On the mention of vitamin A (retinol), what flows through the mind of many is good vision. But vitamin A, though important for good vision, has other health benefits.
Vitamin A (retinol) is a fat soluble vitamin that is essential (i.e. can't be synthesize) for human. Human and animals that can't synthesize vitamin A rely on vitamin A rich diets as their source of vitamin A. Vitamin A has anti-oxidant properties.
Vitamin A deficiency is rare this is because vitamin A is a fat soluble vitamin A, hence can be stored by in the body unlike water soluble vitamin C and B vitamins which can't be stored in the body.
Vitamin A has three active forms (retinal, retinol and retinoic acid). In foods of animal origin vitamin A is in the form of retinyl ester (primarily as retinyl palmitate). While in plant foods it occur as carotenes (beta, alpha, and gamma carotene) which can be converted to the active form.
Since vitamin A can be stored in the body, its daily intake is not really necessary, though a daily intake is still encouraged. As a fat soluble vitamin that can be stored by the body, vitamin A can reach toxic level easily. Vitamin A toxicity is usually associated with high intake of its supplements.
Vitamin A very important for good sight (or good vision), in fact on most food labels, presence of vitamin A is indicated with the symbol of an eye with letter 'A' on it. Vitamin A has many other benefits aside its good works on the eye.
Some health benefits of vitamin A include:
1. Good vision
As known by many vitamin A (retinol) is important for good vision. The retina of the eye requires vitamin A (retinol) in the form retinal which combines with protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light and color vision.
In vitamin A rich diets of animal origin, the major form of vitamin A is an ester, primarily retinyl palmitate, which is converted to retinol in the small intestine. The retinol form functions as a storage form of the vitamin, and can be converted to its visually active aldehyde form; retinal.
In the eye, retinal (11-cis-retinal) is bound to protein "opsin" to form rhodopsin in rods and iodopsin (cones) at conserved lysine residues. As light enters the eye, the 11-cis-retinal is isomerized to the all-"trans" form. This isomerization induces a nervous signal along the optic nerve to the visual center of the brain. The all-"trans" retinal dissociates (i.e. separates) from the opsin through photo-bleaching.
After separating from opsin, the all-"trans"-retinal is recycled and converted back to the 11-"cis"-retinal form by a series of enzymatic reactions. In addition, some of the all-"trans" retinal may be converted to all-"trans" retinol form and then transported with an inter-photoreceptor retinol-binding protein (IRBP) to the pigment epithelial cells. Further esterification into all-"trans" retinyl esters allow for storage of all-trans-retinol within the pigment epithelial cells to be reused when needed. The final stage is conversion of 11-cis-retinal will rebind to opsin to reform rhodopsin (visual purple) in the retina. Rhodopsin is needed to see in low light (contrast) as well as for night vision.
Regeneration of rhodopsin only occurs when retinal is attached to retinal pigmented epithelium. Hence a deficiency in vitamin A will inhibit the reformation of rhodopsin and lead to one of the first symptoms, night blindness.
2. Improves immunity
Vitamin A (retinol) improves the body’s immunity against infections by increasing the lymphocytic responses against disease-causing antigens. It makes the mucus membranes to remain moist to ensure better immunity and also enhances the activity of white blood cells.
It also helps to fight the infections once the germs enter body system.
3. Strong bones and teeth
Vitamin A strengthens the bones and teeth. Because it (Vitamin A) helps in the formation of dentin, a layer of hard material just below the surface of the teeth, thereby enhancing its strength.
4. Good for healthy skin and Prevents Acne
Vitamin A (retinol), in the form of retinoic acid, appears to maintain normal skin health by switching on genes and differentiating keratinocytes (immature skin cells) into mature epidermal cells. Vitamin A is essential for the proper maintenance of the skin tissues and mucus membrane. When mucus membranes are healthy, they are moist and are resistant to cell damage. The moistness inhibits bacteria and viruses entrance.
Vitamin A (retinol) helps to reduce excess sebum production, thus reducing the risk of acne.
13-cis retinoic acid (isotretinoin) is the most prescribed retinoid drug for ance treatment. It reduces the size and secretion of the sebaceous glands. 13-cis retinoic acid (Isotretinoin) reduces bacterial numbers in both the ducts and skin surface. This is thought to be a result of the reduction in sebum, a nutrient source for the bacteria.
It also (13-cis retinoic aci or Isotretinoin) reduces inflammation via inhibition of chemotactic responses of monocytes and neutrophils. Isotretinoin has been shown to initiate remodeling of the sebaceous glands, thus triggering changes in gene expression that selectively induce apoptosis.
5. Fights certain cancer
Because of it anti-oxidant properties, vitamin A fights cancer. It inhibit the production of DNA in cancerous cells. It slows down tumor growth in established cancers and may keep leukemia cells from dividing.
Sources of vitamin A
Foods rich in vitamin A, are widely available. Hence I will say that vitamin A is inexpensive. Some food sources of vitamin A include:
Carrot
Fish liver oils
Egg yolk
Beef liver
Cheddar cheese
Fortified milk
Kale
Spinach
Pumpkin
Sweet potatoes
Deficiency symptoms of vitamin A
Vitamin A deficiency could be primary or secondary. The primary deficiency is mainly as a result of not have enough vitamin A in diets. While secondary deficiency is as a result of the body inability to absorb the vitamin.
Symptoms of vitamin A deficiency include:
Night blindness
A burning sensation or itching in the eye
keratinization of the skin
Inflammation of the eyelids
Xerophthalmia (dryness of the conjunctiva)
Dull lusterless hair dandruff
Brittle nails that break easily
Sexual disorders
Precancerous changes in the body tissues
Fatigue
Insomnia and depression.
Reference:
http://health.howstuffworks.com/wellness/food-nutrition/vitamin-supplements/benefits-of-vitamin-a.html
https://en.m.wikipedia.org/wiki/Vitamin_A
https://www.organicfacts.net/health-benefits/vitamins/health-benefits-of-vitamin-a-or-retinol.html
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