Retinol, dairy products, fish, and meat.
A portion of the vitamin A in some supplements is in the form of beta-carotene and the remainder is preformed vitamin A; others contain only preformed vitamin A or only beta-carotene. Supplement labels usually indicate the percentage of each form of the vitamin. The amounts of vitamin A in stand-alone supplements range widely [ 2 ]. Multivitamin supplements typically contain 2,500–10,000 IU vitamin A, often in the form of both retinol and beta-carotene. About 28%–37% of the general population uses supplements containing vitamin A [ 9 ]. Since this is the form of vitamin A used by the body, it is added to our stores of vitamin A right away. On the other hand, beta carotene is derived from plant foods and needs to be converted by the body into retinoids before it can be used. Since vitamin A is fat-soluble it is not needed in daily, large quantities. Fat-soluble vitamins are stored in the body in organs such as the liver. Most of the vitamin A that we consume goes to the liver to be stored until it is needed by another part of the body. Vitamin A is a fat-soluble vitamin that has several important functions in the body. 1  It helps cells reproduce normally, a process called cellular differentiation. 2  It is essential for good vision. 3  It is needed for the proper development of an embryo and fetus. Overview. Vitamin A is a fat-soluble vitamin that has several important functions in the body. 1  It helps cells reproduce normally, a process called cellular differentiation. 2  It is essential for good vision. 3  The first sign of a vitamin A deficiency is often poor sight at night. Two forms of vitamin A are available in the human diet: preformed vitamin A (retinol and its esterified form, retinyl ester) and provitamin A carotenoids [ 1-5 ]. Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat (especially liver). By far the most important provitamin A carotenoid is beta-carotene; other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin. The amounts of vitamin A in stand-alone supplements range widely [ 2 ]. Multivitamin supplements typically contain 2,500–10,000 IU vitamin A, often in the form of both retinol and beta-carotene. About 28%–37% of the general population uses supplements containing vitamin A [ 9 ]. 1 Retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance. 2  Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinyl ester. 3  It is also commercially produced and administered as esters such as retinyl acetate or palmitate. Vitamin A, in the retinoic acid form, plays an important role in gene transcription. Once retinol has been taken up by a cell, it can be oxidized to retinal (retinaldehyde) by retinol dehydrogenases and then retinaldehyde can be oxidized to retinoic acid by retinaldehyde dehydrogenases. Vitamin A can be found in two principal forms in foods 1  : Retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance. 2  Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinyl ester. Vitamin A, in the retinoic acid form, plays an important role in gene transcription. Once retinol has been taken up by a cell, it can be oxidized to retinal (retinaldehyde) by retinol dehydrogenases and then retinaldehyde can be oxidized to retinoic acid by retinaldehyde dehydrogenases. The vitamin A that we obtain from animal products is called retinoids and can be used by our bodies without any modification. The form of vitamin A found in fruits and vegetables is known as carotenoids. The most common type of carotenoid is-carotene (beta carotene). These carotenoids are used to build the type of vitamin A used by our body. Vitamin A is important to vision and the growth of the bones. Since vitamin A is fat-soluble it is not needed in daily, large quantities. Fat-soluble vitamins are stored in the body in organs such as the liver. Most of the vitamin A that we consume goes to the liver to be stored until it is needed by another part of the body. In foods of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to retinol (chemically an alcohol) in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to and from its visually active aldehyde form, retinal. Vitamin A, in the retinoic acid form, plays an important role in gene transcription. Once retinol has been taken up by a cell, it can be oxidized to retinal (retinaldehyde) by retinol dehydrogenases and then retinaldehyde can be oxidized to retinoic acid by retinaldehyde dehydrogenases. Retinoids: These medications are a synthetic form of vitamin A and are sometimes prescribed in high doses. People who take retinoids should not take additional vitamin A supplements. In addition, these drugs can cause severe birth defects. Overview. Vitamin A is a fat-soluble vitamin that has several important functions in the body. 1  It helps cells reproduce normally, a process called cellular differentiation. 2  It is essential for good vision. 3  The first sign of a vitamin A deficiency is often poor sight at night. Vitamin D supplements are available in two forms: vitamin D2 and vitamin D3. The D3 form is more active than the D2 form and a better choice when choosing a supplement. Dosage levels range from 400 to 5,000 I.U. 
http://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/ http://www.myfooddiary.com/Resources/nutrient_facts/nutrient_vitaminA.asp http://umm.edu/health/medical/altmed/supplement/vitamin-a-retinol http://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/ https://en.wikipedia.org/wiki/Vitamin_A https://en.wikipedia.org/wiki/Vitamin_A http://www.myfooddiary.com/Resources/nutrient_facts/nutrient_vitaminA.asp https://en.wikipedia.org/wiki/Vitamin_A http://umm.edu/health/medical/altmed/supplement/vitamin-a-retinol https://www.sharecare.com/health/vitamin-d/what-form-vitamin-should-take
what form should vitamin a be in