Vitamin A and Beta-Carotene What do they do? Vitamin A helps cells reproduce normally—a process called differentiation. Cells that have not properly differentiated are more likely to undergo precancerous changes. Vitamin A, by maintaining healthy cell membranes, helps prevent invasion by disease-causing micro-organisms. Vitamin A also stimulates immunity and is needed for formation of bone, protein, and growth hormone. Beta-carotene, a substance from plants that the body can convert into vitamin A, also acts as an antioxidant and immune system booster. Other members of the antioxidant carotene family include cryptoxanthin, alpha-carotene, zeaxanthin, lutein, and lycopene, but most of them do not convert to significant amounts of vitamin A.
Where are they found? Dark green and orange-yellow vegetables are good sources of beta-carotene. Liver, dairy, and cod liver oil provide vitamin A. Vitamin A can also be found in vegetarian supplements.
In what conditions might vitamin A or beta-carotene be supportive?
• abnormal Pap smear • acne
• cataract
• measles Who is likely to be deficient? Individuals who limit their consumption of liver, dairy foods, and vegetables can develop a vitamin A deficiency. The earliest deficiency sign is poor night vision. Deficiency symptoms can also include dry skin, increased risk of infections, and metaplasia (a precancerous condition).
How much should I take? In males and postmenopausal women, up to 25,000 IU (7,500 mcg) of vitamin A per day is considered safe. In women who could become pregnant, the safest intake level is being re-evaluated; less than 10,000 IU (3,000 mcg) per day is widely accepted as safe.
The most common beta-carotene supplement intake is probably 25,000 IU (15 mg) per day, though some people take as much as 100,000 IU (60 mg) per day.
Are there any side effects or interactions? Women who are or could become pregnant should take less than 10,000 IU (3,000 mcg) per day of vitamin A to avoid the risk of birth defects. For other adults, intake above 25,000 IU (7,500 mcg) per day can—in rare cases—cause headaches, dry skin, hair loss, fatigue, bone problems, and liver damage.1 Beta-carotene, however, does not cause any side effects, aside from excessive intake (more than 100,000 IU, or 60mg per day) sometimes giving the skin a yellow-orange hue.
Individuals taking beta-carotene for long periods of time should also supplement with vitamin E, as beta-carotene may reduce vitamin E levels.2
Taking vitamin A and iron together helps overcome iron deficiency more effectively than iron supplements alone.3
References:
1. Bendich A, Langseth L. Safety of vitamin A. Am J Clin Nutr 1989;49:358-71.
2. Xu MJ, Plezia PM, Alberts DS, et al. Reduction in plasma or skin alpha-tocopherol concentration with long-term oral administration of beta-carotene in humans and mice. J Natl Cancer Inst 1992;84:1559-65.
3. Mejia LA, Chew F. Hematological effect of supplementing anemic children with vitamin A alone and in combination with iron. Am J Clin Nutr 1988;48:595-600.
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It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over-the-counter medication is also available. Consult your physician, nutritionally-oriented health care practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications.The information presented in HealthNotes Online is for informational purposes only.