Flavonoids are plant pigments that act as antioxidants, protecting the plant from the oxidative stress of photosynthesis. They act as antioxidants for humans who eat the plants as well. Silibinin is a flavonoid found in milk thistle. Flavonoids from milk thistle, like silibinin and silymarin have been shown to protect the liver from alcohol, drugs and poisons and to promote healing and recovery in the liver. According to a study appearing in the World Journal of Gastroenterology (2007 Oct 28:13(40):5299-305), silibinin protects against liver cancer. It reduces cancer cell proliferation and suppresses cancer cell progression. It also increases the programmed death of cancer cells (called apoptosis). Earlier studies [Current Medical Chemistry (2007:14(3):315-18) and Anticancer Research (2006 Nov-Dec:26(6B):4457-98)] have shown silibinin to be useful against a number of cancers, including cancers of the prostate, breast, ovary, colon, lung and bladder.

Research, appearing in the Journal of the National Cancer Institute (2006 Jun 21;98(12):846-55), shows that silibinin may inhibit lung cancer as well. The researchers injected mice with an substance that causes cancer. The mice were then divided into groups and given varying amounts of silibinin in their diets. After 18 weeks mice receiving silibinin had 38% fewer tumors than those that did not receive the flavonoid. At the end of 29 weeks, the supplemented mice had 70% fewer tumors than the controls.