How does vitamin A work?

Vitamin A is an essential nutrient that plays an important role in many bodily functions, including:

Vision: Vitamin A is necessary for night vision and vision in low light conditions. It helps the eye produce rhodopsin, a protein used to detect light.
Growth and development: Vitamin A is important for the growth and development of bones, muscles and tissues.
Reproduction: Vitamin A is necessary for reproduction.
Immune system: Vitamin A helps the immune system function properly.
Vitamin A is found in two main forms: retinol and carotenoids. Retinol is the active form of vitamin A and is found in foods of animal origin, such as milk, yogurt, eggs and liver. Carotenoids are precursors to vitamin A and are found in plant-based foods, such as orange, yellow, and dark green fruits and vegetables.

The recommended daily intake (RDI) of vitamin A for adults is 700 micrograms (mcg) for women and 900 mcg for men.

Symptoms of vitamin A deficiency include:

Night blindness: Inability to see in low light.
Xerophthalmia: Dry eyes.
Dry skin: Flaky, cracked skin.
Infection: Increased risk of infection.
Excess vitamin A can be toxic. Symptoms of vitamin A toxicity include:

Headaches
Fatigue
Joint pain
Jaundice
Nausea
Vomiting
Damage to the liver
It is important to get enough vitamin A from your diet, but it is also important to avoid too much.