Yucca extracts have traditionally been used by Native Americans for their medicinal qualities, particularly in supporting joint health. The Yucca schidigera plant contains a number of biologically active chemicals including steroidal saponins and polyphenols such as resveratrol.
Many of the medicinal effects of yucca are attributed to its saponin content. These phytosterols have been shown to bind to cholesterol in bile, increasing its excretion from the body and lowering blood levels. This action also accounts for the anti-parasitic action of yucca. By binding to cholesterol in the cell membranes of protazoa like Giardia lamblia, the saponins damage the cell membrane and eventually the protazoan cell dies. Yucca saponins have also been shown to have anti-bacterial properties and may support gut health by controlling overgrowth of bacteria.
There is some support for the traditional use of yucca for maintaining joint health as the polyphenols it contains are antioxidant and thus prevent tissue damage from free radicals (or reactive oxygen species (ROS)). They also inhibit Nuclear Factor kappa B (NFkB), an important immune system regulatory chemical that promotes inflammation. The polyphenol antioxidant resveratrol is widely known as a consituent of red wine and has been credited as a major contributor to the beverage's positive effects on cardiovascular health.
Finally, yucca extract has the ability to bind to ammonia, a toxic chemical by-product of the body's normal metabolism, as well as the metabolism of microorganisms, including the trillions of bacteria and other microbes that inhabit the human gut.
Cheeke PR Piacente S and Oleszek (2006) Anti-inflammatory and anti-arthritic effects of yucca schidigera: A review Journal of Inflammation 3(6)
Wallace RJ Arthaud L and Newbold CJ (1994) Influence of Yucca shidigera extract on ruminal ammonia concentrations and ruminal microorganisms Applied Environmental Microbiology 60(6):1762-7