In my last post, I gave an overview on the basics of botanical research. To compile meaningful information you frame your question, structure your inquiry, search the appropriate databases, store and organize your information for easy access, and understand that you have to interpret the information. This last step is the hardest part.
After you’ve completed your literature search, you’ll want to look at the quality and nature of the information in front of you. The best way to assess the strength of the evidence is to know the research methods that were used–and their limitations.
In vitro studies
In vitro means ‘in glass’, and describes laboratory research conducted on cells or molecules outside of their biological environment. It is the least expensive and easiest type of research to conduct in comparison to other methods. It’s therefore used in bioprospecting and pharmaceutical screenings. Often, a group of researchers hear of a traditional use of a particular plant and that’s their clue to investigate its biological activity starting in vitro or in animals. These are also known as mechanism of action studies, as studying those cells up close can shed light on how particular herbs or compound are affecting certain cells.
In vitro studies usually test isolates or purified extracts. Sometimes, as in the case of oncology bioprospecting at the National Cancer Institute, important compounds like tannins are removed (Mills & Bone 2013). Tannins bind nonspecifically to many proteins and enzymes, and the removal of them drastically changes their biological activity. These purified extracts or compounds are added to a culture medium and incubated with cells, and changes are noted and documented. This brings us to a serious drawback of in vitro data: the difficulty of extrapolation.
For example, a 1999 in vitro study tested the effects of several botanical extracts (Echinacea, Ginkgo biloba, Saw palmetto, and St. John’s wort) on fertility. To do this, they cultured hamster oocytes (eggs) with pretty high concentrations of these extracts (upwards of 0.6mg/mL) and then tested sperm penetration (Ondrizek et al 1999). When you’re reading a study or abstract, try to envision what’s actually going on. Is it relevant? For reference, concentrations above 0.1mg/mL are unlikely to be achieved in people taking herbs orally.
Furthermore, and more troubling, is that you can’t get product preparation or extraction details from an abstract or even a full text sometimes. I’m consistently surprised to see how often authors neglect to describe the extract type (aqueous or ethanolic? Crude herb?). This is especially prolific in the mushroom literature, where extraction methods are crucial yet strangely absent from the abstracts.
In vitro data should be carefully examined before conclusions are made. Again, this is usually Step 1 in the process of seeing if a particular herb merits further study. Read more