A brief overview of vitamin A. Including the daily requirement, functions, toxicity, and sources.
Vitamins have been defined as, organic compounds, occurring in natural foods, which are required in minute amounts, basically for normal nutrition and health. They are important for basic things like, growth, and reproducing offsprings, and besides that normal overall health.
Well, vitamins are different from other organic food such as carbohydrates and proteins, this is because vitamins do not enter inside the tissues and cells of the body, and they are not degraded or converted to other forms for the energy requirements of the body, unlike the carbohydrates.
Now let’s have a look at the details of vitamin A, As, chemically vitamins are classified as fat-soluble, and water-soluble, vitamin A belongs to the fat-soluble group. Vitamin A is found in two different forms naturally, vitamin A one, and vitamin A two. Vitamin A one, is more potent in action as compared to vitamin A two, which has approximately the 40 percent of the biological activity of vitamin A one.
Moving on to the functions of vitamin A, the major proved function of vitamin A is in vision, if we take a closer look in the eyes, in the retina there are rod, and cone cells present. The rod cells detect the light entering the eyes, and they stop sending signals to the brain when light is present, so basically, they get switched off, This stopping of signals tells the brain that light is entering the eyes, and we are able to see during day time, Now, to turn the rod cells back on so that they can signal the brain again, vitamin A is required, And if vitamin A is absent the rods won’t turn on and the brain will take it as day time even at night, and we won’t be able to see at night time, which is called night blindness.
Furthermore, vitamin A has experimentally proved in rats, to be important for reproduction, because in males, without vitamin A, the sperm is not matured, and in the females, vitamin A deficient females, might not be able to reach the full term of pregnancy, thus, it would be difficult to reproduce.
The third function of vitamin A, is maintaining normal epithelial linings of the body, such as the skin, and epithelium of, the cornea, respiratory tract, and urinary tract, Without vitamin A, these epithelial linings become dry, rough, and scaly, all of which are called, keratinization, This can make us prone to many diseases.
Vitamin A also plays an important role in the development of bones, and teeth, And in the case of vitamin A deficiency, the bones lose their fine structural details, and if the deficiency occurs at an early age, bone development, is arrested. The Teeth become unhealthy, due to the thinning of enamel, and chalky deposits on the surface of the teeth are seen,
Vitamin A, along with other vitamins, is principally involved in growth, Its role in cell differentiation, and cell division, has been proved, It may also be involved in protein synthesis inside the body.
Other then all that, vitamin A has been shown to have antioxidant activity, as well as, anticancer activity, in its precursor form as beta carotene.
Well, besides all these benefits, if vitamin A is taken in excess amounts, it can cause toxicity, The vitamin A toxicity, is known as hypervitaminosis A syndrome, which involves, the alteration of skin, and mucus membranes, hepatic dysfunction, plus headache, and the feeling of drowsiness, and it may cause peeling of skin, around the mouth and other parts, In rare situations, if the high levels of vitamin A, remain in the body for a long period, it causes, roughening of skin, irritability, coarsening and falling of hair, anorexia, and loss of weight.
The normal daily requirement, of vitamin A is around 900 micrograms in adult males, and 700 micrograms, in adult females, this daily requirement is normally higher, in growing children, pregnant women, and lactating mothers. Furthermore, to prevent the toxicity, the daily intake of vitamin A, should not exceed 3000 micrograms.
So, where would you get vitamin A from? well, the dietary animal sources are liver oil, butter, milk, cheese, and egg yolk. Whereas the plant sources give vitamin A, in the form of beta carotene, and include, tomatoes, carrots, green-yellow vegetables, spinach, and fruits, such as mangoes, papayas, corn, sweet potatoes, in addition to this, the Spirulina species of algae, have been found to be a good source of vitamin A, here we are done with the overview of vitamin A.
Light Sting by Kevin MacLeod is licensed under a Creative Commons Attribution licence (
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