Vitamin A Promotes vision and healthy skin Sources: Liver, eggs, milk, butter, cheese, yogurt, carrots and other yellow vegetables and green leafy vegetables. Read more »

Vitamins are substances needed in small quantities but they are indispensable. They perform specific vital functions and are essential components in any diet. Read more »

There is a paucity of Indian data on the vitamin E content of foods as well as vitamin E requirement by Indian population. Vitamin E deficiency is not prevalent in our country and ICMR has not yet established a daily allowance of vitamin E for our Indian population. Since the requirement for vitamin E depends on the intake of unsaturated essential fatty acids (linoleic and linolenic acids), the requirement for vitamin E suggested is 0.8mg/ g of essential fatty acids.

A person consuming a large amount of PUFA needs more vitamin E. Fortunately, vitamin E and PUFA tend to occur together in the same foods.

The Food and Nutrition Board in the United States has recommended levels of vitamin E intake for various age groups. They have been given in the below table.

Vitamin E is a fat-soluble antioxidant and one of body’s prime defenders against oxidation. It protects the lipids and other vulnerable components of the body cells and their membranes from oxidation.

Its function as an antioxidant is particularly important in tissues rich in polyunsaturated fatty acids (PUFA) and tissues which are in constant contact with oxygen, like lungs. Vitamin E is particularly effective in preventing the oxidation of PUFA, other lipids, as well as related compounds such as vitamin A. Thus, vitamin E protects the lipids of the membranes from oxidative damage due to highly reactive oxygen species and other free radicals. Vitamin E reduces the harmful free radicals to harmless metabolites. This process is called ‘free radical scavenging’.

Vitamin E protects the unsaturated lipids and vitamin A because it can accept oxygen and get oxidised itself, thereby acting as an antioxidant. It thus exerts a sparing action on vitamin A by preventing its oxidation. Vitamin E also protects fats and oils from oxidation and rancidity, thereby acting as a preservative.

Recent researches have shown that vitamin E may play a role in reducing the risk of heart disease by protecting LDL (low density lipoprotein) cholesterol against oxidation. Vitamin E exerts an especially important antioxidant effect in the lungs, where the exposure of the cells to oxygen is maximal. Vitamin E’s antioxidant property protects not only the lung tissues but also the red blood cells and white blood cells that pass through the lungs. Vitamin E also protects the lungs against air pollutants. In its antioxidant function, vitamin E acts synergistically with selenium (a trace element) to protect the cells from the damaging effects of oxygen species and free radicals. In fact, selenium and vitamin E both have a sparing effect on each other, and also reduce the body’s requirement for each other.

antioxidant function of vitamin E and other nutrients protects our body against conditions related to oxidative stress, such as aging, air pollution, arthritis, cancer, cardiovascular diseases, diabetes and infections. A lot of research is being conducted on the role of vitamin E in the above mentioned areas.

False hopes

When vitamin E was discovered in 1922, it was termed as the ‘antisterility factor’ because of its role in fertility and preventing abortions in rats. However, any of these functions have not yet been proven in humans. It is, therefore, a misnomer to call vitamin E the ‘reproduction vitamin’. Till date, it has not been proven that vitamin E can improve sexual potency, prevent baldness, improve athletic performance or increase life-span in humans. Nonetheless, vitamin E’s role as an antioxidant in protecting the membranes in our bodies from damage, is extremely important.

In 1922, Evans and Bishop discovered another fat-soluble factor and named it vitamin E. This factor was found to be essential for reproduction in rats. Although the same functions have not been proven in humans, the vitamin was named tocopherol (vitamin E) from the Greek tokos meaning ‘childbirth’, pherein meaning ‘to bear’ and ol signifying an alcohol.

Vitamin E comprises a group of compounds known as tocopherols and tocotrienols. These are of different types – alpha, beta, gamma and delta. Of these, alpha-tocopherol is the most active and is also the form which is most abundant in foods.

Being fat-soluble in nature, vitamin E and other fat-soluble vitamins are absorbed along with fat in the presence of bile acids. Small amounts of vitamin E are present in all body tissues, but the bulk is stored in muscle, liver, and adipose tissue.

recognised that vitamin E plays a fundamental role in the normal metabolism of all cells. Its deficiency can affect several organ systems. Its functions are related to several other nutrients. Together with some other nutrients, it plays an important role in the defence mechanisms of the body.

Vitamin E is stable to high temperature and acids but it gets oxidised easily in the presence of oxygen. Thus, it acts as an antioxidant. Vitamin E is soluble in fats and organic solvents but insoluble in water. Normal cooking temperatures are not destructive but freezing, processing and frying result in vitamin E losses.

Only a few foods contain vitamin D naturally. Fortunately, the body can make all the vitamin D within itself with the help of a little sunshine.

Vitamin D in foods

Most foods have negligible amounts of vitamin D. Most of the plant foods are poor sources of vitamin D. Some foods of animal origin like egg yolk, liver, fatty fish, butter and fortified milk, provide variable amounts of the vitamin. Vitamin D content of selected foods is given in below table

Vitamin D from the sun

Most of the world’s population relies on natural exposure to sunlight to maintain adequate vitamin D nutrition. The sun imposes no risk to vitamin D toxicity. For most people, exposing hands, face, and arms on a clear summer day for 10 to 15 minutes, at least 3 times a week, should be sufficient to maintain vitamin D nutrition.

Dark-skinned people require longer sunlight exposure than others, to derive the same amount of vitamin D from sunlight exposure. The ultraviolet rays of the sun, which promote vitamin D synthesis, can be blocked by heavy clouds, smoke, or fog. People who are unable to go outdoors frequently or dark-skinned people who live in cloudy or smoggy cities should consume foods fortified with vitamin D or therapeutic supplements to prevent its deficiency.

Vitamin D plays an essential role in the metabolism of calcium and phosphorus. Calcium is required for the development of bones and teeth. Blood calcium levels have to be very tightly maintained for normal functioning of the nervous system. The prohormone vitamin D, which gives rise to the hormone calcitriol, regulates blood calcium levels within a narrow range.

Vitamin D in bone growth

Vitamin D plays a special role in bone growth by making calcium and phosphorus available in the blood. When the blood calcium level becomes too low – for example, when calcium intake from diet is inadequate – the parathyroidgland secretes parathyroid hormone(PTH).

PTH promotes the activation of vitamin D to calcitriol, the active form of the vitamin. Calcitriol restores normal blood calcium in three ways – by facilitating absorption of dietary calcium from the intestine, increasing the mobilisation of calcium from the bone into the blood, and increasing the
reabsorption and retention of calcium by the kidneys. These actions increase the levels of calcium and phosphorus in the blood. Normal calcium
levels permit deposition of calcium in bones and teeth. It is also important for normal nervous function and muscle contraction.

Vitamin D in other roles

Scientists have discovered other roles for vitamin D. Vitamin D has been found in many other tissues such as the brain, nervous system, pancreas,
skin, muscles, reproductive organs, liver, kidneys, hormone secreting glands, etc. Vitamin D may have some important role in these tissues as well.

Daily allowances of vitamin D ICMR has not established a daily allowance of
vitamin D for our Indian population, because plenty of sunlight is already available in a tropical country like ours. It is not known how much of
vitamin D is exactly required by our body through diet and sunlight. The vitamin D requirementof children is placed between 200-400 International Units (100 IU = 2.5mg). The requirement is lesser for older age groups. The
allowance for older age groups is difficult to establish because of exposure to sunlight. Vitamin D requirements have been suggested for different
age groups in below table.

The requirement for vitamin D can be obtained in great measure through exposure to adequate sunlight. Only in cases where vitamin D requirement is not met through adequate exposure to sunlight or due to metabolic or genetic reasons, therapeutic supplementation of vitamin D may be necessary.

Vitamin D was first recognised by McCollum as the component of ‘good fats’ that cured rickets. Chemically, compounds with vitamin D activity are sterols. The two forms of the vitamin, which are important, are vitamin D2 (ergocalciferol) of plant origin and vitamin D3 (cholecalciferol) of animal origin. Vitamin D2 is formed when ergosterol (found in plants) is exposed to ultraviolet rays. Vitamin D3 is the chief form occurring in animal cells and develops in the skin on exposure of 7-dehydrocholesterol to ultraviolet rays from sunshine.

Dietary vitamin D is absorbed along with food fats from the intestine; bile salts are essential for effective absorption. Disease conditions in which fat absorption is affected also hinder vitamin D absorption. Vitamin D made in the skin enters the blood where it circulates attached to a specific protein.

Vitamin D itself is an inactive, storage form of the vitamin concentrated in the liver. It is rapidly hydroxylated (addition of-OH group) to 25-hydroxy vitamin D3 (calcidiol) in the liver. Calcidiol is further hydroxylated to 1, 25-dihydroxy vitamin D3 (calcitriol) in the kidney. Calcitriol is considered the active form of the vitamin, which acts as a hormone in calcium metabolism. As vitamin D is necessary for proper bone calcification, it is also called calciferol (to signify an alcohol promoting calcification). Vitamin D is soluble in fats and organic solvents but insoluble in water. It is stable to heat and is not easily oxidised.