Claims for benefits of yams are on the wild side
The Irish Times
Health Supplement, p. 13
28 April 2009
WILD YAMS have gained a reputation for treating symptoms of premenstrual syndrome (PMS). Medical research in 2002 raised concerns about side effects of hormone replacement therapy for menopausal symptoms. Interest in “natural alternatives” to pharmaceutical steroid hormones grew rapidly, with wild yams becoming popular in liquid preparations and as creams.
The connection between wild yams and steroid hormones is not new. Up until the 1940s, female hormones like oestrogen and progesterone had to be obtained from natural sources – primarily animal glands and urine. Intense research developed as part of the war effort due to a rumour that Nazi pilots were being injected with steroids to allow them to fly higher on bombing missions. It was later found to be nothing more than a rumour, but the research led to a steroid that effectively relieved arthritis pain and stiffness.
With the growing realisation of the value of steroids as drugs, plentiful sources were needed. Plants were known to contain steroid-like substances, and a search was launched to find ways to chemically convert these into the desired steroids. An American chemist working in Mexico found that wild yams contained a particularly good starting material called diosgenin. Via a small number of chemical reactions, diosgenin can be converted into many of the different steroids needed. Production increased rapidly and, within a few years, the price of progesterone went from $1,000 to $1 per gram. This led to widespread study and marketing of steroids, which have gone on to be the most widely used class of drugs in medical history.
The current renewed interest in wild yams is hoped to avert the problematic side effects of the semi-synthetic steroids. In addition, wild yams themselves are known to contain a variety of steroid-like substances. However, about 600 different species of wild yam exist, each containing a different mixture of steroid-like substances. The effects of each will most likely vary also.
Evidence from studies
A small number of laboratory studies have found that wild yam extracts and cream have oestrogen-like effects. The precise mechanism of these effects is not known.
Only one study of a wild yam cream in humans was located. Twenty-three women with menopausal symptoms were randomly assigned to either wild yam cream or a placebo cream. After three months, the women using the wild yam cream were no better than those using the placebo. No adverse effects were reported in either group.
Some wild yam products also claim to be a natural source of DHEA. This steroid hormone is produced in humans, but its production decreases with age. Some have claimed that the problems of ageing are connected to reduced DHEA levels and, therefore, that by taking DHEA we can remain youthful. Other wild yam products claim to contain no DHEA.
All of the claims about wild yam as a source of natural steroids suffer from one major problem. When diosgenin is isolated from wild yam, a few chemical reactions must be carried out to make the required hormones for use in pharmaceuticals. Those reactions do not occur in the human body, so there is no known way for us to convert diosgenin into the required steroids. While wild yam may contain other compounds that might be beneficial in women’s health, none have been isolated to date. Currently, no controlled evidence exists to support the use of wild yam creams or extracts.