Vitamin A is an important nutrient for the human body and is composed of a large number of related compounds. The compounds are known as retinol an alcohol and retinal an aldehyde. Retinal is said to be transferred by the human body to retinoic acid, a
vitamin form which affects gene transcription. Retinal, retinol, retinoic acid, and associated compounds are called retinoids. Beta-carotene along with other carotenoids which are converted by the body into retinol are known as
provitamin A carotenoids.
Vitamin A plays a significant role in bone growth, cell division, vision, and cell differentiation.
Vitamin A controls the immune system of the body, which helps in fighting against infections by manufacturing white blood cells that damage harmful bacteria and viruses. Vitamin A also facilitates lymphocytes in fighting infections more effectively.
Vitamin A supports the linings of the eyes and the urinary, respiratory, and intestinal tracts. It becomes easy for bacteria to cause infection by entering the body with the breaking down of those linings.
Vitamin A also facilitates the skin to act as a barrier against bacteria and viruses.
Though some provitamin A carotenoids function as antioxidants, it still needs to be proved in humans. Free radicals are natural by-products of metabolism and can also be formed due to exposure to toxins and pollutants in the environment. Free radicals are potentially dangerous to the human body as it can cause grave damage to the cells resulting in cardio-vascular disease and cancer. These antioxidants protect the cells from free radicals thereby preventing the human body against potentially harmful diseases.
Retinol can be found in foods that are derived from animals like milk, eggs, and liver. In the United States, much of the fat-free milk and dried nonfat milk solids are fortified with vitamin A to replenish the lost amount during the fat removal process. Fortified cereals are also rich in
vitamin A. Provitamin A carotenoids are abundantly found in dark colored fruits and vegetables. The Vitamin A in foods that are derived from animals is absorbed and used sufficiently by the body compared to those which are derived from plants.
Vitamin A is also known as the anti-infective vitamin as it helps in maintaining a healthy immune system. Both excess and deficiency of vitamin A are said to cause birth defects.
Vitamin A also aids in the movement of iron fro storage places to the development of red blood cells to be incorporated within hemoglobin that carries oxygen to the red blood cells.
The main vitamin A deficiency is night blindness resulting in complete blindness with the passage of time. Mild vitamin A deficiency causes changes in the conjunctiva known as Bitot's spots. Severe
vitamin A deficiency causes xeropthalmia (dry eye), a condition distinguished by changes in the cells of the cornea that result in corneal ulcers, scarring, and blindness. Vitamin A deficiency also damages the immune system of our body and been mild deficiency can result in respiratory deficiencies especially among children.
