Revealing the widespread adulteration of commercial herbal medicines and food supplementsDNA barcoding and metabarcoding have substantially contributed to the authentication of herbal products and they hold the key to validated, DNA-based diagnostics for ingredient identification
The World Health Organization has estimated that up to 80% of the world’s population, especially in developing countries, rely on herbal medicinal products as a primary source of healthcare. Yet, these herbal products (HPs) – widely sold in food stores and supermarkets, as well as over the internet – are poorly regulated. By gathering and analyzing a dataset of a little less than 6,000 commercial HPs across 37 countries, this study found undeclared contaminant, substitute, and filler species, or none of the labelled species in more than a quarter of products thus highlighting the large-scale presence of herbal product adulteration across the globe.
Shelves with herbal products in a supermarket
PHOTO CREDIT: Mihael Cristin Ichim
Along with the tremendous increase in demand for both plant raw materials and processed HPs in the global marketplace, there has been growing scientific evidence of accidental contamination or intentional adulteration of commercial HPs. Irrespective of the authentication method used, the traditional pharmacopoeial (e.g., macroscopic and microscopic examination, chemical methods) or emerging DNA-based tools (e.g., DNA barcoding and metabarcoding), numerous studies have identified adulterants when the contents of commercial HPs were tested against their labelled ingredient species. But the scale of this phenomenon is unknown.
To understand whether herbal adulteration is a global phenomenon, I examined peer-reviewed scientific journals for studies on HP authentication that were based on detection methods using species-specific DNA sequences. By analyzing 5,957 commercial HPs, sold in 37 countries scattered across all continents, results revealed 27% of products contained undeclared contaminant, substitute, and filler species, or none of the labelled species. It is unclear whether these cases are accidental, or intentional and economically motivated.
Figure 1: The proportion of adulterated products (black) among continents.
The proportion of adulterated products varied significantly among continents, as high as 79% in Australia and as low as 23% in Asia (Figure 1). Of the countries with at least 100 products successfully authenticated and reported, the highest percentage of adulterated commercial HPs was found in Brazil (68%), followed distantly by Taiwan (32%), India (31%), and others (Figure 2).
All the commercial herbal products examined in this study were authenticated with DNA-based methods. These gradually advanced from classical molecular methods (e.g., Restriction Fragment Length Polymorphism) in early 2000 to DNA barcoding and metabarcoding in more recent years. The latter DNA barcoding methods were used to authenticate the majority of the reported commercial HPs, illustrating their growing utility as a tool to quantify rates of adulteration.
DNA barcoding – which makes use of short, standardized regions of the genome as species ‘barcodes’ – is a targeted approach suitable for the authentication of raw plant materials and the testing of single-ingredient HPs. Metabarcoding – a combination of high-throughput sequencing and DNA barcoding – enables untargeted, simultaneous multi-taxa identification by using DNA from different origins that can be extracted from more complex mixtures.
Besides the indisputable analytical advantages brought to herbal authentication, DNA barcoding and metabarcoding also have limitations. These are mainly derived from their high sensitivity to any amplifiable DNA extracted from the herbal product. Air-borne biological particles, such as pollen grains from neighbouring plants, can be deposited on the target plant and, when harvested, can be amplified, identified, and reported as adulterants of the finished herbal products rather than an accidental contamination. The ever-increasing analytical sensitivity of high-throughput DNA sequencing likely means that the proportion of adulterated HPs is expected to significantly increase.
It is important that the sensitivity of DNA-based authentication methods be optimized and effectively used to manage contaminated and adulterated HPs as they pose a significant risk for both the environment and human health. For example, often among the adulterants detected in commercial HPs are plant and animal species protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). More relevant to human health, HPs are often used in combination with conventional drugs. As HPs contain many pharmacologically active ingredients, the risk of adverse drug reactions – due to herb-drug interactions – increases when unknown, unlabeled plant ingredients are present in adulterated herbs taken with prescribed medications. Chronic, acute, and sometimes even lethal adverse health effects have been reported after the use of adulterated herbal products.
An accurate estimation of the adulteration of the HPs commercially available in the global marketplace is of paramount importance to all involved in their value chain, from growers, collectors, and producers, to pharmacists and medical practitioners, and finally, to the consumer.
Mihael Cristin Ichim
“Stejarul” Research Centre for Biological Sciences, National Institute of Research and Development for Biological Sciences, Piatra Neamt, Romania
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