Vitamin A is the first vitamin to be discovered so that is why it is named after the first letter of the alphabet. Its main functions are to keep the eyes healthy, help in boosting the immune system and aid in cell growth and repair. It can be absorbed in the body by direct absorption process or by conversion of the beta carotene to Vitamin A.
The source of this vitamin is found on foods like eggs, liver, meat and egg. It can also be taken purely like the ones that are sold in the market. The beta carotene is most likely found mostly in fruits and vegetables; especially the orange, red and green ones. However, you must always remember never to consume too much pure Vitamin A because it is oil based. Oil based vitamins are difficult to excrete in our body and so too much consumption may lead to vitamin A toxicity. It will be better to know the recommended dietary allowance for this vitamin according to your gender, age, weight and other factors as well. Since vitamin A may lead to toxicity if taken purely, it is advisable to just take in foods that are rich in beta carotene. There is no known limit on how far we can tolerate beta carotene in our body.
It is true that eating carrots a lot can help you see clearer in the dark. Carrots produce high levels of beta carotene which is then converted into vitamin A. Other food like the tomatoes, spinach and other dark green leafy veggies have higher amount of beta carotene which is actually a good source for vitamin A.
Beta carotene is not only known for vitamin A conversion, but it is also a good antioxidant itself. Since not all consumed beta carotene is converted, the excess amount of helps fight off harmful radicals inside the body. On the other hand, Vitamin A helps fight different illnesses and infections through the first line of our body's defense mechanism. This defense mechanism includes the secretions in the eyes, nose, mouth, throat and even lungs. This vitamin also helps in repairing and growing of the tissues that are damaged due to the infection. The children are also required to take recommended dietary consumption of Vitamin A for proper bone and teeth development.