Vitamin A Overdose

Vitamin A Overdose - What are the health risks?

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:

1. Birth defects
2. Liver abnormalities
3. Reduced bone mineral density that may result in osteoporosis

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.

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. The UL was established to help prevent the risk of vitamin A toxicity or overdose. 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.

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

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. 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.

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 carotenoids overdose?

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.

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.

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.

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

Can a vitamin A overdose promote osteoporosis?

Osteoporosis, a disorder characterized by porous, weak bones, is a serious public health problem for more than 10 million Americans, 80% of whom are women.

Another 18 million Americans have decreased bone density, which precedes the development of osteoporosis. Researchers have identified many factors that increase the risk for developing osteoporosis, including being female, thin, inactive, at advanced age, and having a family history of osteoporosis.

An inadequate dietary intake of calcium, cigarette smoking and excessive intake of alcohol also increase the risk of developing osteoporosis. Researchers are now examining a potential new risk factor for osteoporosis: an excess intake of vitamin A.

Animal, human, and laboratory research suggest an association between greater vitamin A intake and weaker bones. Researchers have also noticed that worldwide, the highest incidence of osteoporosis occurs in northern Europe, a population with a high intake of vitamin A. However, decreased biosynthesis of vitamin D associated with lower levels of sun exposure in this population may also contribute to this finding.

One small study of nine healthy individuals in Sweden found that the amount of vitamin A in one serving of liver may impair the ability of vitamin D to promote calcium absorption.

To further test the association between excess dietary intake of vitamin A and increased risk for hip fracture, researchers in Sweden compared bone mineral density and retinol intake in approximately 250 women with a first hip fracture to 875 age-matched controls.

They found that a dietary retinol intake greater than 1,500 mcg/day (more than twice the recommended daily intake for women) was associated with reduced bone mineral density and increased risk of hip fracture as compared to women who consumed less than 500 mcg per day.

This issue was also examined by researchers with the Nurses Health Study, who looked at the association between vitamin A intake and hip fractures in over 72,000 postmenopausal women.

In this study, women who consumed the most vitamin A in foods and supplements (greater than or equal to 3000 mcg per day as retinol equivalents, which is over three times the recommended intake for adult men and women) had a significantly increased risk of experiencing a hip fracture as compared to those consuming the least amount. (less than 1250 mcg per day of retinol equivalents).

The effect was lessened by use of estrogens but still raises questions about the effects of a high intake of vitamin A. In particular this raises questions about the effect of preformed vitamin A or retinol because retinol intake greater than 2000 mcg per day was associated with an increased risk of hip fracture as compared to a retinol intake less than 500 mcg.

A recent longitudinal study in more than 2,000 Swedish men was the first to measure blood levels of retinol to assess the risk of fractures in men.

The investigators found that the risk of fractures was greatest in men with the highest serum retinol levels (greater than 75.62 mcg per d/l).

The risk of fracture was further increased in men with the highest serum retinol levels. Men with retinol in the 99th percentile (greater than 103.12 mcg per d/l) had an overall risk of fracture that exceeded the risk among men with lower levels of serum retinol by a factor of seven.

High vitamin A intake does not necessarily equate to high serum retinol; serum retinol is regulated by factors besides vitamin A intake, including age, gender, hormones and genetics.

Serum beta carotene, however, was not associated with the risk of fracture. The researchers’ findings, which are consistent with the results of studies in animals, as well as in vitro (laboratory studies) and epidemiologic dietary studies, suggest that intakes above the Upper Limit or approximately two times that of the RDA, may pose subtle risks to bone health that require further investigation. V

Vitamin D, which may contribute to osteoporosis, was not measured. Additional clinical studies evaluating vitamin D and calcium as well as retinol for risk of fracture are warranted.

On the other hand, the Centers for Disease Control reviewed data from the Third National Health and Nutrition Examination survey (NHANES III), 1988-94, to determine whether there was any association between bone mineral density and fasting blood levels of retinyl esters, a form of vitamin A.

Blood levels of retinyl esters in 5,800 participants were in the normal range and researchers did not find any significant associations between bone mineral density and blood levels of retinyl esters.

Additional research is needed to clarify the association between high levels of vitamin A intake and osteoporosis.

There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables (many of which are naturally high in beta-carotene), and increased risk of osteoporosis.

Current evidence points to a possible association with vitamin A as retinol only.

If you have specific questions regarding your intake of vitamin A and risk of osteoporosis, it is recommended that you discuss this information with your physician or other trained health care practitioner to determine what’s best for your personal health.

If your interested, here is a website that has great prices on supplements.

Also, check out the vitamins information page for a more in-depth look at vitamins.

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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