Friday, 15 March 2019

Vitamin E: understand everything in 2 min

Vitamin E: understand everything in 2 min

Antioxidant effect

Most authors recommend a daily dosage ranging from 200 IU (134 mg) to 400 IU (268 mg) of natural vitamin E to be taken continuously.

Source: Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids, 2000. Food and Nutrition Board, Institute of Medicine. These data are the result of a consensus between Canadian and US authorities.
* The recommended nutritional intake is now given in milligrams. However, on supplements, the dosage of vitamin E is often indicated in international units (IU), an old measure. One milligram of alpha-tocopherol (the natural form of vitamin E) equals 1.5 IU.
** In the absence of sufficient scientific data, the authorities have established, not a recommended nutritional intake (RDA), but a sufficient intake (AS). Sufficient vitamin E intake was determined based on average intakes observed in healthy North American babies.

Description of vitamin E

Vitamin E plays a vital role in protecting the membrane of all cells in the body. It is antioxidant, that is to say, it contributes to the neutralization of free radicals in the body. In addition, it prevents or reduces the oxidation of low-density lipoproteins (LDL). This oxidation of LDL is associated with the appearance of atherosclerosis and therefore with cardiovascular diseases. 

Vitamin E also has anti-inflammatory, antiplatelet and vasodilator properties. These effects, which are not related to its antioxidant activity, also play a cardioprotective role.

Under the term of vitamin E, one group together 4 forms of tocopherols and 4 forms of tocotrienols. Of the 4 tocopherols, alpha-tocopherol is the most common form of vitamin E in the body. It is also the unit of measurement for the recommended dietary intakes and the vitamin E content of foods.

 Most supplements on the market contain alpha-tocopherol. The label "mixed tocopherols" indicates that the product contains, in addition to alpha-tocopherol, beta-tocopherol, gamma-tocopherol and delta-tocopherol, the other vitamin E compounds.

The body absorbs the natural form of vitamin E better than the synthetic form. There is controversy over the equivalence factor between these two forms2-3, but a consensus seems to have been established among the experts, around a ratio of 1.54-6. So, 400 IU of vitamin E in a natural form equivalent to 600 IU in synthetic form.

Some practitioners recommend using only supplements that come in a natural form rather than taking 1 ½ dose of synthetic supplements. The Other Names section, at the beginning of this leaflet, allows you to check the list of ingredients on the packages and to distinguish between natural source supplements and those containing synthetic tocopherols.

In fortified foods, it is usually synthetic vitamin E that is used by manufacturers.

Food sources of vitamin E

In general, nuts, seeds, vegetable oils and, to a lesser extent, green leafy vegetables are good sources of vitamin E. Note, however, that peanuts and pistachios contain less vitamin E than for example, almonds, hazelnuts, and sunflower seeds. However, to obtain therapeutic or preventive dosages (generally much higher than the ANR), the food is not suitable because it would consume large amounts of fat, vitamin E is mainly present in fatty foods.

Vitamin E deficiency

The risk of severe vitamin E deficiency is very low in developed countries. It is generally linked to diseases that cause fat absorption disorders (for example, cystic fibrosis, celiac disease and Crohn's disease). It is especially in the long term that symptoms of deficiency are manifested, usually by neurological problems attributable to poor nerve conduction.

On the other hand, the recommended dietary allowance (RDA) of vitamin E, which is set at 15 mg of alpha-tocopherol (the natural form) per day, would not be fully met by the diet of North Americans7,8. According to a survey conducted in the United States between 2001 and 2002, 

Americans would benefit from consuming significantly more seeds and nuts rich in vitamin E, such as almonds or sunflower seeds8, if they want ANR. This advice is probably valid for Quebeckers and Canadians, whose diet is similar to that of their neighbors to the south.

History of vitamin E

In 1922, Californian researchers discovered a fat-soluble substance in wheat germ and lettuce and named it "Factor X". They determined that this substance was essential for the reproductive function of rats. Factor X was then called vitamin E, then in 1936, tocopherol, a word from Greek (tokos: childbirth, race and wherein: porter) which recalled its importance for the reproductive system of animals.

In 2000, US and Canadian medical authorities significantly increased the recommended dietary intakes (RDA) of vitamin E from 10mg to 15mg per day for those over 149.

Vitamin E research

Effective, vitamin E?

Vitamin E has been the subject of a multitude of scientific research in recent years. For the moment, none has resulted in a clear demonstration of its therapeutic efficacy for a specific use.

This lack of clinical effects provokes ongoing controversy as the negative results of some long-term trials are published, the latter dating back to 2008 and 2009. Some evidence seemed more conclusive when vitamin E was associated with other antioxidants such as vitamin C, beta-carotene or selenium, but again, recent large-scale trials have been inconclusive12-14.

As a result of these inconclusive trials and their meta-analysis, several researchers have concluded that taking vitamin E, even in the long term, has no efficacy in preventing cardiovascular disease12,15 or cancer16,17, for example.

However, other researchers are questioning the negative conclusions of the clinical studies. They question whether the targeted populations, the type, and dosage of vitamin E used and the duration were adequate to detect the potential beneficial effects of vitamin E1,18-20,31,33.

Safe, vitamin E?

Some meta-analyses have questioned the safety of taking regular vitamin E at doses greater than 400 IU daily17,21,33. Although the statistical analysis of this work is criticizable22-24, some researchers believe that, in people with a normally low level of oxidative stress, taking high doses of vitamin E could lower this level below a critical threshold. and would then pose a health risk1.

Effectiveness of possible Menstrual problems. Vitamin E intake has shown positive but limited results in the treatment of menstrual-related disorders. Doses of 200 IU or 500 IU daily for 5 days, starting 2 days before menstruation, reduced the duration and intensity of menstrual pain in a group of adolescent girls27,28.

 Daily doses of 400 IU, administered according to the foregoing modalities, have also alleviated the symptoms of women with menstrual migraines99. Vitamin E may also relieve the symptoms of premenstrual syndrome25,26.