The predominant action of vitamin E is that of regulating the oxidation processes of the body. This anti-oxidant action links vitamin E with vitamin A metabolism (it is used for the stabilization of vitamin A in foodstuffs), and with that the unsaturated fatty acids. It prevents or slows down the formation of free radicals and hyper peroxides from poly-saturated fatty acids. The decrease in peroxide formation can be considered as a stabilizing effect on cell membranes, containing poly-saturated fatty acids. Selenium is a trace element, reducing tissue peroxides and stimulating immunity response. Interaction with vitamin E is sometimes synergistic and sometimes partially substitutive.