Vitamin A – Functions, Deficiency and Daily Needs
Vitamin A is a fat-soluble vitamin essential for vision, immune function, and cell growth. A deficiency can lead to night blindness and increased susceptibility to infections.
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Vitamin A is a fat-soluble vitamin essential for vision, immune function, and cell growth. A deficiency can lead to night blindness and increased susceptibility to infections.
What is Vitamin A?
Vitamin A is a fat-soluble vitamin that the body cannot produce on its own and must therefore obtain through the diet. It exists in two main forms: retinol (preformed vitamin A), which is absorbed directly from animal-based foods, and provitamin A (e.g., beta-carotene), found in plant-based foods and converted into active vitamin A in the body.
Biological Functions
Vitamin A performs numerous vital functions in the human body:
- Vision: Vitamin A is a key component of rhodopsin, the visual pigment required for low-light and night vision.
- Immune system: It supports immune cell function and helps maintain the integrity of mucous membranes as a first line of defense against pathogens.
- Cell growth and differentiation: Vitamin A regulates the development and specialization of cells, particularly in the skin, lungs, and intestines.
- Embryonic development: It plays a critical role in normal embryonic development, especially in organ formation.
- Skin health: Vitamin A promotes skin cell renewal and is widely used in dermatology.
Dietary Sources
Animal Sources (Retinol)
- Liver (particularly rich in vitamin A)
- Fish and fish liver oil (e.g., cod liver oil)
- Milk and dairy products
- Eggs
- Butter
Plant Sources (Provitamin A / Beta-Carotene)
- Carrots, sweet potatoes, and pumpkin
- Spinach, kale, and other dark green leafy vegetables
- Mango, papaya, and apricots
Recommended Daily Intake
The recommended daily intake for vitamin A is expressed in micrograms of retinol activity equivalents (µg RAE). According to the World Health Organization (WHO) and national health authorities, the following reference values apply:
- Adult men: approx. 900 µg RAE/day
- Adult women: approx. 700 µg RAE/day
- Pregnant women: approx. 770 µg RAE/day
- Breastfeeding women: approx. 1,300 µg RAE/day
- Children: 300–600 µg RAE/day (depending on age)
Vitamin A Deficiency
Vitamin A deficiency is one of the most common micronutrient deficiencies worldwide, particularly in developing countries. Common causes include insufficient dietary intake, malabsorption syndromes (e.g., celiac disease, inflammatory bowel disease), and increased demand (e.g., during pregnancy).
Symptoms of Deficiency
- Night blindness (one of the earliest signs)
- Dry eyes (xerophthalmia) and, in severe cases, blindness
- Increased susceptibility to infections
- Dry, scaly skin (hyperkeratosis)
- Growth retardation in children
At-Risk Groups
- Children in developing countries
- Pregnant and breastfeeding women
- People with fat malabsorption disorders
- Individuals with chronic alcohol abuse
Overconsumption and Toxicity
Because vitamin A is fat-soluble, it can be stored in the body, primarily in the liver. Chronic overconsumption (hypervitaminosis A) -- typically due to excessive supplementation -- can be toxic. Symptoms of overdose include nausea, headaches, dizziness, hair loss, liver damage, and, in pregnant women, birth defects in the unborn child. The tolerable upper intake level (UL) for adults, as established by the European Food Safety Authority (EFSA), is 3,000 µg of retinol per day. Beta-carotene from plant sources is considered safe, as the body regulates its conversion to vitamin A based on need.
Supplementation
Vitamin A supplements are available in the form of retinol, retinyl acetate, or retinyl palmitate. Supplementation should only be undertaken in cases of confirmed deficiency or on medical advice. In certain parts of the world, the WHO recommends vitamin A supplementation to prevent deficiency disorders and reduce child mortality from measles.
Interactions
Vitamin A can interact with various medications and nutrients:
- Retinoids (e.g., isotretinoin used in acne treatment): Combining with vitamin A supplements can lead to dangerous overdose levels.
- Vitamin E: May help reduce the toxicity associated with high vitamin A intake.
- Zinc: Zinc is required for the transport of vitamin A in the blood; zinc deficiency can impair vitamin A utilization.
- Cholestyramine and mineral oils: Can inhibit the absorption of fat-soluble vitamins, including vitamin A.
References
- World Health Organization (WHO): Vitamin A supplementation. Geneva, 2022. Available at: https://www.who.int/health-topics/vitamin-a-deficiency
- National Institutes of Health (NIH), Office of Dietary Supplements: Vitamin A -- Fact Sheet for Health Professionals. Bethesda, 2023. Available at: https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/
- European Food Safety Authority (EFSA): Dietary Reference Values for Vitamin A. EFSA Journal, 2015; 13(3):4028.
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Related search terms: Vitamin A + Retinol + Retinal + Retinoic Acid + Provitamin A + Beta-Carotene