what is vitamin A? Why is it good for us?

Answer 1

vision, growth, and development; the development and maintenance of healthy skin, hair, and mucous membranes; immune functions; and reproduction.

Answer 2

What is Vitamin A?
Vitamin A (retinol) is only found in in certain animal tissues. Retinol can be toxic in large doses. However, carotenoids (found in fruits and vegetables) are converted in the body into vitamin A. Unlike retinol, carotenoids can be consumed without fear of toxicity. The most widespread and most active form of carotenoid is beta-carotene.

Function
Essential for good eyesight
Enables tissue growth and bone development
Necessary for healthy mucous membranes to protect against infection
Essential for reproductive system

Signs of deficiency
Dry, scaly skin
Poor vision (especially at night times)
Predisposition to infections (particularly lungs, ailmentary canal and urinary tract)

Answer 3

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.) [1-5]. 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 [1,6-10]. 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 [8]. 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 [9-11].

In general, there are two categories of vitamin A, depending on whether the food source is an animal or a plant.

Vitamin A found in foods that come from animals is called preformed vitamin A. It is absorbed in the form of retinol, one of the most usable (active) forms of vitamin A. Sources include liver, whole milk, and some fortified food products. Retinol can be made into retinal and retinoic acid (other active forms of vitamin A) in the body [1].

Vitamin A that is found in colorful fruits and vegetables is called provitamin A carotenoid. They can be made into retinol in the body. In the United States, approximately 26% of vitamin A consumed by men and 34% of vitamin A consumed by women is in the form of provitamin A carotenoids [1]. Common provitamin A carotenoids found in foods that come from plants are beta-carotene, alpha-carotene, and beta-cryptoxanthin [11]. Among these, beta-carotene is most efficiently made into retinol [1,13-15]. Alpha-carotene and beta-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene [1].

Of the 563 identified carotenoids, fewer than 10% can be made into vitamin A in the body [12]. Lycopene, lutein, and zeaxanthin are carotenoids that do not have vitamin A activity but have other health promoting properties [1]. The Institute of Medicine (IOM) encourages consumption of all carotenoid-rich fruits and vegetables for their health-promoting benefits.

Some provitamin A carotenoids have been shown to function as antioxidants in laboratory studies; however, this role has not been consistently demonstrated in humans [1]. Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases [3,14-15].

Table 1: Selected animal sources of vitamin A [18]Food Vitamin A (IU)* %DV**
Liver, beef, cooked, 3 ounces 27,185 545
Liver, chicken, cooked, 3 ounces 12,325 245
Milk, fortified skim, 1 cup 500 10
Cheese, cheddar, 1 ounce 284 6
Milk, whole (3.25% fat), 1 cup 249 5
Egg substitute, ¼ cup 226 5
Carrot juice, canned, ½ cup 22,567 450
Carrots, boiled, ½ cup slices 13,418 270
Spinach, frozen, boiled, ½ cup 11,458 230
Kale, frozen, boiled, ½ cup 9,558 190
Carrots, 1 raw (7½ inches) 8,666 175
Vegetable soup, canned, chunky, ready-to-serve, 1 cup 5,820 115
Cantaloupe, 1 cup cubes 5,411 110
Spinach, raw, 1 cup 2,813 55
Apricots with skin, juice pack, ½ cup 2,063 40
Apricot nectar, canned, ½ cup 1,651 35
Papaya, 1 cup cubes 1,532 30
Mango, 1 cup sliced 1,262 25
Oatmeal, instant, fortified, plain, prepared with water, 1 cup 1,252 25
Peas, frozen, boiled, ½ cup 1,050 20
Tomato juice, canned, 6 ounces 819 15
Peaches, canned, juice pack, ½ cup halves or slices 473 10
Peach, 1 medium 319 6
Pepper, sweet, red, raw, 1 ring (3 inches diameter by ¼ inch thick) 313 6

Answer 4

Keeps skin and tissue healthy
Maintains vision and eye health
Supports red cell health
Role in immune system function
Promotes wound healing
Resists infection
Develops bones
Forms sperm
Promotes healthy fetal development
Improves acne and psoriasis
May reduce infant mortality from measles
With antibiotics, may speed recovery from peritonitis
May improve survival from chronic myelogenous leukemia
May reduce symptoms of osteoarthritis

Answer 5

Is a group of compounds that play an important role in vision, and bone growth, reproduction. Also helps the immune system.

Answer 6

karotin