The naturally occurring forms of vitamin E are eight lipophilic molecules (as shown below), including α-, β-, γ-, and δ- tocopherols (αT, βT, γT, δT) and α-, β-, γ-, and δ- tocotrienols (αTE, βTE, γTE, δTE). αT is the only one of these eight compounds that is known to meet human dietary requirements. All of the vitamin E forms are absorbed in the small intestine, and then the liver metabolizes only αT. The liver then removes and excretes the remaining vitamin E forms (Vitamin E effects health).

As with all vitamins, the body cannot form vitamin E. It is only formed by the photosynthesis process of plants and therefore must be consumed in small quantities from external sources. Vitamin E deficiency is extremely rare in humans, as it is unlikely to be caused by a diet low in vitamin E; instead, it tends to be caused by irregularities in dietary fat absorption or metabolism. Premature infants also have low vitamin E reserves because vitamin E can only cross the placenta in small amounts.

Vitamin E functions as an antioxidant with activity in scavenging fat peroxide radicals and protecting cell membranes. Modulation of immune function by vitamin E also has clinical relevance as it affects host susceptibility to infectious diseases such as respiratory infections, in addition to allergic diseases such as asthma. Vitamin E may also play a role in reducing atherosclerosis and lowering the rates of ischemic heart disease.

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