Vitamin A is a fat-soluble vitamin necessary for maintaining vision,
epithelial (mucous) membranes, bone growth, and immunity. Most commonly known
for its importance in preventing "night-blindness," vitamin A is an important
part of the visual pigment molecules present in all retinal cells (both rods and
cones) and plays a vital role in both day and night vision. Vitamin A has long
been known as the "anti-infective" vitamin and plays an important role in the
proper functioning of the immune system. Vitamin A maintains the integrity of
all mucous membranes, which is the body's first line of defense against
infection. When the body is deficient in vitamin A, mucus-producing cells are
replaced by keratin-producing cells. The secretion of mucus diminishes and the
mucous membranes become tough and relatively inflexible, leaving the body
defenseless against invading organisms. Vitamin A stimulates white blood cell
function and increases antibody response.
Vitamin A is required during the growth of cell membranes and also for repair
of cell membranes during wound healing. Other functions of vitamin A include
glycogen synthesis, protein metabolism, hormone synthesis, and as a coenzyme in
the skin, bone, retina, liver, and adrenal glands.
Vitamin A is only found in foods of animal origin. Beef, calf, and chicken
liver are the richest sources. Vitamin A is also found naturally in whole milk
and butter. Lowfat and skim milk is fortified to replace the vitamin A that is
lost when the fat is removed from the milk. Dairy products supply about half of
the vitamin A consumed by most individuals. The other half is supplied by fruits
and vegetables that are rich in beta-carotene, the vitamin A precursor that is
readily converted to vitamin A in the body. Beta-carotene is abundant in orange
and dark green leafy vegetables and fruits. Refer to the section on
beta-carotene for a full listing of good food sources.
There are three different forms of vitamin A: retinol, retinal, and retinoic
acid. Retinal and retinoic acid appear to be the active forms of retinol.
Retinal is primarily involved with vision and reproduction, while retinoic acid
is important for growth and cell differentiation.
Natural vitamin A is available as retinol or retinyl palmitate. All forms are
easily absorbed. Supplemental vitamin A is available in tablets or capsules of
10,000 IU, 25,000 IU, or 50,000 IU.
- Treatment of skin disorders, primarily acne and psoriasis
- Immune system enhancement, especially against viral
- Reduces infant mortality from measles
- Treatment of severe burns and other wounds
- Night blindness;
|Dosage Ranges and Duration of
As of 1980, vitamin A is measured as retinol equivalents or RE. One RE
corresponds to the biological activity of 1 mcg of retinol. However,
supplemental vitamin A is still most commonly expressed in international units
or IU. One RE is equal to 3.33 IU of retinol.
The current RDAs expressed in RE are 1,000 mcg RE for men, and 800 mcg RE for
women. However, for convenience in determining supplement dosages, the following
RDA information is expressed in both RE and IU.
- Infants up to 1 year:1,875 IU400 mcg RE
- 1 to 3 years:2,000 IU400 mcg RE
- 4 to 6 years:2,500 IU500 mcg RE
- 7 to 10 years:3,500 IU700 mcg RE
- Males over 10 years: 5,000 IU1,000 mcg RE
- Females over 10 years:4,000 IU800 mcg RE
- Pregnant women:5,000 IU1,000 mcg RE
- Lactating women:6,500 IU1,200 mcg RE
To reverse vitamin A deficiency or to prevent deficiency during acute viral
infection, a single oral dose of 50,000 IU for one or two days is safe even for
infants. Adults and children over 8 years can tolerate up to 50,000 IU daily for
up to two weeks. In general, daily doses of up to five times the RDA (25,000 IU
for adults and 12,000 IU for children) have been found to be safe. However, a
health care provider must continue to monitor any high dose therapy. This
applies especially to treatments for skin disorders. For other health issues,
beta-carotene is the preferred supplement, as it may be administered in
significantly higher doses without the same risk of toxicity. Pregnant women
must avoid any type of vitamin A supplements (beyond what is found in prenatal
vitamins), due to the higher risk of birth defects.
Vitamin A toxicity (hypervitaminosis A) has been widely studied. Tolerance
varies among individuals and may be related to liver function status as well as
other variables such as body weight. Doses of 1 million IUs taken daily for five
years have been tolerated by some people, while others show symptoms of toxicity
with doses as low as 25,000 IU per day. Children are most susceptible to vitamin
A toxicity, especially if they take multiple vitamins along with fortified
foods. Vitamin A toxicity in the fetus can occur if pregnant women take more
than 6,000 IU per day.
Overdoses or chronic excesses affect the same body systems that are affected
by vitamin A deficiency, and some of the symptoms of toxicity and deficiency are
the same. The most common symptom of toxicity is increased intracranial pressure
exhibited as chronic headache. Other symptoms of vitamin A toxicity and
deficiency are as follows: abdominal pain, muscle and joint pain, fatigue, dry,
cracking skin and lips, dry eyes, conjunctivitis, alopecia, anorexia, nausea,
diarrhea, leukocytosis, and bone fractures.
Supplementation with vitamin A over 6,000 IU/day is associated with birth
defects, and pregnant women should avoid any vitamin A treatments or supplements
beyond what is contained in prenatal vitamins.
Patients must be closely monitored by their provider for any symptoms of
toxicity during high dose therapy for skin conditions using isotretinoin
Most multivitamins contain the RDA of 5,000 IU of vitamin A. Dairy products
and fortified foods contribute an additional 2,500 IU/day or more. Patients
should be careful of using additional fish liver oil supplements or products
formulated for "eye health," "immune system enhancement," "skin formulas,"
"acne formulas," or "bone or joint repair." Any of these formulas are likely to
contain additional vitamin A. Always check the labels for vitamin A content, and
be careful that daily intake does not exceed the recommended safety levels.
Vitamin A is contraindicated for use in individuals with chronic kidney or
Overuse of alcohol makes vitamin A toxicity more likely to
A multi-center, randomized, prospective study involving 60 patients with
chronic gastric ulcers evaluated the effects of vitamin A supplementation on
ulcer healing (Patty et al. 1983). Patients were divided into three groups and
treated for four weeks with antacids only, antacids plus vitamin A (50,000 IU po
tid), or antacids, vitamin A, and cyproheptadine (4 mg po tid). Endoscopic
analysis revealed that gastric ulcers were completely healed in 15 out of 40
patients who received vitamin A. The reduction in ulcer size was greater in the
group receiving vitamin A plus antacids after both two and four weeks of use.
This study suggests that the combination of vitamin A and antacids may be more
effective than antacids alone to heal
HMG-CoA reductase inhibitors may increase blood vitamin A levels (Muggeo et
In one study involving 17 patients with severe cystic acne, subjects received
isotretinoin (0.5mg/kg/day) for 3 months; eight patients continued to receive
isotretinoin (0.75 mg/kg/day) for another 3 months (Rollman and Vahlquist 1986).
After 3 months of therapy, epidermal retinol content increased by 53%, while
dehydroretinol decreased by 79%. These findings were corroborated in another
study with 22 subjects (Vahlquist et al. 1990). Administration of isotretinoin
(1 mg/kg/day) for four months led to a marked increase in retinol and a decrease
in dehydroretinol content in the skin. Individuals should avoid consuming high
doses of vitamin A while taking tretinoin unless prescribed by a physician.
In a double-blind study in five healthy males, study participants consumed a
standard meal containing vitamin A (300,000 IU) followed by either neomycin
sulfate (2 g) or placebo (Barrowman et al. 1972). The rise in plasma vitamin A
levels was significantly less after neomycin treatment in all study subjects.
Neomycin interferes with the absorption of vitamin A when delivered in a very
large bolus dose. The significance of this interaction on daily supplementation
of vitamin A is
Omeprazole significantly suppressed the blood response to beta-carotene (120
mg po) in healthy subjects (Tang et al. 1996). Serum beta-carotene levels were
significantly greater during the low gastric pH phase of the study compared to
the high gastric pH phase. It is not known if omeprazole or lansoprazole
adversely affect carotenoid absorption from
Oral contraceptives increase the levels of vitamin A in women (Tyrer 1984).
Barrowman J, Broomhall J, Cannon A, et al. Impairment of vitamin A absorption
by neomycin. Clin Sci. 1972;42:17P.
Eades MD. The Doctor's Complete Guide to Vitamins and Minerals. New
York, NY: Dell Publishing; 1994:48.
Fawzi WW. Vitamin A supplementation and child mortality. JAMA.
Fawzi WW, Mbise RL, Hertzmark E, et al. A randomized trial of vitamin A
supplements in relation to mortality among human immunodeficiency virus-infected
and uninfected children in Tanzania. Pediatr Infect Dis J.
Fortes C, Forastiere F, Agabiti N, et al. The effect of zinc and vitamin A
supplementation on immune response in an older population. J Am Geriatr
Futoryan T, Gilchrest BA. Retinoids and the skin. Nutr Rev.
Kindmark A, Rollman O, Mallmin H, et al. Oral isotretinoin therapy in severe
acne induces transient suppression of biochemical markers of bone turnover and
calcium homeostasis. Acta Derma Venereol. 1998;78:266-269.
Melhus H, Michaelsson K, Kindmark A, et al. Excessive dietary intake of
vitamin A is associated with reduced bone mineral density and increased risk for
hip fracture. Ann Intern Med. 1998;129:770-778.
Muggeo M, Zenti MG, Travia D, et al. 1995. Serum retinol levels throughout 2
years of cholesterol-lowering therapy. Metab. 1995;44(3):398-403.
Murray M. Encyclopedia of Nutritional Supplements. Rocklin, Calif:
Prima Publishing; 1996.
Nursing '93 Drug Handbook. Springhouse, Pa: Springhouse Corporation;
Patty I, Benedek S, Deak G, et al. Cytoprotective effect of vitamin A and its
clinical importance in the treatment of patients with chronic gastric ulcer.
Int J Tissue React. 1983;5:301-307.
Rollman O, Vahlquist A. Oral isotretinoin (13-cis-retinoic acid) therapy in
severe acne: drug and vitamin A concentrations in serum and skin. J Invest
Semba RD. Vitamin A, immunity and infection. Clin Infect Dis.
Tang G, Serfaty-Lacrosniere C, Camilo ME, Russell RM. Gastric acidity
influences the blood response to a beta-carotene dose in humans. Am J Clin
Tyrer LB. Nutrition and the pill. J Reprod Med. 1984;29(7
Vahlquist A, Rollmann O, Hollan D, Cunliffe, W. Isotretinoin treatment of
severe acne affects the endogenous concentration of vitamin A in sebaceous
glands. J Invest Dermatol. 1990;94:496-498.
Whitney E, Cataldo C, Rolfes S. Understanding Normal and Clinical
Nutrition. St. Paul, Minn: West Publishing Company;
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