Vitamin A is an essential human nutrient. It may be found in any of these forms:
Retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin with importance in vision and bone growth, it belongs to the family of chemical compounds known as retinoids.
Other retinoids, a class of chemical compounds that are related chemically to vitamin A, are used in medicine.
Carotenoids or other substances that enable the body to synthesize retinoids. Carotenoids are organic pigments that are naturally occurring in plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria.
Health benefits of vitamin A
Vitamin A is a group of compounds that play an important role in vision, bone growth, reproduction, cell division, and cell differentiation (in which a cell becomes part of the brain, muscle, lungs, blood, or other specialized tissue.) .Vitamin A helps regulate the immune system, which helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses Vitamin A also may help lymphocytes (a type of white blood cell) fight infections more effectively.
Vitamin A promotes healthy surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, it becomes easier for bacteria to enter the body and cause infection. Vitamin A also helps the skin and mucous membranes function as a barrier to bacteria and viruses.
Fortified foods such as fortified breakfast cereals also provide vitamin A.
Provitamin A carotenoids are abundant in darkly colored fruits and vegetables
Vitamin A is contained in fortified breakfast cereals, whereas major contributors of provitamin A carotenoids are carrots, cantaloupes, sweet potatoes, and spinach.
Recommended Dietary Intake for Vitamin A (Retinol) daily values:
[code]Age Vitamin A (Retinol) (mcg/day)
0 to 6 months 400
7 - 12 months 500
1 to 3 years 300
4 to 8 years 400
9 to 13 years 600
14 to 51+ years 900
9 to 13 years 600
14 to 51+ years 700
Tolerable Upper Intake Levels (ULs) for Vitamin A(retinol).
Taking amounts higher than those listed below is dangerous for heath.
Beta Carotene taken from vegetable sources don’t have an Upper Intake Level limit.
Age Children Males Females Pregnancy Lactation
(years) (mcg) (mcg) (mcg) (mcg) (mcg)
14-18 2,800 2,800 2,800 2,800
19+ 3,000 3,000 3,000 3,000
Vitamin A deficiency.
Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt, it was known that night blindness could be cured by eating liver, which was later found to be a rich source of the vitamin. Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea.
Vitamin A deficiency diminishes the ability to fight infections. In countries where such deficiency is common and immunization programs are limited, millions of children die each year from complications of infectious diseases such as measles In vitamin A-deficient individuals, cells lining the lungs lose their ability to remove disease-causing microorganisms. This may contribute to the pneumonia associated with vitamin A deficiency
Important to Know
Vegetarians who do not consume eggs and dairy foods need provitamin A carotenoids to meet their need for vitamin A. They should include a minimum of five servings of fruits and vegetables in their daily diet and regularly choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A.
What are the health risks of too many carotenoids?
Provitamin A carotenoids such as beta-carotene are generally considered safe because they are not associated with specific adverse health effects. Their conversion to vitamin A decreases when body stores are full. A high intake of provitamin A carotenoids can turn the skin yellow, but this is not considered dangerous to health.
Beta-carotene and cancer
It has been shown in trials that the use of synthetically-produced beta carotene (that is, beta carotene in supplement form such as the pills typically sold in stores) increases the rate of lung cancer and prostate cancer, and increases mortality in smokers. These results have been observed in beta carotene supplements synthetically made and not in foods with naturally occurring beta carotene. On the contrary carotenoid-rich fruits and vegetables are known to lower lung cancer rates.
Vitamin A and osteoporosis
One small study of nine healthy individuals in Sweden found that the amount of vitamin A in one serving of liver may impair the ability of vitamin D to promote calcium absorption.
It was found that a dietary retinol(animal source of vitamin A) intake greater than 1,500 mcg/day (more than twice the recommended intake for women) was associated with reduced bone mineral density and increased risk of hip fracture as compared to women who consumed less than 500 mcg/day
There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables, and increased risk of osteoporosis. Current evidence points to a possible association with vitamin A as retinol only.