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Vitamina A

Also known as: Retinol, Vitamin A, Vitamin A1, Retinoids, Beta-carotene, Retinal, Retinoic acid, Retinyl palmitate, Retinyl acetate

Overview

Vitamin A is a group of fat-soluble retinoids, including retinol, retinal, retinoic acid, and provitamin A carotenoids like beta-carotene. It is an essential nutrient crucial for vision, immune function, and skin health. Retinol is found in animal-derived foods such as liver, fish oils, and dairy, while provitamin A carotenoids are present in plant-based foods like carrots and sweet potatoes. Vitamin A is stored in the liver and plays a vital role in cellular growth and differentiation. Extensive clinical trial data, including randomized controlled trials (RCTs) and systematic reviews, support its efficacy, particularly in reducing mortality and morbidity in children in low-income settings. Supplementation is a well-established intervention to combat deficiency and support overall health.

Benefits

Vitamin A supplementation significantly reduces all-cause mortality in children aged 6 months to 5 years by approximately 24%, as evidenced by meta-analyses of RCTs involving over 215,000 participants. It also reduces morbidity from infectious diseases like measles and diarrhea. Vitamin A improves vision and reduces the incidence of xerophthalmia and night blindness. It supports immune function, reducing the incidence and severity of infections. The benefits are most pronounced in children under 5 years in low- and middle-income countries with vitamin A deficiency. The mortality reduction is clinically significant and consistent across multiple large trials, with effects observed within months of supplementation in deficient populations.

How it works

Vitamin A is critical for maintaining epithelial tissues, vision (as retinal in the visual cycle), and immune system modulation. It supports mucosal integrity, enhancing barrier function against pathogens. Vitamin A modulates T-cell function and antibody responses. Retinoic acid receptors (RARs) and retinoid X receptors (RXRs) regulate gene expression. It is absorbed in the small intestine with dietary fat; bioavailability varies by source, with retinol being more bioavailable than carotenoids. Zinc status also influences vitamin A metabolism, highlighting the importance of adequate micronutrient levels for optimal function.

Side effects

Vitamin A is generally safe at recommended doses, but toxicity can occur with excessive intake. Common side effects are rare at therapeutic doses, but high doses may cause nausea and headache. Uncommon side effects include mild gastrointestinal disturbances. Rare side effects include hypervitaminosis A symptoms such as headache, dizziness, blurred vision, and liver abnormalities. Vitamin A can interact with retinoid medications and certain anticonvulsants. Excessive doses should be avoided during pregnancy due to the risk of teratogenic effects. Careful dosing is required in pregnant women and children, with age-appropriate dosing being essential.

Dosage

The WHO recommends 100,000 IU every 4-6 months for infants 6-11 months and 200,000 IU for children 12-59 months in deficiency areas. Optimal dosage ranges vary by age and deficiency status, with supplementation protocols standardized in public health programs. Chronic intake above 10,000 IU/day in adults may risk toxicity. Doses are typically spaced every 4-6 months for preventive supplementation. Retinyl palmitate or retinyl acetate are preferred for supplementation. Dietary fat is required for optimal absorption, and zinc status influences vitamin A metabolism. It's important to adhere to recommended dosages to avoid adverse effects.

FAQs

Is vitamin A supplementation safe for children?

Yes, when dosed according to WHO guidelines, vitamin A supplementation is safe and effective in reducing mortality and morbidity in children.

Can vitamin A overdose occur?

Yes, chronic excessive intake can cause toxicity. Supplementation should follow recommended doses to avoid adverse effects.

How soon do benefits appear?

Mortality and morbidity reductions can be observed within months in deficient populations receiving vitamin A supplementation.

Does vitamin A improve vision in healthy individuals?

Vitamin A primarily prevents deficiency-related vision problems and does not provide significant benefit in those with adequate vitamin A status.

Research Sources

https://pubmed.ncbi.nlm.nih.gov/38816049/ – This study investigates the impact of vitamin A supplementation on various health outcomes. Further details can be found on PubMed.
https://bmjopen.bmj.com/content/14/5/e078053 – A systematic review and meta-analysis included RCTs comparing vitamin A supplementation vs placebo/no intervention. It found significant reductions in mortality and morbidity across age groups, using Cochrane methodology with GRADE assessment, confirming high certainty evidence. Limitations included heterogeneity in populations but a consistent direction of effect.
https://pubmed.ncbi.nlm.nih.gov/21868478/ – This meta-analysis confirms that vitamin A supplementation reduces mortality and morbidity in children. It is supported by multiple RCTs with adequate control groups and reinforces the role of vitamin A in public health nutrition.
https://www.bmj.com/content/343/bmj.d5094 – A Cochrane systematic review and meta-analysis analyzed 43 RCTs with over 215,000 children aged 6 months to 5 years. It demonstrated a 24% reduction in all-cause mortality and decreased incidence of infectious diseases. The large sample size and rigorous methodology strengthen confidence, though most data are from low-income countries.
https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2025.1496931/full – This article discusses the role of vitamin A in public health, focusing on its impact on immune function and disease prevention. It highlights the importance of vitamin A supplementation in vulnerable populations.