Vitamin A is required by the retina of the eye for its light-absorbing molecule retinal. This enables the eye to see both low–light and color vision. Vitamin A is also required as an oxidized form of retinol (retinoic acid), an essential hormone-like growth factor for epithelial and other cells in the body.
Vitamin A is found in two dietary forms.
- Retinol: absorbed when eating animal food sources
- The carotenes: alpha-carotene, beta-carotene, gamma-carotene – found in vegetables
Vitamin A: Functions in the Human Body
Vitamin A plays a role in the function of vision, immunity, bone metabolism, haematopoiesis, skin health, antioxidant activity and gene transcription. The Vitamin A role in improving vision is where the commonly cited theory that carrots increase your ability to see arises from. The beta-carotene found in carrots improves eyesight by contributing to the production of Vitamin A levels in the body.
Vitamin A: Recommended Daily Intake (RDI)
Males generally require more vitamin A than females and breastfeeding mothers need twice the female RDI:
- Infants: 500 mcg
- Ages 1 to 3: 300 mcg
- Ages4 to 8: 400 mcg
- Ages 9 to 13: 600 mcg
- Ages 14 to Adult, Male: 900 mcg
- Ages 14 to Adult, Female: 700 mcg
- Breastfeeding Mothers: 1,300 mcg
Liver was used to cure symptoms of vitamin A deficiency long before the term vitamin A was realized, and beef liver still remains the best source of vitamin A. Deficiency is not as common as it historically has been because many everyday foods contain high levels of vitamin A, including milk, eggs, butter, cheese, carrots, spinach, broccoli.
Vitamin A: Risk of Overdose
Vitamin A is a fat-soluble vitamin and therefore has a higher rick of overdose due to toxicity than water soluble vitamins like vitamin C. Fat soluble vitamins are stored in the body unlike water soluble vitamins which are passed by the body. Overdosing on vitamin A can cause “hypervitaminosis A,” which cause osteoporosis amongst other nervous disorders. As a guideline, adults shouldn’t consumer over 2,800 mcg per day and children no more than 900mcg.