Terpenes are a diverse chemical group of lipid soluble compounds found in plants that is made up of around 30,000 members. Examples include ginkgolides in ginkgo biloba, valerenic acid from Valeriana officialis and ginsenosides from Panax ginseng. They are formed via the mevalonate and deoxy-d-xylulose pathways in all living organisms, but are a particularly important group in plants. Structurally, they contain 1 or more 5-carbon isoprene units, with the number of isoprene units determining the group name. Hemiterpene, monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes and teraterpenes have 1, 2, 3, 4, 5, 6, and 8 isoprene units, respectively. Terpenes in plants are used for a number of functions including antimicrobial properties, as toxins to predators, and also play a role in altering the behaviour of some insects via interaction with their central nervous systems.
However, while terpenes can be detrimental to insects they appear to be of low toxicity to mammals, can add to the flavour of many herbs and spices, and in some case have beneficial medicinal properties. Gingko biloba leaf extracts have been used medicinally for a number of millennia in humans and have been shown to have beneficial effects on health. Terpenes within Gingko biloba leafs include gingkolides A, B, C and J as well as a range of flavonoid glycosides. The contents of these active ingredients within the plant are used as anti-microbials and as predator deterrents, and their concentrations are increased by environmental stress on the plant. In humans, the same compounds can decrease platelet activation and increase nitric oxide availability with the result of improved cerebral and peripheral blood flow.
Because of the ability to increase cerebral and peripheral blood flow, Ginkgo biloba has been researched extensively for its ability to prevent or improve various forms of dementia. A meta-analysis of 29 studies suggested that the effects that Ginkgo biloba has on dementia is promising and that chronic supplementation with Gingko biloba extract resulted in improvements in attention, executive function and long-term memory. As well as its beneficial effects on blood flow, Gingko biloba may also possess in vivo antioxidant functions on account of the presence of flavonoid glycosides. Evidence suggests that supplementation with leaf extracts may alter a number of neurotransmitter systems through inhibition of monoamine oxidase A. This action may explain some of the benefits seen in dementia. Cognition may also be improved following acute doses in otherwise healthy individuals, as has been reported in a number of trials.
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