α-Tocopherol

The most biologically active form of vitamin E, the form preferentially retained by the human body, a fat-soluble antioxidant that protects cell membranes and lipoproteins from lipid peroxidation. Rich sources include vegetable oils, nuts, seeds, and green leafy vegetables. In foods it serves double duty as nutrient and antioxidant additive, protecting fats and oils from rancidity and extending shelf life, which is why it appears on labels as E307. Deficiency is rare but causes neurological problems, while excessive supplementation has been questioned. Food scientists measure it to assess both nutritional value and oxidative stability, and its natural occurrence in vegetable oils partly explains their keeping quality.