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Vitamin A

What is the health risk of too much vitamin A?

Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. There are three major adverse effects of hypervitaminosis A:

birth defects,
liver abnormalities,
reduced bone mineral density that may result in osteoporosis (1)
Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time.

Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and muscular uncoordination (1, 7-9, 41, 42).

Although hypervitaminosis A can occur when very large amounts of liver are regularly consumed, most cases of vitamin A toxicity result from an excess intake of vitamin A in supplements.

The Institute of Medicine has established Daily Tolerable Upper Levels (UL) of intake for vitamin A from supplements that apply to healthy populations (1). The UL was established to help prevent the risk of vitamin A toxicity. The risk of adverse health effects increases at intakes greater than the UL. The UL does not apply to malnourished individuals receiving vitamin A either periodically or through fortification programs as a means of preventing deficiency. It also does not apply to individuals being treated with vitamin A by medical doctors for diseases such as retinitis pigmentosa.

Table 3: Tolerable Upper Intake Levels (UL) for preformed vitamin A in micrograms (ug) and International Units (IU)
for infants, children, and adults (1)

Retinoids are compounds that are chemically similar to vitamin A.

Over the past 15 years, synthetic retinoids have been prescribed for acne, psoriasis, and other skin disorders (43). Isotretinoin (Roaccutane® or Accutane®) is considered an effective anti-acne therapy.

At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne (44-46). The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.

What is the health risk of too many carotenoids?
Nutrient toxicity traditionally refers to adverse health effects from a high intake of a particular vitamin or mineral. For example, large amounts of active, or preformed, vitamin A (naturally found in animal foods such as liver but also available in dietary supplements) can cause birth defects.

Provitamin A carotenoids such as beta-carotene are generally considered safe because they are not traditionally associated with specific adverse health effects.

The conversion of provitamin A carotenoids to vitamin A decreases when body stores are full, which naturally limits further increases in storage levels. A high intake of provitamin A carotenoids can turn the skin yellow, but this is not considered dangerous to health.

Recent clinical trials that associated beta-carotene supplements with a greater incidence of lung cancer and death in current smokers raised concern about the effects of beta-carotene supplements on long-term health. However, conflicting studies make it difficult to interpret the health risk.

For example, the Physicians’ Health Study compared the effects of taking 50 mg beta-carotene every other day to a placebo (sugar pill) in over 22,000 male physicians and found no adverse health effects (47). Also, a trial that tested the ability of four different nutrient combinations to inhibit the development of esophageal and gastric cancers in 30,000 men and women in China suggested that after 5 years those participants who took a combination of beta-carotene, selenium and vitamin E had a 13% reduction in cancer deaths (48).

One point to consider is that there may be a relationship between alcohol and beta-carotene because “only those men who consumed more than 11 g per day of alcohol (approximately one drink per day) showed an adverse response to B-carotene supplementation” in the lung cancer trial (1).

The Institute of Medicine did not set a Tolerable Upper Intake Level (UL) for carotene or carotenoids. Instead, they concluded that beta-carotene supplements are not advisable for the general population. As stated earlier, however, they may be appropriate as a provitamin A source or for the prevention of vitamin A deficiency in specific populations (1).

Selected Food Sources of Vitamin A

As the 2000 Dietary Guidelines for Americans state, “Different foods contain different nutrients. No single food can supply all the nutrients in the amounts you need” (49). The following tables list a variety of dietary sources of vitamin A and provitamin A carotenoids.

As the tables show, liver, eggs and whole milk are good animal sources of vitamin A. Many orange fruits and green vegetables are good sources of provitamin A carotenoids. Including these foods in your daily diet will help you meet your daily need for vitamin A.

In addition, food manufacturers fortify a wide range of products with vitamin A. Breakfast cereals, pastries, breads, crackers, cereal grain bars and other foods may be fortified with 10% to 15% of the Daily Value (DV) for vitamin A. If you want more information about building a healthful diet, refer to the Dietary Guidelines for Americans (49) and the Food Guide Pyramid (50).

Table 4: Selected Animal Sources of Vitamin A (18)

Animal sources of vitamin A provide the best aborbed form of this vitamin

Table 5: Selected Plant Sources of Vitamin A (from beta-carotene) (18)

Plant sources of beta-carotene are not as well absorbed as animal sources of vitamin A, especially when they are consumed whole and raw. However, they are still a valuable source of this vitamin.

Vitamin A: What is it?

What foods provide vitamin A?

When can vitamin A deficiency occur?

What is the health risk of too much vitamin A?