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How have yams changed medicine?

By Chelsie Vandaveer

October 18, 2004

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The six hundred or so species of yams (Dioscorea Linnaeus) are warm-temperate to tropical plants. The genus is scattered about the globe—Africa, Asia, southern North America, and South America. The tubers of some of the species are edible and high in starch. Others are toxic containing saponins and sapogenins, yet have cultivars that are perfectly edible lacking the toxins. And some of the toxic species are edible if prepared properly, but these are usually considered 'famine foods'.

Plants from a Treatise by Dioscoride, 13th Century Giclee Print
Islamic School Buy Giclee Print at AllPosters.com

Linnaeus named the genus for Dioscorides [di os cor' i des], a Greek physician in the employ of the Roman army in the first century CE. During his travels with the army, Dioscorides set about collecting plants and their folk knowledge from the far reaches of the Roman Empire. His De Materia Medica would stand as the premier herbal for the next 1,500 years.

Yams have various folkloric uses and certainly Linnaeus had heard of a few. But naming the plants for Dioscorides was almost prophetic; little could Linnaeus guess how the yams, particularly Dioscorea terpinapensis and D. composita, would change medicine. It is the toxin diosgenin that has proved so useful in modern medicine.

Sultan Ahmet III with One of His Disciples, from "De Materia Medica" by Dioscorides Giclee Print Buy Giclee Print at AllPosters.com

The molecule of diosgenin has a 'backbone' of seventeen carbons arranged in three 6-carbon rings and a 5-carbon ring (6 of the carbons are shared). This base structure with various remainders (other atoms) attached are hormones and steroids found in human and animal physiology. Therapeutic hormones can be extracted from animals and cadavers, but the cost is prohibitive and would place treatment out of the range of most people.

Diosgenin chemically converted to cortisone and dihydrocortisone reduces inflammation due to arthritis or joint injuries. As a topical ointment, cortisone eases allergic reactions like insect stings and rashes. Converted to estrogen (female) or testosterone (male hormone), it provides hormone replacement therapy and aids in treating infertility. And as progesterone (female hormone), it can prevent a miscarriage or be taken for birth control.

Dioscorea bulbifera is one of the many toxic yams that have edible cultivars. Its bulbils are currently under investigation as to their feasibility for the extraction of diosgenin. To view a photograph of the "air potato", click on the link: http://www.killerplants.com/plant-of-the-week/20041004.asp

(Compiled from: The Merck Index, 11^th edition, Susan Budavari, editor, Merck and Co., Inc., Rahway, NJ, 1989 and "Studies on the Steroid Hormone Precursors of Two Tropical Wild Yams", G. Oboh, A.A. Akindahunsi and M.M. Ekperigin, United Nations Educational Scientific and Cultural Organization and the International Atomic Energy Agency, September 2001)

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