Vitamin A plays an important role in vision, bone growth, reproduction, cell division and cell differentiation, which is the process by which a cell decides what it is going to become. It helps maintain the surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, bacteria can enter the body and cause infection. Vitamin A also helps maintain the integrity of skin and mucous membranes that function as a barrier to bacteria and viruses. Vitamin A helps regulate the immune system. Vitamin A may help lymphocytes, a type of white blood cell that fights infections, function more effectively.

It is important to regularly eat foods that provide vitamin A or beta-carotene even though vitamin A is stored in the liver. Stored vitamin A will help meet needs when intake of provitamin A carotenoids or preformed vitamin A is low.

In the United States, RDAs for vitamin A are listed as Retinol Activity Equivalents (RAE) to account for the different activities of retinol and provitamin A carotenoids. In the table below, RDAs are also listed in International Units (IU) because food and some supplement labels list vitamin A content in International Units (1 RAE in micrograms (ug) = 3.3 IU). The 2001 RDAs for adults and children (21) in ug RAE and IUs are:

300 ug or 1000 IU per day in children aged 1-3,
400 ug or 1333 IU per day in children aged 4-8,
600 ug or 2000 IU per day in children aged 9-13,
900 ug or 3000 IU per day in those 14 and over.

There is no RDA for beta-carotene or other provitamin A carotenoids. The Institute of Medicine report suggests that consuming 3 to 6 mg of beta-carotene daily will maintain plasma beta-carotene blood levels in the range associated with a lower risk of chronic diseases. A diet that provides five or more servings of fruits and vegetables per day and includes some dark green and leafy vegetables and deep yellow or orange fruits should provide recommended amounts of beta-carotene.

Vitamin A deficiency rarely occurs in the United States, but it is still a major public health problem in the developing world.

There is increased interest in subclinical forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause overt deficiency symptoms. This mild degree of vitamin A deficiency may increase children’s risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness.

Low plasma retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories and zinc. These nutrients are needed to make Retinol Binding Protein (RBP), which is essential for mobilizing vitamin A from your liver and transporting vitamin A to your general circulation.

Fat malabsorption can promote diarrhea and prevent normal absorption of vitamin A. This is most often seen with cystic fibrosis, sprue, pancreatic disorders, and after stomach surgery. Healthy adults usually have a reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of temporary or short term fat malabsorption. Long-term problems absorbing fat, however, may result in deficiency, and in these instances physicians may advise vitamin A supplementation.