Vitamins are the organic substances necessary in the diet of animals for normal growth, maintenance of health, reproduction, and the proper functioning of the body. Our human body is unable to synthesize vitamins (except vitamin D). Hence they are supplied to the human body from external sources that’s why they are also called “Essential Dietary Factors”.
- All animals need vitamins but every vitamin is not required by all of them. For example, human beings and guinea pigs get scurvy when fed diets that do not provide vitamin C, but dogs, cats, rats, and many other species make this vitamin in their bodies and do not need it in their food.
- Vitamins are classified into two types: fat-soluble and water-soluble vitamins.
- Only Vitamin D is a vitamin synthesized by our body.
- Vitamin requirements vary for various age groups and in certain circumstances, there is an additional need for vitamins such as during pregnancy and lactation.
Types of Vitamins –
Vitamins are a group of heterogeneous substances that differ in their chemical nature and function. They are classified on basis of their solubility in water or fats. Hence, there are two types of vitamins one is fat-soluble and another is water-soluble.
- Fat-soluble vitamins
Vitamin A, Vitamin D, Vitamin E, and Vitamin K come under this category.
- Water-soluble vitamins
Vitamin C and Vitamin B (complex) are the vitamins soluble in water. Vitamin B is a complex vitamin, it is a combination of various vitamins like B1, B2, and so on.
Fat-soluble vitamins are generally associated with fatty foods, such as butter, cream, vegetable oils, and fats in meat and fish. These substances generally contain only traces of B vitamins. Some properties of fat-soluble vitamins are-
- None of the fat-soluble vitamins contain nitrogen in their structure.
- They are more stable to heat than the B vitamins and are less likely to be lost during the cooking and processing of foods.
- They are absorbed from the intestines along with fats and lipids in foods.
- They are not excreted through urine and get stored in the body to a considerable extent.
- Excessive consumption of these vitamins can result in toxicity.
A. Properties and functions of Vitamin A
Vitamin A is found in animal products like meat, milk, fish, etc. In animals, the vitamin is found in the highest concentration in the liver, where it is stored and exists generally as free alcohol or its esterified form.
Vitamin A is alcohol (C20H29OH). Its chemical name is “Retinol” because of its specific function in the retina of the eye. Metabolically active forms of the vitamin include the corresponding aldehyde (retinal) and the acid (retinoic acid).
There is one interesting fact that dark green, orange, and yellow fruits & vegetables are known for their vitamin A value but do not contain Retinol rather they are rich in Carotene (Provitamin A), colored compounds from which the body forms retinol.
Vitamin A value of Carotene is much lower than that of retinol because Carotene is less completely absorbed and used.
Functions of Vitamin A
- Vitamin A is beneficial for human eyes and night vision.
- It resists infection related to the throat, chest, and abdomen.
- It stimulates the production and activity of white blood cells.
- It helps in maintaining healthy endothelial cells.
- It helps in body growth.
- It also helps in reproduction.
Sources of Vitamin A
- Major sources of Retinol –
Animal products (eggs, fish, dairy products), fortified foods, and vitamin supplements.
- Major sources of carotene –
Leafy green vegetables (spinach, broccoli, etc.), orange & yellow fruits and vegetables (carrots, pumpkin, summer squash, mango, etc.), tomatoes, and many more.
Diseases due to lack of Vitamin A –
- Night blindness.
- Irregular patches on the white of the eyes.
- Dry skin or hair
Recommend Intake –
Vitamin A value of food is expressed as retinol equivalent (RE).
1 RE= 1 mcg beta-carotene = 12 mcg other provitamin A carotenoids.
- For men 1000 RE
- For Women 800 RE.
- The intake of Vitamin A is less in infants and children.
B. Properties and functions of Vitamin D
Rickets or osteomalacia is a bone disorder it occurs as a result of calcium and phosphorus deficiency. Cod liver oil has been used to cure this disease since the Middle Ages. It was noticed in the 1920s that when certain foods are exposed to ultraviolet light, they develop the ability to protect animals against rickets. This laid the discovery of Vitamin D. Vitamin D isolated in crystalline form was named calciferol. Vitamin D is both a nutrient we eat and a hormone our bodies make.
Vitamin D is a fat-soluble vitamin that helps our body to retain and absorb calcium and phosphorus; elements crucial for building bone.
Vitamin D is supplied to the body in form of food such as – Cholecalciferol (Vitamin D3) & Ergocalciferol (Vitamin D2).
Do you know? That our human body synthesizes a precursor for Vitamin D called 7- Dehydrocholestrol. This precursor is present within the skin. When skin is exposed to UV light, 7-Dehydrocholestrol is transferred to cholecalciferol, which is then used by our body.
The function of Vitamin D
- It helps in the regulation of Calcium and Phosphorus metabolism in the body.
- It helps in the mineralization of the skeleton and teeth.
- It is very useful for type 2 diabetes.
- It is very useful for bone and muscle strength.
- It is also very useful in reducing the growth of cancerous cells.
Sources of Vitamin D
- Regular exposure of skin to sunlight.
- Fortified milk.
- Cod- liver oil.
- Egg/fish products and many more.
Diseases due to lack of Vitamin D
The Recommended Dietary Intake (RDI) means the amount of Vitamin D a person should take daily for the proper functioning of the body.
- For 19 year adults & above them is 600 IU
- Adults older than 70 years should take 800 IU daily.
C. Properties and functions of Vitamin E
Vitamin E is a fat-soluble vitamin with several forms, but alpha-tocopherol is the only one used by the human body. The most important chemical property of Vitamin E is its antioxidant property. However, the most potent antioxidant is not the most potent vitamin. This latter may be related to the absorption of vitamins from the intestines.
What differentiates Vitamin E from other fat-soluble Vitamins?
Vitamin E is absorbed in the same way as the other fat-soluble vitamins. However, it is stored primarily in fatty tissues and not in the liver, unlike fat-soluble vitamins.
The Vitamin E activity of foods may be considerably reduced in processing, storage, and packaging. About 80% or more of the activity is lost when whole wheat is converted to white bread. Dehydrated foods are particularly susceptible to changes resulting in decreased vitamin E activity, because of their propensity to undergo oxidation. The freezing of vegetables is also known to cause some destruction of vitamin E.
Functions of Vitamin E
- Vitamin E serves to protect the formation of peroxides from polyunsaturated fatty acids, thus preventing the oxidation of the unsaturated fat.
- They are essential for normal reproduction.
- They are needed for the stability of Red Blood Cells (RBCs).
- Also, they are beneficial for the proper functioning of the human body.
Sources of Vitamin E
- Sunflower, safflower, and soybean oil.
- Wheat germ oil
- Peanuts and peanut butter
- Beet greens, collard greens, spinach, broccoli
- Pumpkins, Swiss chard, red peppers, and avocados.
Diseases due to lack of Vitamin E
- Peripheral neuropathy happens due to a deficiency of Vitamin E causes damage to peripheral nerves, usually in the hands or feet, causing weakness or pain.
- Lack of Vitamin E may cause sterility.
- Retinopathy may be caused due to lack of vitamin E. It is damage to the retina of the eyes that can impair vision.
- Erythrocyte hemolysis is seen in infants born before vitamin E is transferred to them from their mother before birth.
- Decreased immune function.
According to the original international standards, 1 IU of vitamin E is the activity of 1 mg of alpha-tocopherol acetate.
1 mg alpha-tocopherol = 1.49 IU
The recommended dietary intake values for Vitamin E are as follows –
- For infants, vitamin E is needed in the quantity of 3-4 mg alpha-tocopherol.
- For children and adolescents, 10 mg alpha-tocopherol is needed per day.
- For adult males and females need 7-13 mg of alpha-tocopherol for proper functioning.
D . Properties and functions of Vitamin K
Vitamin K occurs naturally in two forms-
- Vitamin K1 which is known as phylloquinone occurs naturally in plants like collard greens, kale, spinach, etc.
- Vitamin K2 which is known as Menaquinone is formed as a result of bacterial action in the intestinal tract.
One another type of Vitamin K exists, which is of nutritional importance known as Menadione which is a synthetic form of vitamin K used for Vitamin K supplements.
One very important thing about Vitamin K is Antibiotic medicines may destroy vitamin-K-producing bacteria in the gut, which will reduce Vitamin K levels in our body especially if the medicine is taken for more than a few weeks. Also, Vitamin K is fat-soluble so it is best to eat Vitamin K foods with some fat to improve absorption.
Functions of Vitamin K
- It helps in blood clotting and wound healing.
- It helps in the regulation of Blood Ca level.
- It is necessary for healthy bones.
- Newborn babies normally receive a Vitamin K injection to protect them from bleeding in the skull, which could be fatal.
Sources of Vitamin K
- Green leafy vegetables like spinach, kale, etc.
- Fruits like kiwi, avocado, and many more.
- Soybean and canola oil.
- From eggs, meats, cheese, etc.
Deficiency due to Vitamin K
- Delayed coagulation of blood.
As Vitamin K plays a very important role in the synthesis of prothrombin and other proteins involved in the clotting of blood. Without vitamin K our body cannot produce prothrombin. For healthy life the recommended dietary intake of this is –
- For men 138 mcg (19 years old adults or above )
- For women 122 mcg (19 years old adults or above )