≈ 700–900 µg/day (recommended amount). Better obtained from the diet, including beta-carotene from fruits and vegetables.
Where there is deficiency, it prevents blindness and reduces child mortality.
In smokers, supplemental beta-carotene INCREASED lung cancer.
See the study (RCT (CARET)) →⏱ 3 min read
Vitamin A is a group of fat-soluble compounds that includes retinol and its esters (the active form of animal origin) and the provitamin carotenoids (especially beta-carotene, alpha-carotene, and beta-cryptoxanthin) present in colorful fruits and vegetables, which the body converts into retinol with variable and limited efficiency; its biological function centers on three critical domains: vision (an essential component of retinal rhodopsin), epithelial cell differentiation (maintenance of mucous membranes, skin, and glandular linings), and cellular immunity (modulation of T lymphocytes and the antiviral response).
Vitamin A deficiency is one of the nutritional deficiencies with the greatest impact on global public health: the WHO estimates that it affects hundreds of millions of children in low-income countries, where it is a major cause of preventable childhood blindness and significantly increases mortality from respiratory and diarrheal infections; in developed countries clinical deficiency is rare, but subclinical deficiencies in specific groups (strict vegetarians without dietary guidance, intestinal malabsorption, alcoholism) have recognized clinical relevance.
The most classic function of vitamin A is vision: retinol is essential for the regeneration of rhodopsin, the photosensitive pigment of the retinal rods responsible for vision in low-light conditions; moderate deficiency causes hemeralopia (night blindness) and, in advanced stages, xerophthalmia (corneal dryness, keratomalacia, and irreversible corneal ulceration that can lead to permanent blindness).
In countries with endemic deficiency, periodic mega-dose supplementation programs (200,000 IU every 4-6 months in children aged 6 months to 5 years) have shown significant reductions in child mortality and preventable blindness, one of the most cost-effective nutritional public health interventions available.
In measles and other viral infections in children with nutritional deficiency, supplementation with two high doses of vitamin A (200,000 IU on days 1 and 2) significantly reduces mortality and serious complications, an intervention recommended by the WHO and validated by multiple clinical trials; the mechanism is multifactorial, including improvement of the respiratory epithelial barrier, modulation of T lymphocytes, and reduction of viral replication.
Pharmacological retinoids derived from vitamin A (oral isotretinoin, topical tretinoin, adapalene) are reference treatments in severe acne, keratosis, and some skin cancers, a well-established dermatological indication; oral vitamin A at supra-pharmacological doses has been used with inconsistent results and with a significant toxicity profile, which is why synthetic retinoids have practically displaced this use.
Unlike most water-soluble vitamins, vitamin A accumulates in the liver and fatty tissue and has a well-characterized chronic toxicity: sustained doses above 10,000 IU per day can produce hypervitaminosis A with headache, nausea, hair loss, skin peeling, hepatotoxicity, hypercalcemia, bone pain and, in children, benign intracranial hypertension; the tolerable upper limit in adults is 10,000 IU per day (3,000 micrograms of retinol).
In pregnancy, vitamin A is teratogenic at high doses: doses above 10,000 IU per day are associated with craniofacial malformations and malformations of the fetal central nervous system, a well-documented toxicity that justifies the prohibition of pharmacological retinoids during gestation and caution with vitamin supplements not specific to pregnancy.
Usual nutritional doses are 700-900 micrograms of retinol equivalents per day in adults (2,300-3,000 IU), provided by a varied diet that includes some animal product (eggs, dairy, occasional liver) or generous amounts of colorful vegetables (carrot, pumpkin, spinach, sweet potato); in people with limited animal intake, carotenoids are a valid source although their conversion to retinol is modest (12:1 factor for beta-carotene).
The most important precautions are limiting the dose to avoid chronic toxicity and avoiding high doses in pregnancy; people with chronic liver disease should avoid supplementation because the damaged liver stores vitamin A abnormally and is further damaged; cod liver oil products are a concentrated source and should be dosed carefully; in multivitamins, beta-carotene is preferable to retinol because its conversion is regulated and it does not cause toxicity through accumulation; smokers should avoid beta-carotene supplements at high doses (more than 20 mg/day) because of the increased risk of lung cancer documented in the CARET and ATBC trials.
Information, not medical advice. Scientific evidence reflects the quality of the studies.