Vitamins - VITAMIN A and CAROTENOIDS

VITAMIN A and CAROTENOIDS - What are they good for?

Darrell Miller

06/09/05

Date: June 09, 2005 09:27 AM
Author: Darrell Miller (dm@vitanetonline.com)
Subject: VITAMIN A and CAROTENOIDS - What are they good for?

Vitamins

In 1912, Casimir Funk coined the term 'vitamine' to refer to a 'vital factor' he proposed was an essential component present in foods. His conjecture dovetailed with other research, leading to the isolation in the 1930's and 40's of the compounds we now call vitamins.

Vitamins are chemical substances which play a variety of roles in the human body. They are core components of any nutritional supplementation program.

While many people are aware of vitamins as necessary substances for good nutrition, few have a grasp of the extraordinary complexity of the roles they play in our bodies. As you'll see below, vitamins are involved in trillions of biochemical interactions every minute to keep us alive and functioning. For example, B-vitamins are converted into coenzymes which are directly necessary for the production of ATP energy from food, a process that goes on continuously in every cell in the body and which in turn fuels myriad physiological events such as muscle contraction, brain activity or tissue repair.

Source Naturals offers a full line of vitamins in bioactive forms, allowing you to tailor a nutritional supplementation plan to your individual needs.

VITAMIN A and CAROTENOIDS

Vitamin A

Vitamin A is a generic term for a class of fat-soluble substances called retinoids, which can either be consumed preformed or synthesized by the liver from plant pigments called carotenoids (see 'Carotenoids', below). An essential nutrient, vitamin A is perhaps best known for its role in vision.

The outer segments of the rods, a type of light-sensitive cell in the retina of the eye, contain a pigment called rhodopsin (or 'visual purple') that mediates vision in dim light. Cone cells mediate color vision via three additional pigments. Both rods and cones are surrounded by pigmented epithelial cells that store vitamin A. Rhodopsin is formed from a protein called opsin and a vitamin A-dependent compound called 11-cis retinal. As light strikes the rods and cones it is absorbed by the pigment molecules, and retinal is split off from opsin. This chemical change allows an electrical impulse to be sent to the optic nerve and thus to the brain. The pigment must then be regenerated from opsin and retinal. Repeated small losses of retinal during this process require a constant replenishment of vitamin A to the eyes.

Vitamin A also plays an extremely important role in epithelial cell differentiation. Cell differentiation is the process by which a cell undergoes a change to a specialized cell type, allowing it to perform particular functions in the body. It is not yet understood precisely how vitamin A is involved in this process. One hypothesis is that it directly affects gene expression through its interaction with chromatin, a complex of DNA, RNA and protein in the cell nucleus. These interactions affect the process of transcription of DNA to messenger RNA, leading to synthesis of a specific group of cellular proteins.

Each one of us carries in our DNA a unique genetic blueprint. This genetic material is the same in every cell of our bodies. It is only because of this mysterious and magical process of differentiation that we have specialized cell types - and therefore eyes, ears, lungs and hearts.

Vitamin A is necessary, either directly or indirectly, for the healthy growth and functioning of many of our tissues and organ systems, including the eyes, the skin, the bones, the reproductive system, and the natural defenses. It is not yet known whether this requirement is due to the role of vitamin A in cell differentiation or whether there are other physiological processes for which vitamin A is essential.

Carotenoids

Vitamin A is related to a class of nutrients called carotenoids, including alpha and beta carotene, lycopene and lutein. Carotenoids are botanical pigments whose colors range from red to orange to yellow. Some carotenoids, particularly beta carotene, can be converted into vitamin A predominantly in the intestinal mucosa and to some extent in the liver. Carotenoids are completely non-toxic; their conversion into vitamin A is well-regulated by the body, making them extremely safe sources of this essential nutrient.

In addition to their role as safe sources of vitamin A, carotenoids are powerful nutrients in their own right. Their primary claim to fame is their powerful antioxidant action, particularly against singlet oxygen. Singlet oxygen is an 'excited' ion of oxygen which, while not technically a free radical, is nonetheless highly reactive. It causes 'oxidative' reactions which can impair or destroy membranes, enzymes and DNA. It can also lead to the formation of free radicals which can cause additional damage.

Certain carotenoids such as beta carotene, because of their chemical structure, can neutralize singlet oxygen by absorbing its extra energy and dissipating it throughout the carotenoid molecule, releasing the energy as heat and converting the singlet oxygen back to 'normal' oxygen. One molecule of beta carotene can quench up to 1000 molecules of singlet oxygen.

In addition to their role as singlet oxygen quenchers, carotenes provide antioxidant protection against free radicals as well. In nature, they protect plants from photo-oxidative reactions; in humans, certain carotenoids, notably beta carotene, may help protect the skin from such reactions. Other carotenoids may provide more localized protection to particular organs. Lutein and zeaxanthin, for example, are selectively concentrated in the retina of the eye. Along with vitamins C and E, carotenes are among the most important nutrient antioxidants in the human body.

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