Vitamin A is the fat-soluble vitamin that is stored in fat tissues in the body. The animal sources have retinol, the preformed vitamin A while the plant sources have pro-vitamin A in the form of carotenoids. Human body converts both plant and animal forms of vitamin A into retinal and retinoic acid.
Vitamin A is needed for night vision and to maintain healthy eyes. Rhodopsin is the photopigment present in rod cells of eyes and is responsible for night vision. Rhodopsin is made of opsin protein and retinal.
Vitamin A is required by the body to stimulate the osteoblasts for bone remodelling. Vitamin A serves to protect the cornea, the outer most layer of eye, and conjunctiva. Vitamin A also maintains the epithelial tissue of skin, lungs, ear and intestine.
Vitamin A maintains the healthy immune system by regulating the growth of T lymphocytes, an important cell type of immune system. Provitamin A (carotenoids) serves as antioxidants and reduces the risk of diabetes, cardiovascular disease and cancer.
Vitamin A is required for normal functioning of the reproduction system as it regulates gamete formation in both males and females.
Night blindness is the deficiency disease caused by prolonged vitamin A deficiency and it is characterized by the inability to see under dim light conditions.
Vitamin A is toxic in higher doses and its deficiency leads to stunted growth. Vitamin A toxicity is characterized by drowsiness, irritability, headache, vomiting, dry and scaly skin, fatigue, joint pain and coma.
Yellow and dark green vegetables such as spinach, carrots, broccoli, and yellow squash are some of the rich plant sources of vitamin A.