There are several active substances found in food called tocopherols, which are collectively known as vitamin E. Vitamin E is a fat-soluble compound sometimes referred to as the energy vitamin or d-alpha tocopherol. It was discovered in 1923 in California and was originally known as vitamin X, the anti-sterility vitamin or ‘the fertility vitamin’. These names reflect the early research into the link between vitamin E and the reproductive system.
Vitamin E describes tocopherols d-alpha, d-beta, d-gamma and d-delta, although there are others called tocotrienols.
The d-alpha tocopherol is the most potent of the group, being 100% biologically active. It is also more often found in natural oils, which is why it is often used as an alternative name for vitamin E.
Vitamin E or d-alpha tocopherol is a yellow oil, insoluble in water like vitamins A, D and K. Fat-soluble substances are transported in the body by fats and stored in fatty tissue, unlike water-soluble vitamins that are washed out of the system with aqueous fluids.
Vitamin E is stored in the body to be used when needed. The word tocopherol comes from the Greek word ‘Tokos’ meaning ‘birth’ and ‘Phero’ meaning ‘to bear’, the whole word meaning ‘to bring forth offspring’. This name and vitamins E’s subsequent reputation in the area of sexual fertility came about because of experiments on rats in the 1920s. Sterile rats became fertile when the diet was supplemented with foods that contained vitamin E.
Whilst vitamin E therapy has been controversial, having been concerned primarily with serious diseases, vitamin E is acknowledged throughout the world to be an important nutrient with major therapeutic uses, although all its functions in the body are not fully understood.
Vitamin E is measured in international units (IU) determined by biological activity and milligrams (mg) indicating weight. Potencies vary between the natural tocopherols prefixed by ‘d’ and the synthetic equivalent which are prefixed ‘dl’, for example 1mg of:
d-alpha-tocopherol = 1.49 IU
dl-alpha-tocopherol = 1.10 IU
d-alpha-tocopherol acetate = 1.36 IU
dl-alpha-tocopherol acetate = 1.00 IU
d-alpha-tocopherol succinate = 1.21 IU
dl-alpha-tocopherol succinate = 0.89 IU
This shows how much more biologically active the natural form is than the synthetic equivalents.
Tocopherols are widely distributed in food but the content varies. In food, vitamin E is always present in its natural state as free form tocopherols. Richest sources are cereal grain oils such as maize, corn and wheatgerm. Not all vegetable oils are good sources: coconut and olive oils contain very little of the nutrient.
Levels of tocopherols in cereal grain can vary according to the refinement process, time of harvest and storage conditions. These variations make it almost impossible to assess the vitamin E content of oil.
It should be noted that a balanced diet would include the four types of the tocopherol but in varying proportion. Examples of tocopherol content in some oils are:
|Tocopherol mg/per 100g||alpha||beta||gamma||delta|
Best natural food sources of vitamin E are:
- wholemeal bread, cereals
- eggs, milk, butter, margarine
- muscle meat, oily fish
- green leafed vegetables, pulses, fruit and root vegetables.
Fat-soluble vitamin E is absorbed from the gastrointestinal tract and is dependent on the presence of bile. It enters the blood stream via the lymph gland and is widely distributed in the cells. As much as several grams are stored in fatty tissues but most stays in the liver where it can be metabolised into an acid form and finally excreted in the urine. Vitamin E reaches its maximum activity 4 to 9 hours after ingestion, thereafter it is steadily excreted via bile and faeces.
Vitamin E is very sensitive to oxidation, particularly in the presence of heat and alkali. Freezing food devalues vitamin E considerably but the biggest losses of the vitamin result from processing and refining cereals.
Wholemeal bread contains 2.2 mg per 100 g compared to only 0.23 mg in the same amount of white bread. This is because the wheatgerm that contains vitamin E is removed during refining and the bleaching destroys any traces left.
Frying destroys 70 to 90% of the vitamin content in food, more if the fat or oil has been used several times. Boiling brings about 30% vitamin loss, so vegetables retain more of the vitamin if they are lightly cooked, steamed or braised. Cooking water can be reused for gravy to retain some of the lost nutrient.
Losses during food preparation are difficult to assess but it is estimated that about half the content is lost, i.e. a diet supplying 15 to 20 mg daily will only contribute 8 to 10 mg after cooking.
Vitamin E deficiency is unlikely to occur in people who are able to absorb fats and oils and a good balanced diet should provide sufficient to prevent health problems. Low levels of the tocopherols over a long period may produce deficiency symptoms that are not directly associated with a vitamin shortage. No clinical deficiency symptoms have been definitively established and most of the evidence available comes related to research with animals.
It is thought that without vitamin E the nervous system would be affected, muscular strength would be impaired, red blood cells may be endangered and anaemia may result.
The reproductive system is likely to suffer the greatest damage.
Clinical deficiency is acknowledged when certain conditions that affect absorption are present:
- intestinal disease
- cirrhosis of the liver
- obstructive jaundice
- cystic fibrosis
- coeliac disease
- following gastric or intestinal surgery
A water-soluble type of vitamin E is available in supplement form for those who cannot absorb the fat-soluble tocopherols from food.
Long-term use of liquid paraffin as used in some laxatives may also result in depletion of vitamin E levels.
In infants and premature babies haemolytic anaemia may occur because of low tocopherol levels. The condition responds rapidly to supplementation of vitamin E.
The true measures of a deficiency can only be ascertained by medical investigation, i.e.
- low blood levels of the vitamin
- increased fragility of cells
- increased creatine in the urine
- haemolytic anaemia
- deposition of brown or yellow fat
Nutritionists are, however, aware of the potential danger to health posed by marginal deficiency, resulting from an inadequate diet. Modern diets containing processed and junk food can be totally lacking in this important vitamin. A 12mg (16 iu) recommended daily amount (RDA) is suggested for minimal health requirements.
Vitamin E is closely linked in metabolism with selenium and the two nutrients appear to be interdependent. The mineral appears to mimic vitamin E in some of its actions and so when selenium intake rises, less vitamin E is require
One of the most important functions of vitamin E is as a protector of other essential nutrients such as:
- vitamin A
- vitamin C
- polyunsaturated fatty acids
- amino acids cystine, cysteine and methionine
All of these compounds can be destroyed by oxygen unless tocopherols are present.
It is generally thought that iron interrupts the functioning of vitamin E and this is true in the ferric form. In its ferrous form, however, it is accepted by the vitamin. When taking an iron supplement, it is better to use the amino acid chelated mineral to prevent the possibility of the element being converted to a ferric form by food constituents.