Definition: 

Several compounds exhibit a vitamin E activity : they are tocopherols. Alpha-tocopherol is both the most abundant and the most active, beta-tocopherol has only 30% of alpha-tocopherol activity, and gamma tocopherol has quite no vitamin E activity

One International Unit (IU) represents the activity of 1 mg dl-alpha-tocopherol. One alpha-tocopherol equivalent (TE) corresponds to the activity of 1 mg d-alpha tocopherol (more active than the dl form).

Conversion constants are :
1 TE = 1,49 IU
1 IU = 0,67 TE

Tocopherols are absorbed in the small intestine, only half of dietary intakes are actually absorbed. In blood plasma, tocopherols circulate in the High Density Lipoproteins (HDL) and Low Density Lipoproteins (LDL). This explains why blood tocopherol concentrations are strongly correlated to plasma lipids, and vitamin E levels should be expressed as ratios to lipid concentrations to detect possible deficiencies.

Fat tissues contain the major part of total body tocopherol.

Normal cell metabolism, and particularly cell respiration, produce very reactive molecules that have one or several unpaired electrons. These states are abnormal as a stable molecule should contain only an odd number of electrons. Every electron should be paired to another one that has opposite properties. As a free radical contain unpaired electrons, they combine quickly to surrounding molecules, doing that they become normal molecule, but the attacked molecules become free-radicals themselves and cannot play their physiological role any longer.

These deleterious effects may induce mutagenesis, cancerogenesis, and may accelerate ageing. Cholesterol deposition in arteries also involves oxidation and free radical mechanisms, and these depositions lead to artery occlusion, heart infarction, and blood intravascular coagulation

Alpha-tocopherol fights efficiently free radicals by transforming into tocopheryl-quinone. Its role is facilitated as it is dissolved in fats. Vitamin E is the most powerful extra cellular antioxidant.

Vitamin E stabilise cell membranes, this effect seem to be independent of its anti-oxidative properties. In vitamin E-deficient persons, red blood cells are more fragile and haemolysis is increased.

Vegetal oils are the most vitamin E-rich foods.

Recommended Daily Allowances :

Ten µmol/l is the threshold of vitamin E deficiency, however to protect against cholesterol deposition in arteries much higher concentration could be necessary. Certain authors consider that 30 µmol/l would be the right threshold

Vitamin E deficiencies are very rare in developed countries. They may occur in some digestive diseases that induce absorption or digestion insufficiency. In developing countries, vitamin E-deficiency is never isolated and is generally associated with global malnutrition states.