Vitamin A
Alternative Names of Vitamin A: Retinol; Retinal; Retinoic acid; Carotenoids
Vitamin A and Carotenes
Vitamin A is a fat soluble vitamin which requires bile salts and fats for absorption. It is stored in the liver. There are two categories of vitamin A, depending on whether the food source is an animal or a plant. In animal foods, vitamin A is present as retinol (preformed vitamin A, the active form). It is not present as retinol in vegetable foods. Plant sources of vitamin A provide the provitamin A, called carotenoids (yellow orange pigments). They are converted into retinol in the body and then to the other active forms of vitamin A such as retinal and retinoic acid. Carotenes are present in alpha, beta and gamma forms and there are 500 carotenoids; out of which beta carotene is one. Efficiency of conversion of 1 mcg of beta-carotene to active Vitamin A is just 0.5 mcg and other forms of Carotene is much lesser. Only 50% of beta carotene is believed to be absorbed for practical purposes.
Vitamin A in foods is expressed as micrograms of retinol activity equivalents (RAEs) of vitamin A per standard amount, but it is also stated as IU : 0.33 mcg RAEs. Alternatively, 1 mcg = 3.33 IU
Symptoms of Vitamin A Deficiency
Night blindness or failure to adapt to dim light is the most common vitamin A deficiency symptom. Other deficiency symptoms are atrophy and keratinization of epithelium, leading to dry hair and dry skin, increased incidence of ear, sinus, respiratory, urinary, and digestive system infections, inability to gain weight, drying of cornea and ulceration (Xerophthalmia), nervous disorders, and skin sores.
Prolonged ingestion leads to the hypervitaminosis and development of toxicity. This leads to pathogenic changes in bones, skin mucous membranes and liver.
Foods with Vitamin A
Vitamin A rich foods: Retinol is an active form of vitamin A found in animal sources such as liver, kidney, the fat of whole milk, cream, high fat cheeses, cod, halibut fish oil and egg yolk, and some fortified foods. Except for skim milk fortified with Vitamin A, the rest are high in saturated fat and cholesterol.
Richest sources of carotene are yellow / orange and green leafy vegetables like carrots, squashes, pumpkin, broccoli, spinach and most other dark green leafy veggies. Yellow / orange fruits such as cantaloupe, apricots, pink grapefruit are also rich in beta carotene.
The higher the intensity of the color of a fruit or vegetable, the higher is the beta-carotene content. Vegetable sources of vitamin A as beta-carotene are fat and cholesterol-free.
Functions of Vitamin A
- Promotes good vision mainly in dim light. The retina of the eye contains two distinct photoreceptor systems: the rods – sensitive to low intensity light and the cones. Vit. A is a component of these photoreceptor cells. It is needed to produce the pigments in the retina of the eye. The Aldehyde form (retinal) combines with the protein opsin to produce rhodopsin in rods and idopsin in cones and is thus essential for the integrity of photoreception in the retina’s rods and cones.
- It is necessary for growth and development of skeletal and soft tissues, through its effect on protein synthesis and bone cell differentiation (cell growth). It is necessary for development of normal bone, and the enamel forming epithelial cells in the development of teeth.
- It also plays a role in maintaining normal health and vigor of epithelial cell structures, thus maintaining healthy skin and mucous membranes.
- Its potential role in cancer prevention is due the antioxidant properties of carotenoids, for example beta carotene from food sources. Beta carotene supplements do not reduce cancer risk.
- May also play a role in reproduction and lactation.
Health Benefits of Vitamin A
- Promotes good vision mainly in dim light.
- Develops and strengthens bones, teeth, structural cells.
- Maintains healthy skin and mucous membranes.
- Beta carotene, an antioxidant helps in anti-aging due to its free radical scavenging property.
- The antioxidant properties of beta carotene obtained from food sources helps in cancer prevention.
- Likely to help in reproduction and breast feeding.
