Supplement Quality and Concerns
The most clinically tested form of gingko is Ginkgo biloba extract (GBE) as opposed to whole leaf powder. GBE contains two major groups of phytochemicals, or marker compounds: flavonol glycosides and terpene lactones. Extracts shown to work in clinical trials contain at least 22% glycosides and 5% terpene lactones.
Ginkgo biloba is thought to have been one of the most adulterated herbal supplements, meaning ginkgo products were frequently contaminated with other, less expensive substances that contain these marker compounds. For example, some manufacturers have used a small amount of ginkgo extract and added flavonol glycosides from less expensive buckwheat.
Independent testing of ginkgo supplements has shown a number of products to lack expected levels of flavonol glycosides and terpene lactones. In 2003, tests conducted by ConsumerLab.com found seven of 9 popular ginkgo supplements did not contain expected levels of marker compounds. In 2006, six of 13 products failed testing for the same reason (two of which also contained high levels of lead per daily serving- 12 and 16 mcg, respectively). Five of eight popular supplements tested also failed ConsumerLab.com testing in 2008, one of which was contaminated with lead.
Tests in 2012, however, suggested the quality of ginkgo supplements may be improving. Of four popular ginkgo supplements selected for testing by ConsumerLab.com, three contained adequate marker compound levels and none failed for unacceptable levels of lead.
Read more about this topic: Ginkgo Biloba
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