the only herbal therapy she took regularly throughout the course of her illness.

Over a period of several months the woman's short- and long-term memory became so impaired that she could no longer remember her home address. She also reported having a rash, nausea and vomiting, which made it very difficult to work and forced her to leave a full-time job. The woman actually increased her dosage of kelp from two to four pills a day after her doctors still could not find a clear diagnosis.

Subsequent laboratory tests finally revealed arsenic in the patient's blood and urine. At her physician's suggestion, the patient discontinued the kelp supplement. Within weeks, her symptoms disappeared, and within several months arsenic was no longer detected in her urine and its levels had dropped significantly in her blood. She later was referred to the UC Davis Occupational Medicine Clinic as a follow-up to her primary care.

"It's unfortunate that a therapy that's advertised as contributing to 'vital living and well-being' would contain potentially unsafe levels of arsenic," said Schenker, who is a professor of Public Health Sciences and a leading authority on occupational and environmental diseases and respiratory illness. "Concentrations of materials contained in herbal supplements, including both the expected benefits and potential side effects, should be studied, standardized, monitored and accurately labeled."

To assess the concentration of arsenic present in commercially available kelp supplements, the UC Davis investigators purchased nine over-the-counter kelp samples from local health food stores. Included were samples from three different batches of the product consumed by the patient.

The researchers sent the samples to the California Animal Health & Food Safety Laboratory in Davis, which operates in partnership with UC Davis, the California Department of Food and Agriculture and others to provide specialized testing that helps protect both human and animal health. Investigators found detectable levels of arsenic in eight of the nine kelp supplements by using a hydride vapor generation method with an inductively coupled argon plasma spectrometer. Seven of the supplements exceeded the tolerance levels for food products set by the U.S. Food and Drug Administration (FDA).

"Part of the problem," said Schenker, "is that the FDA has limited control over dietary supplements. It can't scrutinize products like herbal kelp before they enter the market, so it has to rely on adverse reports to determine product safety."

He noted that none of the kelp products in the study had labels indicating the presence of arsenic, nor were there any warnings about the potential dangers of ingesting large quantities of the supplement.

Arsenic is a heavy metal that occurs naturally in the environment and as a by-product of some agricultural and industrial activities. Due to high arsenic concentrations in algae and marine micro-organisms, seafood is the highest dietary source of arsenic for consumers. While long-term human exposure to arsenic from food sources such as fish does occur, it is usually significantly lower than anything approaching toxic levels. How-ever, dietary supplements, which are largely unregulated, have raised health concerns.

There have been a number of published studies highlighting cases in which the uses of homeopathic remedies to relieve everything from asthma to rheumatoid arthritis have caused arsenic poisoning. Schenker's findings offer a cautionary tale for consumers who use herbal treatments and dietary supplements. The kelp samples analyzed in the study had consistently elevated levels of arsenic, but they were considerably lower than previously documented concentrations found in other herbal remedies.

"What concerns me," said Schenker, "is that chronic exposure to contaminated herbal supplements, even those with moderately elevated concentrations of arsenic, can still be toxic. Consumers won't find such label information on these products, so they could end up like that woman in our study who consumed dangerously high amounts of a toxic substance without realizing it."

University of California, Davis-Health System