DNA Testing of Herbal Supplements Reveals Contamination, Substitution

The vitamin and herbal supplement industry takes in an estimated $5 billion a year in the US, and more than $60 billion worldwide. Until recently, herbs could only be identified using intact plants, not dried or powdered samples.

Recently, Canadian researchers looked at the DNA of 44 herbal products from 12 companies, representing 30 different species of herbs. According to their report published in the journal BMC Medicine, they randomly bought different brands of popular medicinal herbs from stores and outlets in the United States and Canada.

The intent was to get an overview of industry practices as a whole, so to avoid singling out specific companies they did not reveal the brand names or other details about the products tested.

More than half of the samples (59%) contained cheap fillers such as powdered rice, wheat or soybeans, as well as other plant species not listed on the label.

• Two products labeled St. John's wort -- which is typically taken to for depression and related symptoms like anxiety or trouble sleeping -- contained no St. John's wort. Instead, one product was filled with powdered rice. The other contained the powerful laxative Senna Alexandrina (fabaceae), an Egyptian yellow shrub that can cause chronic diarrhea, a cathartic colon, liver damage, abdominal pain and skin breakdown and blistering.
• A ginkgo product -- typically taken for memory loss, headaches or ringing in the ears -- was contaminated with black walnut leaves, possibly from nearby trees when the herb was harvested. In addition to being a problem for those with nut allergies, walnut leaves contain juglone, which is toxic and has been shown to promote skin tumors.
• Several bottles of Echinacea supplements -- typically used to fight colds and reduce infections -- contained only feverfew, an invasive Eurasian weed that has been used to treat fever, migraine headaches and arthritis. Feverfew's side effects can include swelling and numbness of the mouth, oral ulcers, nausea, vomiting, abdominal pain, diarrhea and flatulence, and some users experience withdrawal symptoms when they stop taking it.

"Contamination and substitution in herbal products present considerable health risks for consumers," said lead researcher Steven Newmaster, an integrative biology professor at the University of Guelph, in a statement about the study's results.

The researchers' report states it is a common industry practice to use fillers like rice, wheat or soybeans mixed with the active ingredients in a supplement, but in some cases the amount found indicates that the filler was used to replace most or all the active ingredient. Plus, the use of rice, wheat or soy fillers was not listed on the labels, which could cause problems for people allergic to those substances.

Unfortunately, although herbal supplements are regulated by the FDA, they are a separate category with rules that are much less stringent than those for drugs or foods. There is no industry-accepted standard for testing these products, and the DNA technique used in the Canadian study isn't considered fool-proof (it might not identify chemical extracts that don't contain plant material or products in which heat and processing has destroyed the original genetic material).

Consumers looking for more guidance in choosing herbal products may have to wait until additional research is done, and an industry-wide ingredient-testing standard developed. But this recent study does provide food for thought. Quality-control is a well-known problem in the herbal supplements industry, and needs to be addressed.

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