It should be stated upfront that the wild yam is not the same as the common American “sweet potato.”1 More than 600 species of wild yam have been identified, but only 12 are known to be edible.2

In some areas of the world, these edible species are grown as dietary staples. One, Dioscorea villosa—otherwise known as the Mexican wild yam — is a tuberous plant that produces a thick, starchy underground rhizome. It is this root that is used in many herbal remedies — in both nutritional and medicinal products.2

Background

The wild yam is marketed as an herbal remedy for menstrual discomfort and menopausal symptoms, and is typically promoted as an alternative to hormone replacement therapy (HRT).

In the two years since the publication of the Women’s Health Initiative (WHI) — a study designed to address the most common causes of death, disability and impaired quality of life in postmenopausal women — women have increasingly turned to natural alternatives to patented estrogens.3 Survey findings recently released by the Stanford School of Medicine indicated that the number of prescriptions written for HRT in postmenopausal women dropped by more than 50% from pre-WHI levels.4,5 This suggests that a very large number of postmenopausal women are now seeking alternative methods for controlling hormonal decline.

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The wild yam seems like a natural solution, as it contains diosgenin, a steroid that can be used to synthesize various hormones — estrogen, dehydroepiandrosterone (DHEA) and progesterone — in the laboratory.6 Yet while a small number of animal studies have demonstrated in vivo synthesis and hormone surge, studies in humans have not successfully replicated this process.6

Diosgenin, extracted from the tubers of Dioscorea villosa, has been promoted as a natural form of DHEA, yet the chemical reaction needed to convert diosgenin into DHEA is not known to occur in the human body. Ingesting the yam extract has not been found to increase DHEA levels in humans.

Science

A standardized, evidence-based rating system showed poor efficacy scores for the wild yam, indicating fair scientific evidence against its use for alleviating menopausal symptoms.7

In a small, double-blind, placebo-controlled trial, researchers studied 23 healthy women with postmenopausal symptoms. After a four-week baseline period, each subject was given topical wild yam extract (a cream typically used to ameliorate hot flashes) and matching placebo for three months in random order.8 Diaries were completed for the baseline period and for one week each month thereafter. Blood and saliva samples were collected at baseline and at three and six months to measure lipid and hormone levels.8

The diaries showed no significant difference between the two groups, with no real change from baseline for either group.8 This suggests that short-term treatment with topical wild yam extract has little effect on menopausal symptoms.

A study examining hormone levels in Taiwanese postmenopausal women after yam extract ingestion did not show appreciable changes in serum concentrations.2 In this trial, 24 women replaced their daily dietary staple of rice with a wild yam supplement for thirty days.2 At one month, serum concentrations of estrone (a weak form of estrogen) increased 26% in the cohort, with sex-hormone-binding globulin levels up nearly 10%, and data showed a lesser increase in serum estradiol (the principal form of estrogen produced by the ovaries).2 It should be noted that estrone is typically seen in postmenopausal women who are not on HRT, and its potency is far less than estradiol.9

Safety, interactions

Trials of topical and oral preparations showed no significant adverse effects. However, large doses of wild yam extract can cause nausea, vomiting, and diarrhea. Women who are pregnant or breastfeeding should not use wild yam derivatives. Allergic reactions, although rare, can occur; they typically include rash and respiratory distress.10

Many manufacturers add synthetic progesterones to wild yam products. Although not advertised as having additives, consumers should be cautious since many products may be adulterated.

Dosage and cost

Wild yam is available in a variety of forms, but topical creams and powder-filled capsules are the most commonly used. Depending on the concentration of the product, the recommended dose is one teaspoonful of cream applied twice daily or 250 mg of wild yam powder, taken one to three times daily. Cost varies depending on the source and formulation.

Summary

The use of wild yam as a substitute for commercially available HRT is not evidence-based, but it is relatively benign. Patients wanting to try wild yam can be counseled that it is safe but not proven to be efficacious. In patients with other clinical conditions and/or additional circumstances involving estrogen levels, a more involved discussion should take place.

References

1. Tufts Medical Center resources page: Wild Yam. Tufts Medical Center website.

2. Wu WH, Liu LY, Chung CJ, et al. Estrogenic effect of yam ingestion in healthy postmenopausal women. J Am Coll Nutr. 2005;24:235-243.

3. Women’s Health Initiative page. National Institutes of Health website.

4. School of Medicine news release. Stanford School of Medicine website.

5. Wegienka G, Havstad S, Kelsey J. Menopausal hormone therapy in a health maintenance organization before and after Women’s Health Initiative hormone trials termination. J Womens Health. 2006;15:369-378.

6. About Herbs, Botanicals, & Other Products page. Memorial Sloan-Kettering Cancer Center website.

7. Ulbricht C, Basch E, Sollars D, et al. Wild yam (Dioscoreaceae). J Herb Pharmacother. 2003;3:77-91.

8. Komesaroff PA, Black CV, Cable V, Sudhir, K. Effects of wild yam extract on menopausal symptoms, lipids and sex hormones in healthy menopausal women. Climacteric. 2001;4:144-150.

9. Therapeutic Research page. Natural Medicines Comprehensive Database website.

10. Herbs, Vitamins, and Minerals information page. American Cancer Society website.

All electronic documents accessed on January 31, 2012.

From the February 01, 2012 Issue of Clinical Advisor