Vitamin A is fat-soluble, stored in body fat. Although not necessary to intake every day, Vitamin A is vital to the body. 90% of it is stored in liver. Vitamin A is found in two forms - Retinol (preformed Vitamin A) or Retinoids (beta-carotene).
Beta-carotene is a precursor to Vitamin A, formed in the intestine, liver, and kidneys. Beta-carotene is found in deep-yellow and deep-green leafy vegetables. Vitamin A is found in fish liver oils, egg yolk, liver, and fortified foods such as milk or margarine.
2. What does it do and what scientific studies give evidence to support this?
Vitamin A is required for synthesis of photoreceptor pigments of rods and cones, the integrity of skin and mucosae, normal tooth and bone development; normal reproductive capabilities; and has important antioxidant properties which translate into anticancer and antiatherosclerosis effects. It helps form the substance rhodopsin, which is necessary for good vision (particularly night vision). Vitamin A also helps keep the membranes, inner linings, tissues, the skin, and eyes resistant to infection and in good health. It also helps to energize cells in the immune system and acts as an antioxidant. It helps fight cancer and degenerative diseases as an anti-aging vitamin by absorbing and destroying harmful "free radicals", destructive molecules that interfere with normal cell activities, damage membranes and cells, and lead to cell mutations, and cellular damage. It's a good idea to stop free radicals before they stop you.
3. Who needs it and are there any symptoms of deficiency?
Vitamin A is good for these systems: poor night vision, dry or rough skin, and respitory infections. Symptoms of deficiency are night blindness; epithelial changes; dry skin and hair; skin sores; increased respitory, digestive, urogenital infections; defective tooth enamel; impaired bone growth; drying of conjunctiva; clouding of cornea; in pregnant women, developmental defects of the embryo. Blacks and Hispanics are both at higher risk of deficiency.
4. How much should be taken? Are there any side effects?
The RDA for males is 5000 IU (1.5mg), females 4000 IU. Vitamin A in excess of 50,000 IU can be toxic, causing damage in the body. Stick to the RDA and you'll better off than if you take to much or too little. Beta-Carotene is not toxic even in large doses because the body converts only what it needs to Vitamin A. The optimal level of Beta-Carotene intake is 17,500 IU. Drug interactions include: reduced effectiveness of Phenytoin and increasing effects of Oral anticoagulants.
Also, check out our multi-vitamin products with many that contain VItamin A.