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Vitamin A is a fat-soluble micronutrient essential for healthy vision, reproduction, immunity, wound healing, and other crucial bodily functions. In its preformed state vitamin A is derived only from animal sources; it’s also produced synthetically. The most common supplemental forms are retinol and retinyl palmitate. The body is able to convert, however, certain plant-derived carotenoids, particularly beta carotene, to vitamin A.

Why is it essential? 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 microorganisms. Vitamin A is needed for formation of bone, protein, and growth hormone. Vitamin A’s ability to boost the immune system is well established by scientific studies. Vitamin A also supports the functioning of the eyes and ears.

Benefits and uses: Vitamin A improves resistance to infection and may play a role in the prevention or treatment of respiratory infections, recurrent ear infections, urinary tract infection, and vaginitis. It has also shown considerable promise in treating viral illnesses such as measles and AIDS. Dermatologists use vitamin A derivatives to renew aged skin and treat acne. Vitamin A may help treat or prevent eye- and vision-related conditions such as cataracts, night blindness, conjunctivitis and blepharitis, retinopathy, and macular degeneration. It may also help to prevent or treat such conditions as Crohn’s disease, diarrhea, heavy menstruation, peptic ulcer, and premenstrual syndrome.

Daily requirement: The Daily Value for vitamin A is 5,000 IUs for adults.

Deficiency risk factors: The body needs sufficient zinc, vitamin E, and protein to absorb and use vitamin A. An early sign of a vitamin A deficiency is poor night vision. Other potential symptoms are dry skin, increased infections, fatigue, and loss of appetite. Alcoholics, people with liver disease, and the elderly often suffer from vitamin A deficiencies. Taking vitamin A and iron together helps overcome iron deficiency more effectively than iron supplements alone.

Optimal intake: An optimal daily dose for an average adult is 5,000 to 10,000 IU of preformed vitamin A. This can be supplemented with an additional 25,000 to 50,000 IU (15 to 30 mg) of beta carotene or, preferably, beta carotene plus mixed carotenoids.

Food sources: Oils derived from the liver of cod and other fish are the richest sources of vitamin A. Eggs and dairy products also have appreciable levels. Many plants, especially dark green leafy vegetables and orange/yellow vegetables and fruits such as carrots and cantaloupes, provide high levels of beta carotene and other vitamin A precursors.

Recent findings: In two population studies, researchers in Pakistan who studied Indian expatriates living in the Middle East found lower retinol levels in women than men (they also found that the normal average in infants was below what had been considered deficiency levels)¹, and researchers in Iowa found that approximately one in three children from socioeconomically disadvantaged families living in Midwestern states had inadequate vitamin A levels.² Scientists have also recently shown that vitamin A supplementation can reduce the incidence of night blindness during pregnancy. Beta carotene supplements had less of an effect.³

Safety: In males and postmenopausal women, up to 25,000 IU of preformed vitamin A per day is considered safe. Some people may experience symptoms such as headache, dry skin, or fatigue from 25,000 to 100,000 IU per day. Taking more than 100,000 IU of preformed A per day for extended periods of time can allow it to accumulate in the liver and other parts of the body and cause potentially serious adverse health effects, including bone problems, anorexia, and liver damage. In women who could become pregnant, the safest intake level is being re-evaluated; less than 10,000 IU per day is probably safe, though some nutritionists recommend not exceeding the DV of 5,000 IU to avoid the risk of birth defects. Plant-derived vitamin A precursors are virtually nontoxic.

Types of products: Most vitamin A supplements are capsules or softgels in the 10,000 to 25,000 IU range. Vitamin A is often combined with 400 to 1,000 IU of another fat-soluble nutrient, vitamin D. Some vitamin A supplements also include beta carotene or other mixed carotenoids.

References

1. Lindblad, B.S., et al., "Age and sex are important factors in determining normal retinol levels," J Trop Pediatr (1998), 44(2):96–99
2. Spannaus-Martin, D.J., et al., "Vitamin A and vitamin E statuses of preschool children of socioeconomically disadvantaged families living in the midwestern United States," Eur J Clin Nutr (1997), 51(12):864–69
3. Christian, P., et al., "Vitamin A or beta-carotene supplementation reduces but does not eliminate maternal night blindness in Nepal," J Nutr (1998), 128(9):1458–63