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General Nutrition and Diet Facts

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Vitamin A and carotenoids

 

What is 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.
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.
Vitamin A that is found in colorful fruits and vegetables is called provitamin A carotenoid. They can be made into retinol in the body. Common provitamin A carotenoids found in foods that come from plants are beta-carotene, alpha-carotene, and beta-cryptoxanthin. Among these, beta-carotene is most efficiently made into retinol. Alpha-carotene and beta-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene.
Of the 563 identified carotenoids, fewer than 10% can be made into vitamin A in the body. Lycopene, lutein, and zeaxanthin are carotenoids that do not have vitamin A activity but have other health promoting properties.

Foods that provide vitamin A

Retinol is found in foods that come from animals such as whole eggs, milk, and liver. Most fat-free milk are fortified with vitamin A to replace the amount lost when the fat is removed. Fortified foods such as fortified breakfast cereals also provide vitamin A. Provitamin A carotenoids are abundant in darkly colored fruits and vegetables. It has been indicated that major dietary contributors of retinol are milk, margarine, eggs, beef liver and fortified breakfast cereals, whereas major contributors of provitamin A carotenoids are carrots, cantaloupes, sweet potatoes, and spinach.
Vitamin A in foods that come from animals is well absorbed and used efficiently by the body. Vitamin A in foods that come from plants is not as well absorbed as animal sources of vitamin A.

Selected animal sources of vitamin A

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


Selected plant sources of vitamin A (from beta-carotene)

Food Vitamin A (IU)* %DV**
  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


* IU = International Units
** DV = Daily Value.

DVs are reference numbers based on the Recommended Dietary Allowances (RDAs). They were developed to help consumers determine if a food contains a lot or a little of a nutrient.

Recommended intakes of vitamin A

Age (years) Children (mcg RAE) Males (mcg RAE) Females(mcg RAE) Pregnancy (mcg RAE) Lactation (mcg RAE)
  1-3   300 (1,000 IU)            
  4-8   400 (1,320 IU)            
  9-13   600 (2,000 IU)            
  14-18      900 (3,000 IU)   700 (2,310 IU)   750 (2,500 IU)   1,200(4,000 IU)
  19+      900 (3,000 IU)   700 (2,310 IU)   770(2,565 IU)   1,300 (4,300 IU)


Adequate Intakes (AIs) for vitamin A for infants

Age (months) Males and females (mcg RAE)
  0-6   400 (1,320 IU)
  7-12   500 (1,650 IU)


When can vitamin A deficiency occur?

Vitamin A deficiency is common.Vitamin A deficiency is most often associated with strict dietary restrictions and excess alcohol intake. Severe zinc deficiency, which is also associated with strict dietary limitations, often accompanies vitamin A deficiency. Zinc is required to make retinol binding protein (RBP) which transports vitamin A. Therefore, a deficiency in zinc limits the body's ability to move vitamin A stores from the liver to body tissues.
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 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.
There is increased interest in early forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause obvious deficiency symptoms. This mild degree of vitamin A deficiency may increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Children who are considered to be at increased risk for subclinical vitamin A deficiency include:
  • toddlers and preschool age children;
  • children living at or below the poverty level;
  • children with inadequate health care or immunizations;
  • children living in areas with known nutritional deficiencies;
  • recent immigrants or refugees from developing countries with high incidence of vitamin A deficiency or measles; and
  • children with diseases of the pancreas, liver, or intestines, or with inadequate fat digestion or absorption.
A deficiency can occur when vitamin A is lost through chronic diarrhea and through an overall inadequate intake, as is often seen with protein-energy malnutrition. Low blood retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories, and zinc, since these nutrients are needed to make RBP. Iron deficiency can also affect vitamin A metabolism, and iron supplements provided to iron-deficient individuals may improve body stores of vitamin A and iron.
Excess alcohol intake depletes vitamin A stores. Also, diets high in alcohol often do not provide recommended amounts of vitamin A. It is very important for people who consume excessive amounts of alcohol to include good sources of vitamin A in their diets. Vitamin A supplements may not be recommended for individuals who abuse alcohol, however, because their livers may be more susceptible to potential toxicity from high doses of vitamin A.

Who may need extra vitamin A to prevent a deficiency?

It is recommended vitamin A supplements for two subgroups of children likely to be at high risk for subclinical vitamin A deficiency: children aged 6 months to 24 months who are hospitalized with measles, and hospitalized children older than 6 months.
Fat malabsorption can result in diarrhea and prevent normal absorption of vitamin A. Over time this may result in vitamin A deficiency. Those conditions include:

Celiac disease:
Often referred to as sprue, celiac disease is a genetic disorder. People with celiac disease become sick when they eat a protein called gluten found in wheat and some other grains. In celiac disease, gluten can trigger damage to the small intestine, where most nutrient absorption occurs. Approximately 30% to 60% of people with celiac disease have gastrointestinal-motility disorders such as diarrhea.They must follow a gluten-free diet to avoid malabsorption and other symptoms.
Crohn's disease:
This inflammatory bowel disease affects the small intestine. People with Crohn's disease often experience diarrhea, fat malabsorption, and malnutrition.
Pancreatic disorders:
Because the pancreas secretes enzymes that are important for fat absorption, pancreatic disorders often result in fat malabsorption . Without these enzymes, it is difficult to absorb fat. Many people with pancreatic disease take pancreatic enzymes in pill form to prevent fat malabsorption and diarrhea.
Healthy adults usually have a reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of temporary or short-term fat malabsorption. Long-term problems absorbing fat, however, may result in deficiency. In these instances physicians may recommend additional vitamin A.
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.

Health risks of too much vitamin A?

Hypervitaminosis A refers to high storage levels of vitamin A in the body that can lead to toxic symptoms. There are four major adverse effects of hypervitaminosis A: birth defects, liver abnormalities, reduced bone mineral density that may result in osteoporosis, and central nervous system disorders.
Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time. Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and muscular uncoordination. Although hypervitaminosis A can occur when large amounts of liver are regularly consumed, most cases result from taking excess amounts of the nutrient in supplements.

Tolerable Upper Intake Levels (ULs) for retinol

Age (years) Children (mcg) Males (mcg) Females(mcg) Pregnancy (mcg) Lactation (mcg)
  0-1   600 (2,000 IU)            
  1-3   600 (2,000 IU)            
  4-8   900(3,000 IU)            
  9-13   1,700 (5610 IU)      )      
  14-18      2,800 (9,240 IU)   2,800 (9,240 IU)   2,800 (9,240 IU)   2,800 (9,240 IU)
  19+   3,000 (10,000 IU)   3,000 (10,000 IU)   3,000 (10,000 IU)   3,000 (10,000 IU)   3,000 (10,000 IU)


Retinoids are compounds that are chemically similar to vitamin A. Over the past 15 years, synthetic retinoids have been prescribed for acne, psoriasis, and other skin disorders. Isotretinoin (Roaccutane® or Accutane®) is considered an effective anti-acne therapy. At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne. The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.

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.
Clinical trials that associated beta-carotene supplements with a greater incidence of lung cancer and death in current smokers raise concerns about the effects of beta-carotene supplements on long-term health; however, conflicting studies make it difficult to interpret the health risk. Beta-carotene supplements are not advisable for the general population. However, they may be appropriate as a provitamin A source for the prevention of vitamin A deficiency in specific populations.
Nutrient needs should be met primarily through consuming foods. Foods provide an array of nutrients and other compounds that may have beneficial effects on health. In certain cases, fortified foods and dietary supplements may be useful sources of one or more nutrients that otherwise might be consumed in less than recommended amounts. However, dietary supplements, while recommended in some cases, cannot replace a healthful diet.

 


 
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