Botanical Name / Family
Discorea composita, Discorea floribunda, Discorea mexicana, Discorea macrostachya, Discorea villosa (family Dioscoreaceae [yams])
Plant Part Used
Root and rhizome
The root of the wild yam contains diosgenin, dioscin, dioscorin and a range of vitamins and minerals such as vitamin C, beta carotene, vitamins B1, B2 and B3, iron, magnesium, potassium, selenium and zinc (US DA Phytochemical Database 2003) along with polyphenols. Although diosgenin can be converted to dihydroepiandosterone (DHEA) and other steroid compounds in the laboratory, and has been used for commercial production of these compounds, this conversion does not occur in the human body. Additionally, wild yam does not contain progesterone or any other active steroid hormones.
Wild yams have made a significant contribution as a root crop to tribal people in some parts of the world such as Nepal. Medicinally, wild yam has inaccurately been labelled ‘natural progesterone’. Although wild yam does not contain progesterone or other hormones, it is the source of diosgenin, the raw material originally used to produce progesterone in the laboratory. Its traditional use is primarily as an antispasmodic.
Wild yam: Main Actions
The evidence for a hormonal action of wild yam varies. Wild yam extract may enhance oestradiol binding to oestrogen receptors and induce transcription activity in oestrogen-responsive cells and diosgenin has been observed to have an oestrogenic action on mouse mammary epithelium. Alternatively, in an oestrogen competition assay using human breast cancer cell, diosgenin was found to cause an acute, endothelium-independent coronary artery relaxation, but did not interact with oestrogen or progesterone receptors and extracts with an upper limit of 3.5% diosgenin have been found to have no oestrogenic activity.
One study looking at steroid hormone-regulated gene expression using an in vitro tissue culture indicator system suggests that wild yam extract does not have significant oestrogenic or progesteronal activity, but rather weak anti-oestrogenic and/or anti-androgenic activities. A further study suggests that wild yam extract suppresses progesterone synthesis without direct effects on oestrogen or progesterone receptors. In an in vivo study, supplementation with diosgenin protected the kidney from morphological changes associated with ovariectomy and produced a significant decrease in the cortical and medullary adrenal areas of the ovariectomised rats.
There is in vitro evidence that diosgenin up-regulates vascular endothelial growth factor-A and promotes angiogenesis in preosteoblast-like cells via pathways involving oestrogen receptors.
There appears to be more consistent evidence for wild yam’s effect on bile flow. Diosgenin has been shown to increase biliary secretion of cholesterol and prevent oestrogen-induced bile flow suppression in rats, as well as increase elimination of indomethacin and reduce indomethacin-induced intestinal inflammation.