Vitamin A Importance

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                            Vitamins


Vitamins are essential nutrients for the human body growth and development although these are required in small amount, but have important and specific functions such as promoting growth, reproduction and the maintenance of health. As they cannot be synthesized by the body in large enough amount to support the biological functions performed by our body.

Vitamins are classified into two groups based on their chemical composition are: 

1. Fat soluble vitamins (Hydrophobic)- Vitamin A,Vitamin D, Vitamin E & Vitamin K found in oils and fats.
2. Water-soluble vitamins (hydrophilic)- Vitamin B complex & Vitamin C found in watery part of the food.
Note:- Vitamins do not give you energy. 
                                                                Vitamin A
What is Vitamin A?
Vitamin A is a fat soluble vitamin. There are different forms of vitamin A including retinol, retinal, retinoic acid, and retinyl ester  which are collectively referred to
as  retinoids. The most common form of Vitamin A is retinol.
Occur in the precursor form as beta carotene.

What are the functions of Vitamin A?
Vitamin A having very important functions for our body are:

1. VisionCell 
2. Differentiation of epithelial cells
3. Immunity and growth.
Function of Vitamin A As Vision
Vitamin A is required for the production of rhodopsin (A light sensitive material in the rods of retina.)
-          Retinal turns visual light into nerve signals in retina of eye
-          Retinoic acid required for structural components of eye

Function of Vitamin A : Cell Differentiation
Retinoic acid is necessary for cellular differentiation
Retinoic acid influences production, structure and functions of epithelial cells that line the outside (skin) and external passages (mucous forming cells) with in the body.

Function of Vitamin A : Immunity and growth
Vitamin A is important for embryo development, gene expression
Deficiency leads to decreased resistance to infections

Breast cancer – studies have found a link between
high dietary intake of vitamin A and a reduced risk of
breast cancer among pre-menopausal women with a
family history of breast cancer.


 Deficiency of vitamin A causes :

- Night Blindness
- Dry skin, dry mucous membrane
- Decreased epithelial cell growth
- Xerophalmia (Have difficuilty in producing tears)
- Anaemia
- Hypovitaminosis A

Too much intake of vitamin a may cause :
-          headache , Vomitting, nausea, Abnormal vision, loss of hair
Vitamin A poisoning : A bizarre case of extreme vitamin A poisoning was reported by artic explorers who killed and ate a polar bear. Those who ate the liver become very ill and three of them lost patches of skin, later scientists discovered that 0.25 lb of the liver contains 2.5 yrs worth vitamin A for humans.

Fat soluble Vitamins VS water soluble vitamins
Too much water soluble vitamins that is too much intake of vitamin B and Vitamin C is alright as it comes out in the urine but in case of,
Fat soluble vitamins that is vitamin- A, D, E & K , it cause sickness because it doesn’t dissolve in your urine readily and get stored in your body
That’s why large intake of vitamin A can cause harm and toxic to your body.


What are the sources of vitamin A?
The best dietary sources of vitamin A include eggs, milk, butter, meat, animal liver and fish liver oils example cod and halibut (the liver stores retinol – vitamin A).
Milk- Fortified milk
Carrots etc.

How do we get vitamin A ?
2 chemicals : retinoid and cortenocoids
- Retinoid : Body can use right away
- Cortenocoid : Body can change it into retinoid.hich 

Conversion of carotenoids to retinoids
Enzymatic conversion of carotenoids occus in liver or intestinal cells, forming retinal and retinoic acid
Provitamin A cartenoids
-          Beta –carotene
-          Alpha-carotene
-          Beta- carotene
Other cartenoids
Lutein, Lycopene, zeaxanthin.

Absorption of vitamin A ?
In retinoids when retinyl ester broken down to free in small intestine require bile, digestive enzyme, itegration into micelles.
Once absorbed m retinyl esters reformed in intestinal cells. 90% of retinoids can be absorbed
Carotenoids : Absorbed intact , absorption rate is much lower in this case.
Intestinal cells can convert carotenoids to retinoids.

Where does the Vitamin A is transported and stores ?
Liver stores the 90% of vitamin A in the body and reserves in adequate for several months
Transported via chylomicrons from Intestinal cells to the liver and then from liver it transported to the target tissue as retinol via retinol-binding protein, which is bound to transthyretin.

Where does these retnoids protein present ?
Target cells contains cellular retinoids binding proteins
Directs retinoids to functional site within the cells
Protect retinoids from degradation 






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