In November 2013, the open access journal BMC Medicine carried an article by Canadian authors entitled ‘DNA barcoding detects contaminants and substitution in North American herbal products.’ In their abstract, the authors claimed that a survey of 44 herbal products representing 12 companies (sourced from the Toronto area) found:
• Most (59%) of the products tested contained DNA barcodes from plant species not listed on the labels
• Product substitution occurred in 30 of the 44 products
• Some of the contaminants found posed serious health risks
On the face of it, this looked like a major issue for the herbal industry and, needless to say, the media went in to its usual feeding frenzy. Articles were featured in the New York Times and USA Today. However, a close analysis of the study reveals a number of basic flaws, casting serious doubt on the findings of the study.
Misinformation sullies study results
The first key point is that none of the authors has any background or expertise in herbal quality control. This is clearly in evidence from the statement: “Currently there are no standards for authentication of herbal products.” Nothing could be further from the truth. The European, Chinese and United States Pharmacopoeias contain an extensive number of herbal monographs using a variety of state-of-the-art techniques such as chromatographic fingerprinting, key marker compound analysis and microscopic and macroscopic identification to authenticate herbs and herbal extracts. The authors didn’t even know that Health Canada regulates herbal products in their country, and that Canadian law requires herbal products to be made under pharmaceutical good manufacturing practice, the same standard used for drugs!
Absence of verification reveals a major study flaw
This lack of expertise underlies the major flaw in this study. A method such as the DNA barcoding of plants is in its relative infancy. It probably will be decades before it is incorporated into the herbal quality monographs in the above pharmacopoeias. Hence, if a problem with substitution was found, say as the authors claim with senna substituted for St John’s wort, it should have been verified by the known, validated techniques of identification above (but clearly unknown to the authors). For example, a relatively straightforward analysis of the product in question might have revealed the presence of sennosides, confirming the substitution. Any expert in the field of herbal quality control would know this is the essential next step to verify the DNA findings.
DNA barcoding without validation is misleading
The second key point is related to this: the science of DNA barcoding of plants is very new, so other techniques should have been used to validate the findings. With DNA barcoding there is still debate over which and how many points (or loci) in a plant’s DNA to use in order to reliably establish identity. Also, the computer programs used to compare the complex DNA patterns to see if they match are still in evolution. DNA can easily be damaged or lost by drying or extracting the plant. Fundamentally, DNA barcoding is not quantative. It might detect that a plant is present, but gives you no idea of how much. The following examples describe how this might lead to false conclusions in the absence of other verifying tests.
All the pharmacopoeias allow up to 1% foreign organic matter (from other plants) for herbs.
This is a normal consequence of harvesting a plant from a crop or the wild. Say the DNA of a particular plant is delicate and has been damaged, or does not respond well to the amplification method (PCR, polymerase chain reaction) used in DNA barcoding, however a minor contaminant present at less than 1% does respond. This will lead to the false conclusion that the herb has been substituted by this contaminant, when in fact this contaminant is only present at an insignificant level.
Trace contaminants can skew results
Another example might be where the herb has been added as an extract to the capsule and its entire DNA has been damaged or lost. The DNA amplification technique might instead pick up a very minor presence of another plant, perhaps as a trace contaminant in the extract carrier (herbal extracts are usually dried onto a carrier).
Again, this would look like an adulterated product, but it is nothing of the sort. DNA techniques are exquisitely sensitive, hence their huge value in crime scene analysis where the criminal might leave only a miniscule amount of their DNA.
Numerous inaccuracies and errors send up a red flag
The next key point is the authors have no knowledge of the herbal industry. In the key table of their findings (Table 1), they claimed to have tested readily available commercial products of wood sorrel (Oxalis corniculata), black-eyed Susan (Rudbeckia hirta) and thistle (Sonchus arvensis). In more than 30 years in the herbal profession, I have never seen commercial products from these herbs, and an internet search could find none. This is curious, to say the least. Again, a simple chemical test would have verified if this rather implausible substitution was real or not.
On the same key point, the authors confused Parthenium hysterophorus with feverfew (Tanacetum parthenium) in their safety discussion. Along the way, they greatly exaggerated the health risks of the latter to make their misguided point about the dangers of the former.
Some of the substitutions described are extremely unlikely and have never been noted before. One such example is black walnut for Ginkgo.
The final key point is that the paper is riddled with inaccuracies and errors beyond the examples above. For example, their abstract states product substitution occurred in 30 of the 44 products (68%), but in Figure 2 the number given is 32%. Perhaps they reversed the numbers, since 68 plus 32 equals 100%. One number is wrong, but either way such a basic error should have never gone uncorrected.
The REAL scandal is poor quality science
The DNA barcoding study into North American herb quality is indeed a scandal. But it is not one of a herbal industry needing to get its act together. Rather it is a scandal that the numerous oversights, inaccuracies, errors and misrepresentations in this study were not corrected at the peer review stage. It is also a scandal that the press gullibly took up this damaging and premature use of a new scientific method, completely ignoring a rational, factual perspective, even when it was offered by sane voices in the industry such as the American Botanical Council. Poor science should never receive this kind of media attention but unfortunately it seems to happen with an alarming regularity if the topic is herbs.
To your better health,
Nutrition & Healing
Vol. 8, Issue 2 – February 2014
Full references and citations for this article are available in the downloadable PDF version of the monthly Nutrition and Healing issue in which this article appears.