Ginkgo: yes or no? Maybe.
Why this particular tree and not another? What’s so special about Ginkgo? It’s an old, old tree, from the evolutionary point of view, a relic of the times when plants didn’t yet have flowers. Even its leaves are “old”, primitive, resembling those of the very primitive ferns, like Adiantum. The leaves of Ginkgo, unique among seed plants, are fan-shaped with veins radiating out into the leaf blade, sometimes splitting, but never fusing to form a network. No flowers, no fruit, those things that look like fruits are actually seeds covered by a fleshy layer of tissue. A very primitive tree indeed and it’s remarkable that it has survived almost unchanged for millions of years.
Ginkgo has a magical aura (note: this is not a scientific term) because it’s such an unusual tree. It doesn’t follow, though, that it’s beneficial for humans as a source of medicinal substances. The leaves extract of Ginkgo may be promoted as a dietary supplement for many conditions, including anxiety, allergies, dementia, eye problems, peripheral artery disease, tinnitus, etc. We know better, right? At least we should. Incidentally, sales of Ginkgo extract just in the USA are about 100 million dollars per year.
We can look at the chemicals the extract contains and see whether such a wide list of benefits is even possible. And be aware that there are other parts of the tree that may also be commercialized as medicinal extracts. The internal part of the seed and the fleshy tissue that covers the seed have different chemical compositions between them and from the leaf. Is any of these worth it? Are the claims supported by research?
Despite the beauty of the tree, Ginkgo starts with a big handicap as a candidate for medicinal use: it contains toxic substances. This means that unless there is a fantastic, special chemical in it that can be separated from the toxic ones, there is no point in using it.
What are the beneficial components? Flavonol glycosides, terpene lactones, and ginkgolic acids. Extracts from different suppliers vary a lot and can’t be relied on to contain a high content of these beneficial chemicals. flavonoids, glycosylated quercetin, kaempferol, and isorhamnetin are the most abundant.
What are those toxic components? The neurotoxic compound 4′-O-methylpyridoxine (MPN, also known as ginkgotoxin) and MPN glucoside in ginkgo seeds. MPN is chemically related to vitamin B6 and interferes with its biosynthesis, metabolism, and function. MPN inhibits the formation of 4-aminobutyric acid (GABA) from glutamate, involved in transmitting nerve signals from one nerve cell to another. The dual effect of a decrease in GABA and an increase in glutamate is believed to induce seizures and convulsions. Cooking cannot inactivate MPN although it may reduce the toxicity of the seeds, probably by inactivating cyanogenic glycosides.
Also, raw ginkgo seeds contain toxic cyanogenic glycosides, dangerous even by touch. Despite this, ginkgo seeds are used for food in some countries, especially in times of food scarcity like in Japan after World War II.
What about the leaves? Ginkgo biloba leaf extract has been classified as a possible human carcinogen (Group 2B) by the International Agency for Research on Cancer. Although the leaves contain very little toxic MPN, their extract can cause bleeding.
Ginkgo products contain more than 70 chemical components, several of them toxic. My suggestion? Find the “good stuff” in other natural sources or, if possible, get them pure, so that you don’t have to worry about all the undesirable components. I say “no” to Ginkgo, except in art and as decorative tress.
References
Ren, Q., Chen, J., Ding, Y., Chen, J., Yang, S., Ding, Z., … Ding, Z. (2018). In vitro antioxidant and immunostimulating activities of polysaccharides from Ginkgo biloba leaves. International Journal of Biological Macromolecules. doi:10.1016/j.ijbiomac.2018.11.276