How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Vitamin A
Vitamin A reduces mortality in deficient children in 47 trials. In adults, studies mainly highlight its risks at high doses: malformations during pregnancy, fractures, lung cancer in smokers.
Benefits
- Deficient children: in 47 trials conducted mainly in Asia, Africa, and Latin America in children aged 6 months to 5 years, 12 % fewer deaths from all causes, and 12 % fewer deaths from diarrhea.
- In these same children: 15 % less diarrhea, 55 % fewer cases of measles, 58 % fewer Bitot's spots on the eye, and 68 % less night blindness.
- Anemia: a meta-analysis found a 26 % lower risk of anemia and higher hemoglobin levels, especially in people with low blood retinol; ferritin increases in pregnant or breastfeeding women.
- Retinitis pigmentosa: in 601 patients followed for 4 to 6 years, 15,000 IU per day slowed the decline in retinal function.
Precautions
Malformations: in over 22,000 pregnant women, more than 15,000 IU per day of preformed vitamin A (diet and supplements) multiplied the risk of malformations by 3.5; more than 10,000 IU per day from supplements alone, by 4.8. This is the risk on which EFSA bases its limit. Fractures: in over 72,000 postmenopausal women followed for 18 years, an intake of 3,000 µg per day or more was associated with 1.48 times more hip fractures, mainly due to retinol; in Sweden, more than 1.5 mg per day doubled this risk compared to less than 0.5 mg. In 2,322 men followed for 30 years, the highest blood retinol levels were associated with more fractures; a review links osteoporosis to intakes barely twice as high as the recommendations. Lung cancer: in over 18,000 smokers, former smokers, or workers exposed to asbestos, 30 mg of beta-carotene and 25,000 IU of vitamin A per day increased the risk of lung cancer by 28 %, as well as deaths; the trial was stopped early. Mortality: in a meta-analysis of 68 trials and over 232,000 participants, beta-carotene, vitamin A, and vitamin E, alone or combined, increased mortality in the most reliable trials. Immunity: in elderly people, 800 µg of retinol per day reduced certain lymphocytes (T CD3+ and CD4+), whereas zinc improved the immune response. Inflammation: a meta-analysis in adults found C-reactive protein (an inflammatory marker) to be higher with vitamin A. Children: the given dose multiplied the risk of vomiting within 48 hours by 1.97. Limits: adult women: in over 200,000 women in Ghana, 25,000 IU per week reduced neither pregnancy-related mortality nor overall mortality. Children: no effect on deaths from measles or respiratory disease, nor on respiratory infections and hospitalizations for diarrhea or pneumonia. Bones: conflicting results: in over 34,000 women from Iowa, little evidence of an increased risk (1.18 times more hip fractures in supplement users, with no dose-response relationship); nearly 1,000 adults on 7.5 mg per day long-term did not have more fractures; 6 weeks at 7,576 µg per day did not alter bone remodeling in 80 men. Iron: no decrease in iron deficiency in children and adolescents. Studies on fractures and pregnancy observe individuals without assigning them a treatment: they show an association, not proof that vitamin A is the cause.
Recommended dosage
EFSA limit: 3,000 µg per day of preformed vitamin A. Trials: from 800 µg to 7.5 mg of retinol per day (15,000 to 25,000 IU).
How to take it
- Who it is for: the measured benefits concern deficient children from Asia, Africa, and Latin America, and patients with retinitis pigmentosa; no trial in this fact sheet shows a benefit in healthy adults.
- Do not exceed: EFSA sets the upper limit for preformed vitamin A in adults at 3,000 µg per day, based on the risk of malformations.
- Pregnancy: above approximately 10,000 IU per day from supplements, the risk of malformations is multiplied by 4.8; supplementation is decided on a case-by-case basis.
- If you smoke: EFSA recommends avoiding beta-carotene as a supplement, and the CARET trial (beta-carotene and vitamin A combined) increased lung cancers.
- Form: trials mainly use retinyl palmitate, at 25,000 IU per day in the CARET trial and in a bone trial.
- Duration: the effect on retinitis pigmentosa was measured over 4 to 6 years; the large trial in women in Ghana administered 25,000 IU once a week.
- Meals: in the bone trial, vitamin A was taken with the evening meal; no study in this fact sheet compares taking it with or without a meal.
Did you know?
Preformed vitamin A intakes, even just twice the recommendations, may be associated with an increased risk of osteoporosis and hip fractures.
What the studies say
This systematic review and meta-analysis examined the impact of vitamin A supplementation on inflammatory biomarkers in adults. It found that vitamin A supplementation significantly increased plasma C-reactive protein (CRP) concentrations. However, there was no significant correlation with TNF-α, except in the case of chronic hepatitis B where supplementation with retinyl palmitate at 50,000 IU/day decreased TNF-α concentrations. An inverse association between vitamin A supplementation and IL-6 was observed in various infectious conditions.
Gholizadeh M, Basafa Roodi P, Abaj F, Shab-Bidar S, Saedisomeolia A, Asbaghi O, Lak M. — Scientific reports (2022) — View the source study
Pairs well with
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more