One antioxidant that occurs in nature is vitamin C (ascorbic acid), which is contained in many citrus fruits and acerola (17% of the fruit). Other natural antioxidants belong to the vitamin E family and are provided primarily in nuts and kernels. Tocotrienols, which also belong to the vitamin E family, have been shown in vitro to have an antioxidative effect up to 40 times stronger than α-tocopherol. Other natural protective substances, for example, Rutin with antioxidative properties include polyphenols (especially in red wine), flavonoids (wine, tea, fruit, and vegetables), phytoestrogens and protease inhibitors.