VITAMIN A: RETINOL

1. VITAMIN A: RETINOL

Vitamin A, also called retinol, has many functions in the body. In addition to

helping the eyes adjust to light changes, vitamin A plays an important role in bone 

growth, tooth development, reproduction, cell division, gene expression, and regulation 

of the immune system. The skin, eyes, and mucous membranes of the mouth, nose, throat and lungs depend on vitamin A to remain moist. Vitamin A is also an important antioxidant that may play a role in the prevention of certain cancers.

 Food Sources for Vitamin A

Eating a wide variety of foods is the best way to ensure that the body gets enough

vitamin A. 

The retinol, retinal, and retinoic acid forms of vitamin A are supplied primarily by 

foods of animal origin such as dairy products, fish and liver. 

Some foods of plant origin contain the antioxidant, betacarotene, which the body

converts to vitamin A. Beta-carotene, comes from fruits and vegetables, especially those 

that are orange or dark green in color. 

Vitamin A sources also include carrots, pumpkin, winter squash, dark green leafy 

vegetables and apricots, all of which are rich in beta-carotene.

The recommendation for vitamin A intake is expressed as micrograms (mcg) of

retinol activity equivalents (RAE). Retinol activity equivalents account for the fact that 

the body converts only a portion of betacarotene to retinol. One RAE equals 1 mcg of retinol or 12 mcg of beta-carotene. The Recommended Dietary Allowance (RDA)for vitamin A is 900 mcg/ day for adult males and 700 mcg/ day for adult females. Compared to vitamin A, it takes twice the amount of carotene rich foods to meet the body’s vitamin A requirements, so one may need to increase consumption of carotene containing plant foods. Recent studies indicate that vitamin A requirements may be increased due to hyperthyroidism, fever, infection, cold, and exposure to excessive amounts of sunlight. Those that consume excess alcohol or have renal disease should also increase intake of vitamin A.

 Vitamin A Deficiency

Vitamin A deficiency is rare, but the disease that results is known as

xerophthalmia. It most commonly occurs in developing nations usually due to

malnutrition. Since vitamin A is stored in the liver, it may take up to 2 years for signs of deficiency to appear. Night blindness and very dry, rough skin may indicate a lack of 

vitamin A. Other signs of possible vitamin A deficiency include decreased resistance to 

infections, faulty tooth development, and slower bone growth.

 Vitamin A toxicity

The Tolerable Upper Intake Level (UL) for adults is 3,000 mcg RAE. It would be 

difficult to reach this level consuming food alone, but some multivitamin supplements 

contain high doses of vitamin A. If you take a multivitamin, check the label to be sure the majority of vitamin A provided is in the form of betacarotene, which appears to be safe. Symptoms of vitamin A toxicity include dry, itchy skin, headache, nausea, and loss of appetite. Signs of severe overuse over a short period of time include dizziness, blurred vision and slowed growth. Vitamin A toxicity also can cause severe birth defects and may increase the risk for hip fractures.