Vitamin A

Vitamin A is a group of fat-soluble retinoids, including retinol, retinal, retinoic acid, and several provitamin A carotenoids, the most noted being beta-carotene. The vitamin plays a critical role in maintaining healthy vision, neurological function, and skin health.

The body converts provitamin A carotenoids into preformed vitamin A. However, not all provitamin A carotenoids are created equal. Some, such as beta-carotene, are converted more efficiently than others.

The recommended daily intake (RDI) of vitamin A for adults is 900 micrograms (mcg) for men and 700 mcg for women. Pregnant women need 770 mcg of vitamin A per day, and breastfeeding women need 1,300 mcg per day.

Here are some detailed insights on Vitamin A:

1. Vision: Vitamin A is essential for good vision. The retinol form is converted into the light-absorbing molecule retinal during the visual cycle. This is crucial for both low-light (also called scotopic) and color vision. A deficiency in vitamin A can lead to night blindness, a condition that may result in an inability to adapt to darkness.
2. Immune System: Vitamin A plays a critical role in maintaining the health of the immune system. It helps form and maintain the health of skin and mucous membranes, which act as the body’s first line of defense against pathogens. Also, it’s involved in the production and function of white blood cells, which help capture and clear bacteria and other pathogens from the bloodstream.
3. Cell Growth and Differentiation: Vitamin A is necessary for the growth and specialization of many types of cells in the body. This includes the cells lining the digestive tract, lungs, skin, and those in the immune system. The role of vitamin A in the healthy growth of cells has implications for reproduction and embryonic development, too.
4. Skin Health: Vitamin A is often used in topical creams to treat skin conditions like acne and psoriasis due to its role in regulating skin growth and differentiation.
5. Sources: Vitamin A can be found in two primary forms: preformed vitamin A (also known as retinol, found in foods from animal sources) and provitamin A (found in plant-based foods). Preformed vitamin A is found in foods like liver, fish, and dairy products, while provitamin A is found in fruits, vegetables, and other plant-based products, especially those that are red, orange, and yellow.
6. Deficiency: A deficiency of vitamin A can lead to a range of problems. As mentioned, night blindness is a common symptom, but prolonged deficiency can lead to complete loss of vision. Skin can become dry and hardened, and the immune system can be compromised, leading to an increased risk of infections. In severe cases, vitamin A deficiency can lead to death.
7. Toxicity: Although vitamin A is essential for health, an excess intake (hypervitaminosis A) can be harmful and can lead to nausea, irritability, anorexia (reduced appetite), vomiting, blurry vision, headaches, hair loss, muscle and abdominal pain, and weakness, and in severe cases, it can lead to serious health problems like liver damage and increased pressure in the brain. This is usually a concern with supplements rather than food sources of the vitamin.