In this Article

• What are vitamins, and why are they important?
• Calcium
• Vitamin D
• Folic acid
• Vitamin E
• Vitamin A
• Vitamin C
• Vitamin B12
• Vitamin B6
• Thiamin (vitamin B1)
• Niacin
• Riboflavin
• Vitamin K
• Vitamins and Calcium Supplements Glossary
• Vitamins and Calcium Supplements Index

Vitamin A

What is it, and what does it do?

Vitamin A is a fat-soluble vitamin that is broken down into two categories: preformed vitamin A comes from animal foods, and provitamin A carotenoid comes from plant foods.

Vitamin A serves many functions:

• helps regulate the immune system to prevent and fight infections



• helps form and maintain healthy teeth, skin, and tissues



• produces the pigments in the retina of the eye



• promotes good vision

How much do I need to consume?

The Recommended Dietary Allowances (RDA) for vitamin A are listed as International Units (IU) of Retinol Activity Equivalents (RAE). This is done to account for the different actions of both forms of vitamin A.

RDA for vitamin A:

There is insufficient information to establish an RDA for vitamin A for infants. In this case, an Adequate Intake (AI) has been established:

What are sources of vitamin A?

Vitamin A can be found in animal and plant foods. The animal food sources are better absorbed and used by the body than the plant sources. There are also many foods that are fortified and enriched with vitamin A.

The content of vitamin A in animal and plant foods (from beta-carotene):

You can find more sources at http://www.nal.usda.gov/fnic/foodcomp/Data/SR20/nutrlist/sr20a320.pdf.

Do I need to take a vitamin A supplement?

Vitamin A is stored in the liver, so there is a supply that can be used during short-term periods when intake is not adequate to meet your needs. People with medical conditions that interfere with the absorption of vitamin A may need to take a supplement. These conditions include celiac disease, Crohn's disease, inflammatory bowel disease, and pancreatic disorders. Because vitamin A can be toxic at high levels, it's best to discuss supplements with your physician.

What happens if I don't have enough vitamin A?

Early vitamin A deficiency leads to impaired night vision, and advanced vitamin A deficiency can lead to corneal ulcers, xerophthalamia (dry eye), scarring, night blindness or total blindness. In developing countries, vitamin A deficiency is an important cause of blindness among children. Children with vitamin A deficiency are also more likely to develop diarrhea and respiratory infections than children who are not vitamin A deficient. Vitamin A deficiency is rare among healthy adults in the United States.

Vitamin A deficiency can also be a problem for people with Crohn's disease, celiac disease, pancreatic disorders, and people who do not consume animal foods.

Is there such a thing as too much vitamin A?

When excess amounts of vitamin A are being stored in your body, the condition is called hypervitaminosis A. The harmful effects of hypervitaminosis A are birth defects, reduced bone density that may result in osteoporosis, central nervous system disorders, and liver abnormalities.

Acute vitamin A toxicity may result from consuming very large quantities of vitamin A over a short period of time. The symptoms are nausea, vomiting, irritability, drowsiness, altered mental status, anorexia, abdominal pain, blurred vision, muscle pain with weakness, and/or headache. Elderly people and people who drink alcohol heavily are more susceptible to vitamin A toxicity.

The Institute of Medicine states that "beta-carotene supplements are not advisable for the general population," although they also state that this advice "does not pertain to the possible use of supplemental beta-carotene as a provitamin A source for the prevention of vitamin A deficiency in populations with inadequate vitamin A."

The Tolerable Upper Limit (UL) for vitamin A is:

In the ATBC trial, subjects given beta-carotene had a higher incidence of lung cancer than subjects not given beta-carotene. The Institute of Medicine did not set ULs for carotene or carotenoids. However, the recommendation is that beta-carotene supplements are not advisable for the general population.

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