Vitamin A: Retinol and Carotenes

What Does Vitamin A Do and Why is it Important?

Vitamin A was discovered in based on research going back to 1906. The research indicated that factors other than fats, carbohydrates, and proteins were necessary for farmers to consider in order to keep their cattle healthy. In 1917, one of the additional factors was discovered by Elmer McCollum at the University of Wisconsin—Madison, and Lafayette Mendel and Thomas Burr Osborne at Yale University. Vitamin A was actually discovered after Vitamin B, but since Vitamin B was water-soluble and Vitamin A was fat-soluble the researchers decided to give the fat soluble factor A the name Vitamin A.

The Two Major Forms of Vitamin A

There are two principal forms in food. The first is retinol. This form of Vitamin A is absorbed in the human body when eating animal food sources. It is a yellow, fat-soluble substance. Retinol is an alcohol which is produced in the small intestine. Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinol ester. The second form is carotenes. All forms of Vitamin A have a beta-ionone ring to which an isoprenoid chain is attached called a retinyl group. Alpha-carotene, beta-carotene, gamma-carotene; and the xanthophylls beta-cryptoxanthin function as Vitamin A in herbivores and omnivore animals.

Why is Vitamin A Important?

Vitamin A plays many roles in the human body. Vitamin A is important for the human health of: vision, gene transcription, immune function, embryonic development and reproduction, bone metabolism, haematopoiesis, skin health, and antioxidant Activity.

Vision

Vitamin A is essential for both scotopic and color vision. The retina of the eye needs Vitamin A in the form of a specific metabolite, the light-absorbing molecule retinal. Through the conversion of retinal the retina will refine rhodopsin. Rhodopsin is needed to see black and white as well as necessary for the human eye to see anything at night. That is the reason that a deficiency of Vitamin A will lead to night blindness.

Dermatology

The maintenance of skin health appears to be another benefit of Vitamin A:Retinol and Carotenes. There is research which supports the use of isotretinoin for the treatment of acne. The mechanism of action remains unknown; however, when applied to the human skin it drastically reduces the size and secretion of the sebaceous glands. Isotretinoin reduces bacterial numbers in both the ducts and skin surface. By reducing the number of bacteria it is thought to also reduce the amount of sebum, a nutrient source for the bacteria. While the research behind this finding is still very new, the use of Vitamin A Carotene to fight acne seems to be headed in the right direction.

Natural Sources of Vitamin A

There are many foods where Vitamin A can naturally be found: liver (beef, pork, chicken, and fish), carrots, broccoli, sweet potatoes, kale, butter, spinach, pumpkin, collard greens, cheddar cheese, cantaloupe melon, egg, apricot, papaya, mango, pea, broccoli leaf, and milk. The amount of Vitamin A a person is able to absorb from these different natural sources will depend on the person’s metabolic rate and the bioavailability of the food sources.

How Much Vitamin A Can Be Absorbed from Different Sources?

There is new research which indicates that fruits and vegetables are not as useful for obtaining Vitamin A as was once thought. The amounts of Vitamin A which the human body was thought to get from fruit and vegetables were far lower compared to the Vitamin A a person would get from animal sources of fat-dissolved oils and supplements. This new research is very important for Vegetarians; because many countries were little meat or Vitamin A fortified foods are available there is a huge number of reported night blindness. The Food and Nutrition Board has published a sampled diet, for a single day, which provides sufficient Vitamin A for a person; however, with the new research involving Vitamin A it is important for both Vegetarians and Vegans to know how much Vitamin A they are really absorbing from the foods they eat.

Supplementing the Vitamin A in Your Diet

With the importance of Vitamin A for the health of the human body it is important for people to get the proper amount in their daily diet. The FDA has produced a table which shows the proper amount of Vitamin A a person should get based on their own personal life stage. A person needs to monitor the proper amount of Vitamin A they take in each day. If a person is lacking the proper amount of Vitamin A then it would be wise to consider taking a good multivitamin which contains proper levels of Vitamin A for their own personal body type. This means that men and women will need different levels of Vitamin A, so therefore it would be wise to find a good gender specific multivitamin to take to get the proper amount.

Proper research about dieting and supplements should be performed before taking any vitamin or mineral, but finding a good well established brand of multivitamins is a good first step for a person towards personal health.

Click to see known causes of Vitamin A Deficiency.

See Also:

• Vitamin B Complex
• Vitamin C Ascorbic Acid
• Vitamin D