Some herbal supplements are being adulterated with plants not listed on the label, including top allergens like walnut, wheat and soy, according to a new study published in BMC Medicine.
“Herbal manufactures have not had easy access to DNA barcoding technology, so we should not expect them to know what is in the raw materials they are purchasing,” says Steven Newmaster, lead study author and botanical director of the Biodiversity Institute of Ontario at the University of Guelph, in Canada. DNA barcoding works by taking a “fingerprint” or barcode of the plant’s DNA, which is unique to each plant.
Researchers used DNA barcoding to analyze 44 North American herbal products, which are typically used to help alleviate a wide array of issues from poor memory to colds, depression and arthritis, and found that 59 percent contained plant species not listed on the label. Researchers compared the barcode derived from the herbal product with one derived from the known plant species to see if they matched. In many cases, they did not.
Some products were found to contain filler materials in addition to the plant matter they were supposed to contain, while others did not appear to contain the plant listed on the label at all.
Of significant concern for those living with food allergies or celiac disease, some herbal products were adulterated with top allergens: both soybean and wheat were found to be used as fillers. Yet exactly how much was present, whether it was protein (the allergenic part of a plant) and would cause a reaction was not examined.
In one case, black walnut was discovered in a Ginkgo product. The study authors believe, however, it is much more likely that leaves from walnut trees were unintentionally added, as opposed to walnut itself. They note that these leaves contain juglone, which has been shown to promote tumors.
The study authors stress that this was a small-scale study, and that it does not necessarily reflect the state of the natural health products industry as a whole. The study looked at fewer than 1 percent of the herbal products available on the market, from fewer than 5 percent of the companies that sell such products.
But scale aside, the significance of the findings is drawing media attention, including The New York Times . Another concerning contaminant was feverfew, an invasive weed from Europe and Asia, which can bring side effects like numbness of the mouth, oral ulcers, nausea and vomiting.
Feverfew can also trigger contact dermatitis and it can react negatively with certain medications, and pregnant women are never supposed to consume it. As well, a product labeled as St. John’s Wort, which is used to treat depression, was instead found to contain senna, a herbal laxative.
Next: Why the contamination?
It is difficult to determine exactly how the other plants made their way into the herbal products. It could be due to cross-contamination during processing, or it could be even be purposeful. “I suspect that the herbal industry is a victim of substitution and/or contamination in the supply chain,” Newmaster said in an interview with Allergic Living. “They purchase herbs just like consumers do, but at a larger scale.”
Since the plant matter is usually in a powdered or processed form, most manufacturers who buy large amounts of raw materials have no reliable way to verify what they’re purchasing.
The authors are not advocating the general public give up on herbal products – “there is a wealth of knowledge on the benefits of plant medicine,” says Newmaster, who has conducted research on the subject for 20 years.
Moving forward, he would like to see herbal products manufacturers embrace DNA barcoding technology to verify their products. In fact, he is working with his team to publish protocols for DNA barcoding, which commercial labs will be able to use to test foods or herbal products.
For those with severe food allergies or celiac disease who are using herbal products, there likely is no reason to stop if the specific brands aren’t causing any issues. (If you’re uncertain regarding symptoms, check with your doctor.) Concerns about a new product and how herbs are sourced should be directed to the manufacturer.
Unlike drugs, manufacturers don’t have to prove to the FDA that a herbal product is safe with clinical trials and study data; instead, the product must be proven unsafe to be in violation. Health Canada originally regulated herbal products as tightly as prescription drugs, but later switched to a system similar to that used in the U.S.
Read the full study here .