Vitamin A (retinol)

Definition: Vitamin A (retinol) is a fat-soluble vitamin that is essential for various physiological functions in the body, including vision, immune function, skin health, and cellular communication. It exists in several forms, with retinol, retinal, and retinoic acid being the most biologically active.

Importance

• Vision: This vitamin is crucial for maintaining healthy vision. It is a component of rhodopsin, a protein in the retina that enables the eye to detect light and is essential for night vision.
• Immune Function: It plays a vital role in maintaining the integrity of epithelial tissues and supports the immune system by promoting the development and differentiation of white blood cells.
• Cell Growth and Development: Vitamin A is involved in cellular differentiation and growth, influencing the development of organs and tissues during embryogenesis.
• Skin Health: It contributes to skin health by promoting cell turnover and repair.

Sources

This vitamin can be obtained from both animal and plant sources:

• Animal Sources: Liver, fish liver oils, dairy products, and eggs are rich in preformed vitamin A (retinol).
• Plant Sources: Carrots, sweet potatoes, spinach, and other leafy greens contain provitamin A carotenoids (e.g., beta-carotene), which the body can convert into retinol.

Deficiency and Toxicity

• Deficiency: Vitamin A deficiency can lead to night blindness, dry eyes, increased susceptibility to infections, and skin issues. Severe deficiency can result in xerophthalmia, a condition that can cause blindness.
• Toxicity: Excessive intake of preformed vitamin A (from supplements or animal sources) can lead to hypervitaminosis A, resulting in symptoms such as nausea, headache, dizziness, and even liver damage.

Conclusion

Vitamin A is essential for numerous bodily functions, particularly in vision and immune health. Ensuring adequate intake through a balanced diet rich in both animal and plant sources is crucial for maintaining overall health.

References

1. Ross AC, et al. “A Vitamin and Carotenoids.” In: Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academies Press; 1997. Available from: https://doi.org/10.17226/5776
2. World Health Organization. “A Vitamin deficiency.” Available from: https://www.who.int/news-room/fact-sheets/detail/vitamin-a-deficiency
3. Blomhoff R, et al. “A Vitamin: metabolism and biological effects.” Nutrition Reviews. 2006; 64(4): 171-178. Available from: https://doi.org/10.1111/j.1753-4887.2006.tb00176.x