Vitamin A Nutrition
Vitamin A is a fat soluble vitamin required to maintain healthy skin, teeth, soft tissue, skeleton and mucous membrane. Vitamin A is derived from two sources – provitamin carotenoids and preformed retinols. Carotenoids have the highest vitamin A activity for example beta carotene and are found in dark and yellow/orange vegetables and plants. Retinoids that is retinoic acid and retinal are mainly found in animal sources like organ meats, eggs and dairy products. Caratenoids like beta carotene, alpha carotene and gamma carotene are sometimes referred as 'pro-vitamin A' as the body can convert these into vitamin A.
Vitamin A nutrition is very important as this fat soluble vitamin is required for different physiological functions in the body. Vision is the best known function of vitamin A. Rhodopsin a photopigment in the human retina helps the rod cells to detect small amount of light and adapt eye to night vision and low light condition. The other three photopigments, collectively known as iodopsins found in cone cells of retina plays a fundamental role for the day vision. Besides vitamin A also plays an important role in immune function, cell growth, bone growth, reproduction and breast feeding.
Food sources of vitamin A
Retinol is found in foods that mainly come from animal origin like liver, kidneys, eggs and milk and milk products. Carotenoids are found in dark vegetables and other yellow orange fruits like carrots, spinach, sweet potato, cantaloupes, mangoes, papaya and apricots. Animal sources of vitamin A are well absorbed and utilized by the body than compared to plant sources.
Vitamin A deficiency and toxicity
Vitamin A deficiency is common in developing countries and is often associated with strict dietary restrictions or excess alcohol consumption. An inadequate intake of this fat soluble vitamin or vitamin A deficiency can affect the health of the eyes, hair, skin, and immune system. Bone abnormalities, loss of appetite, and growth retardation are also associated with vitamin A deficiency. A prolonged untreated deficiency of vitamin A can cause night blindness due to impaired production of rhodopsin.
When vitamin A is taken in high amounts then it can cause side effects or toxicity. Toxicity can occur when high doses are ingested (accidently), as high as 660,000 IU by adults and 330,000 IU by children. Although a high dose can not cause an irreversible damage to an adult or child, it can cause severe birth defects and be toxic to the growing fetus. So before starting any supplements for this vitamin it is suggested to consult a specialist for correct recommendation and guidance.