You may have heard from your grandma that eating carrots can improve you vision. That may not be exactly true, but carrots do contain something called provitamin A carotenoids. These are pigments in some plants that can be converted by the body into vitamin A, and vitamin A is important to your vision, but that's the only thing it's good for.
Vitamin A is also helpful to bone growth and your immune system. As with other vitamins, there are different forms of vitamin A. One of the forms that is most usable to the body is called retinol, which is found in liver, eggs, and milk. One of the most common provitamin A carotenoids that the body converts easily to retinol is beta carotene. Beta carotene is found in yellow and orange fruits and vegetables including carrots, sweet potatoes, spinach, and cantaloupe. Vitamin A is also one of the vitamins often used to fortify breakfast cereals.
Vitamin A is fat soluble, which means that the body stores it, mostly in the liver. That also means that it is possible to build up toxic levels of Vitamin A. This rarely happens from food sources because as the body builds up supplies of vitamin A it will slow down the conversion of beta carotene. When people do get vitamin A toxicity, it is usually from taking too much in supplemental or pill form. Toxic levels of vitamin A can cause liver problems, central nervous system problems, deterioration of bone density, and birth defects.
True deficiency of vitamin A is rare in the US, but common in countries where malnourishment is widespread. As mentioned earlier, vitamin A is important to the immune system and vision. This is because the body uses vitamin A to make various internal tissues, such as those lining the eye, lungs, and intestinal tract. When these linings are weakened by vitamin A deficiency, it is easier for harmful bacteria to penetrate them and thus, people with vitamin A deficiency are more prone to infections, illness, blindness, and respiratory problems.
Aside from the malnourished, other people who may be prone to vitamin A deficiency include those who consume large amounts of alcohol and those with certain metabolic disorders that affect how fat and other nutrients are absorbed by the body.
Some recent and ongoing studies involving vitamin A and beta carotene include investigations as to whether high amounts of vitamin A contribute to osteoporosis, and whether beta carotene can lower the risk of some forms of cancer.
As of this writing the Recommended Daily Intake for Vitamin A was 2,310 IU for females and 3,000 IU for males. For a current list of recommendations and list of foods that contain Vitamin A from the National Institutes for Health visit http://ods.od.nih.gov/factsheets/vitamina/