Vitamin A Facts, Detailed Information, and Benefits

Vitamin A is a family of fat-soluble vitamins. Retinol is one of the most active or usable forms and is found in animal foods such as liver and eggs and in some fortified food products. Retinol, frequently called "preformed vitamin A" can be converted to retinal and retinoic acid, which are other active forms of this family.

Some plant foods include darkly colored pigments called "provitamin A carotenoids" can be converted to vitamin A as well. In the U.S., roughly 26% and 34% consumed by men and women is provided by provitamin A carotenoids.

Beta Carotene is a provitamin A carotenoid that is more efficiently converted to retinol than other carotenoids.

For example, alpha carotene and b-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta carotene. Lycopene, lutein, and zeaxanthin are other carotenoids commonly found in food.

They are not sources of vitamin A but may have other health promoting properties. The Institute of Medicine (IOM) encourages consumption of carotenoid rich fruits and vegetables for their health promoting benefits.

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.

Vitamin A 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. It also helps maintain the integrity of skin and mucous membranes that function as a barrier to bacteria and viruses.

It helps regulate the immune system. The immune system helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses and may help lymphocytes, a type of white blood cell that fights infections, function more effectively.

Some carotenoids, in addition to serving as a source, have been shown to function as antioxidants in laboratory tests. However, this role has not been consistently demonstrated in humans.

Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases.

Vitamin A Recommended Dietary
Allowance for Children and Adults

The latest recommendations are given in the Dietary Reference Intakes developed by the Institute of Medicine.

Dietary Reference Intakes (DRI) is the umbrella term for a group of reference values used for planning and assessing diets for healthy people. One of those references values, the Recommended Dietary Allowance (RDA), is the average daily dietary intake level sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in each age and gender group.

RDAs 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).

Vitamin A Recommended Dietary Allowances in micrograms (ug) Retinol Activitiy Equivalents (RAE) and International Units (IUs) for children and adults

Results of two national surveys, the third National Health and Nutrition Examination Survey and the Continuing Survey of Food Intakes by Individuals suggested that dietary intakes of some Americans do not meet recommended levels. These surveys highlight the importance of encouraging all Americans to include dietary sources in their daily diets.

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.

If your worried about meeting the Recommended Dietary Allowances, why not try supplementation. Here is a website that has great prices on vitamin supplements.

Additional Vitamin Information

• Vitamin Supplements
• Vitamin A Facts
• Vitamin A Foods
• Vitamin A Deficiency
• Vitamin A Overdose
• Vitamin B12 Facts
• Vitamin B12 Deficiency

 

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