Vitamin A Functions and Benefits
Vitamin A plays essential roles in vision, epithelial cell maintenance, immune function, reproduction, growth, and development. 1 This fat-soluble vitamin is crucial for multiple physiological processes that directly impact morbidity, mortality, and quality of life.
Key Functions of Vitamin A
Vision
- Critical component of the visual system
- Essential for normal vision, particularly night vision
- Deficiency can lead to night blindness 1
Epithelial Cell Maintenance
- Maintains integrity and differentiation of epithelial cells throughout the body
- Supports skin health and barrier function
- Promotes wound healing by:
- Stimulating epidermal turnover
- Increasing re-epithelialization
- Enhancing production of extracellular matrix components (collagen type I and fibronectin)
- Increasing proliferation of keratinocytes and fibroblasts 2
Immune Function
- Enhances immune response and T-cell function
- Reduces morbidity from infections including respiratory infections
- Critical for maintaining adequate immune function
- Known as an "anti-inflammation vitamin" due to its role in immune regulation 1, 3
Growth and Development
- Essential for proper embryological development
- Supports normal growth patterns
- Involved in cell differentiation and morphogenesis 1, 4
Gene Regulation
- Functions through nuclear retinoic acid receptors
- Regulates hundreds of genes through retinoid X receptors and peroxisome proliferator-activated receptors
- Controls cell differentiation and proliferation 2, 5
Clinical Applications and Benefits
Respiratory Health
- Prophylactic supplementation protects against bronchopulmonary dysplasia
- Reduces requirement for oxygen support in premature infants 1
Wound Healing
- Reverses inhibitory effects of anti-inflammatory steroids on wound healing
- Decreases levels of degrading matrix metalloproteinases
- Promotes tissue repair 2
Immune System Support
- Enhances immune response against infections
- May reduce morbidity from measles and respiratory infections 5, 3
Deficiency Risks
Vitamin A deficiency can lead to:
- Night blindness and vision problems
- Impaired epithelial integrity
- Increased susceptibility to infections
- Growth retardation
- Reproductive issues
- Xerophthalmia and blindness (in severe cases) 4, 5
Recommended Intake
For parenteral nutrition:
- Preterm infants: 700-1500 IU/kg/day (227-455 μg/kg/day)
- Term infants: 150-300 μg/kg/day (2300 IU/697 μg per day)
- Older children: 150 μg/day 1
For oral intake in adults:
- Men: 1000 μg retinol equivalents (RE)
- Non-pregnant and pregnant women: 800 μg RE
- Lactating women: 1300 μg RE 5
Important Considerations
Administration
- When given parenterally, vitamin A should be administered with lipid emulsion to prevent substantial losses from photo-degradation and adsorptive loss 1
- Total delivery of retinol from parenteral infusions can be below 40% of intended dose due to adsorption onto tubing materials 1
Risk Factors for Deficiency
- Infection (sepsis, HIV)
- Burns
- Mechanical ventilation
- Steroid use
- Hepatobiliary dysfunction
- Renal failure
- Trauma
- Hematooncological conditions
- Intestinal dysfunction
- Protein-energy malnutrition
- Zinc deficiency
- Cystic fibrosis 1
Monitoring
- Serum concentrations below 200 mg/l (0.7 mmol/l) indicate deficiency in premature infants
- Concentrations below 100 mg/l (0.35 mmol/l) indicate severe deficiency
- Normal range for children older than 6 months and adults: 300-800 mg/l (1.05-2.8 mmol/l) 1
Vitamin A's diverse functions make it critical for maintaining health and preventing disease across multiple body systems, with particularly important roles in vision, epithelial integrity, and immune function.