Both oils also contain dense amounts of tocopherols, tocotrienols and plant sterols. Natural antioxidants include ascorbic acid (vitamin C) and tocopherols (vitamin E). Scientists have suggested tocotrienols are better antioxidants than tocopherols. The oil contains high concentrations of oleic acid, tocopherols, and carotenoids, especially beta-carotene. Poppy seeds are especially high in tocopherols other than vitamin E (alpha-tocopherol). Some mixed tocopherols with higher gamma-tocopherol content are marketed as "High Gamma-Tocopherol". For example, vitamin E consists of four tocopherols and four tocotrienols. Vitamin E exists in eight different forms, four tocopherols and four tocotrienols. Also present are tocopherols and tocotrienols (two types of vitamin E) and phytosterols. Like cholesterol, carotenoids and tocopherols are transported by lipoproteins. The side chain is attached (saturated for tocopherols, polyunsaturated for tocotrienols). Some brands may contain 200% w/w or more of the other tocopherols and measurable tocotrienols. During the 1990s, the anti-cancer properties of tocopherols and tocotrienols began to be delineated. It is also the precursor to carotenoids, gibberellins, tocopherols, and chlorophylls. The seeds also contain beneficial antioxidants, such as tocopherols, which are thought to fight cancer.