Vitamin E: Sources, Recommended Intake, and Functions

Introduction

Vitamin E is a group of fat-soluble compounds having antioxidant properties important for health. Evans and the Bishops discovered these in 1922. These are called tocochromanols, categorized as tocopherols and tocotrienols, showing the biological activity of d-alpha-tocopherol. Vitamin E occurs in eight natural forms alpha, beta, gamma, delta tocopherols, and alpha, beta, gamma, and delta tocotrienols, mainly synthesized by plants. The two primary forms of vitamin E are alpha-tocopherols and gamma-tocopherols, found in the serum and the red blood cells, while alpha-tocopherols are in higher concentration. In the plasma, delta and gamma tocopherols are present in lower concentrations. In humans, alpha-tocopherols have a faster metabolism than other tocopherols because of the binding affinity of alpha-tocopherols with alpha-tocopherol transfer protein (TPP). Alpha-tocopherol is secreted in urine, while beta, gamma, and delta-tocopherols are secreted in bile which gets excreted in the urine. It mainly acts as an antioxidant to prevent cell damage from free radicals.

What Is the Chemistry of Vitamin E?

The tocopherols are methyl substitutes of tocol with a saturated side chain, while the tocotrienols have an unsaturated side chain. Both of the compounds have a similar chemical structure. There is a chromanol ring in which position number 2 gets occupied by an isoprenoid side chain in tocochromanols. The RRR- configuration is seen in natural tocopherols, while in synthetic ones, eight different isomers are seen, thus known as all- rac- alpha-tocopherol. Tocotrienols show chiral recognition as they have a chiral center at the C-2 position.

What Are the Sources of Vitamin E?

Plant-based oils like nuts, seeds, fruits, and vegetable oils are the primary sources of vitamin E, listed below as:

• Wheat germ oil.

• Soybean oil.

• Sunflower oil.

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• Corn oil.

• Peanuts.

• Peanut butter.

• Broccoli.

• Spinach.

• Tomatoes.

• Mango.

• Kiwi.

• Green leafy vegetables.

As it is a fat-soluble vitamin, it gets stored within the fat cells of humans. Thus these need not be consumed every day.

What Is the Recommended Intake of Vitamin E?

About 15 mg daily vitamin E intake is recommended for humans above the age of 14 years. The recommended dietary allowance for pregnant women is the same, but those who are lactating need to take higher amounts, like around 19 mg daily.

What Are the Functions of Vitamin E?

Vitamin E is vital in preventing cardiovascular diseases, cataracts, Alzheimer's disease, cancer, and HIV/ AIDS. Meanwhile, it helps protect cell membranes, preventing illnesses related to reactive oxygen species, regulating platelet aggregation, etc.

• Vitamin E as an Antioxidant - The reactive oxygen species formed during the oxidation of fats and free radical reactions. Still, vitamin E, an antioxidant, suppresses the formation of reactive oxygen species. As vitamin E (mainly alpha-tocopherol) is present in cell membranes, it dramatically protects the cell from being damaged by the effects of free radicals. In comparison, some of the existing free radicals get neutralized by gamma-tocopherol.

• Repair of Plasma Membrane- Vitamin E helps in the protection of the plasma membrane by inhibiting the generation of oxidized phospholipids. These membrane phospholipids are affected by the oxidants, and lipid peroxidation is thus efficiently prevented. For such processes to take place, alpha-tocopherols are required, and in the absence of alpha-tocopherols, plasma membranes cannot be repaired.

• Activation of Protein Kinase - Alpha-tocopherol has an attenuating effect on the formation of diacylglycerol, a lipid that helps in the translocation of protein kinase C activity. It is due to the RRR configuration of alpha-tocopherol. It also enhances the activity of protein phosphatase type- 2, decreasing the phosphorylation of protein kinase C. There occurs inhibition of platelet aggregation due to the effect of tocopherols.

• Disease Prevention - Vitamin E plays a vital role in anti-inflammatory processes, platelet aggregation inhibiting processes, and immunity enhancer due to its acting as an antioxidant, thus proving to be effective in the prevention of many diseases.

What Is the Relation Between Vitamin E and Human Health?

• Cardiovascular Diseases - The oxidation of low-density lipoproteins is mainly responsible for many cardiovascular diseases following the resultant inflammation. Gamma-tocopherols enhance the activity of nitric oxide synthase, which is responsible for producing nitric oxide. Nitric oxide helps the vessel dilate and thus improves cardiovascular functions. Studies show that regular doses of 100 mg gamma-tocopherols reduce platelet aggregation and cholesterol accumulation in humans. Tocotrienols also decrease the production of cholesterol. Some studies contradict this fact and show that the use of vitamin E is responsible for hemorrhagic stroke.

• Cancer - Anti-cancer properties are also exhibited by vitamin E as it helps in the stimulation of p53 tumor suppressor genes, the downregulation of the mutant p53 protein, and the activation of heat shock proteins. Vitamin E molecules show different responses towards cancer as alpha-tocopherol suppresses the production of collagenase and protein kinase C, promoting cancer cell growth. Gamma and delta-tocopherols inhibit the growth of cancer cells. Gamma-tocopherols are better than alpha-tocopherols because the former shows apoptosis, inducing cell death mechanisms. In order to prove such theories, many trials have been conducted, and no incidences of decreased cases of cancer cell growth are seen in the patients consuming vitamin E in daily doses of 400 IU or 600 IU.

• Cataracts - Loss of vision is mainly seen in older people. One of the most typical causes includes cataracts. It takes place because of damage caused by free radicals to the proteins. Individuals who take daily vitamin E supplements and have sufficient amounts of the vitamin in the blood show superior lens clarity. According to the age-related eye disease study, over the age of 63, vitamin E does not play a significant role in cataract development.

• Immunity - Vitamin E increases the body's immune response by increasing the phagocytic response and antibody formation process. It also helps in conditions like photodermatitis, dysmenorrhea, etc.

What Happens in the Case of Deficiency?

Vitamin E deficiency is not a common problem as it happens only in patients suffering from a condition where the vitamins do not get absorbed or fat absorption becomes difficult. However, vitamin E deficiency can cause muscle weakness, vision problems, immune system changes, tremors, vertigo, numbness, anemia, etc.

Conclusion

Vitamin E occurs in two main types, tocopherols and tocotrienols, forming stereoisomers as alpha, beta, gamma, and delta forms. It was first used as a supplement by a physician in Canada. After that, many trials were taken to show vitamin E's role in preventing diseases like atherosclerosis, cardiovascular diseases, cancer, cataracts, Alzheimer's disease, etc.