All About Vitamin A

Vitamin A – How Much Do You Need?

Vitamin A is a fat soluble vitamin. If you’re like most Americans, you get an adequate amount in your diet. Like other fat soluble vitamins, the majority of your body’s vitamin A is stored in the liver and released into the bloodstream as needed. Once you establish your fat soluble vitamin stores, you can go up to months at a time without consuming more.

The RDA for Vitamin A:

  • for males 14 and older – 900 micrograms RAE
  • for females 14 and older – 700 micrograms RAE
  • for pregnant women – 770 micrograms RAE
  • for lactating women – 1,300 micrograms RAE

Why is Vitamin A Important?

Vitamin A is crucial for vision, for maintaining healthy cells (especially skin cells), for fighting infections and strengthening the immune system, and for promoting growth and development, including maintenance of healthy bones.

Sources of Vitamin A

Dietary vitamin A can come from both animal and plant foods.

Vitamin A in animal products

Vitamin A comes from animal food sources in the form of retinoids. These foods include:

  • Liver and fish liver oils (i.e., cod liver oil)
  • Milk fat (as in whole milk, butter, egg yolks and other dairy products)
  • Foods fortified with vitamin A: margarine, some breakfast cereals, reduced fat milk

Your body absorbs about 75% of retinoids consumed in the diet.

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Vitamin A intake comes from fruits and vegetables in the form of carotenoids. The best sources of carotenoids are dark green, yellow-orange and red fruits and vegetables.  The body converts the colorful pigments into Vitamin A once eaten. Carotenoids are called provitamins because they don’t actually become active vitamins until your body absorbs them.

Beta-carotene (the yellow-orange pigment) produces the most vitamin A of any of the carotenoids, about one-third of your total vitamin A. The body absorbs provitamins less efficiently than the retinoids found in animal products.

Some good sources of carotenoids:

  • Sweet potato – baked in the skin
  • Carrots, cooked
  • Collards, cooked
  • Spinach, cooked
  • Pumpkin, cooked
  • Cantaloupe
  • Melon
  • Tomatoes
  • There are numerous others, just think yellow, orange, red and deep green

A few minutes of cooking breaks down some of the chemical bonds in food. This helps release carotenoids and makes them easier to absorb in your system. For example, you will absorb about 2 times more nutrients from a cup of slightly cooked spinach versus 3 cups of raw spinach. Be careful not to cook it too long, however, because the longer you cook it, the more vitamins you lose.

Other Cool Facts About Carotenoids

  • They are antioxidants
  • They boost your immune system
  • They can reduce risk of age-related degeneration of the eye and risk of cataracts
  • They can reduce the risk of cancer and heart disease
  • Dietary fat, protein and vitamin E enhance carotenoid absorption, but dietary fiber reduces its absorption

So be sure to eat your yellow, orange, red and deep green fruits and vegetables!

Vitamin A Deficiency

Dietary vitamin A deficiency is rare in North America and western Europe, but is the leading cause of childhood blindness worldwide. Also, vitamin A deficiency has been shown to slow growth and development and leads to bone deformities.

In the United States, those at risk for vitamin A deficiency include:

  • Newborns (due to lack of vitamin A stores in their liver)
  • Those with alcoholism or liver disease
  • Those who suffer from fat-malabsorption syndromes
  • Those who suffer from anorexia nervosa
  •  Those with an inadequate intake of zinc (which is required for the body to use Vitamin A efficiently)

There are various symptoms of vitamin A deficiency, but if caught quickly they can be reversed.

  • Vision: Night blindness (the inability of the eyes to adjust to dim light or to regain vision quickly after exposure to a flash of bright light) is an early symptom. If the deficiency worsens color blindness and then permanent blindness can result.
  • SkinYour skin cells are the first line of defense protecting your body and they are destroyed and replaced rather quickly. Vitamin A is needed for this rapid cell turnover. Signs of vitamin A deficiency show up early in the skin.
  • Other CellsVitamin A deficiency can disrupt the cells ability to produce mucous.  This particularly affects the mouth, respiratory tract, urinary tract and male and female reproductive processes.  Also, if the affected cells are located near sensory receptors, you can lose your sense of smell and taste.
  • Immune Function: Vitamin A deficiency leaves a person highly susceptible to bacterial, parasitic and viral infections. People with severe vitamin A deficiencies have such impaired immune systems that simple infections can be hazardous.

Too Much Vitamin A is Toxic

It’s highly unlikely that you will overdose on vitamin A through your diet alone. A healthy diet is rich in a variety of foods and by eating many different things you will help keep all of your vitamin levels in check.

The potential for overdose increases, however, as more and more people are taking megadoses of nutritional supplements. (I’m not talking about everyday multiple vitamins, but extreme doses of Vitamin A in supplemental form). Ninety percent of the body’s vitamin A supply is stored in the form of a retinoid in the liver. (The remainder is stored in fat tissue, the lungs and kidneys).  A healthy liver can store up to a year’s supply of vitamin A, but taking large doses of vitamin A supplements can exceed this capacity and lead to toxicity.

Overindulging in vitamin A supplements is dangerous.

Toxicity Symptoms

There are a wide range of symptoms which can be short term or long term, including fatigue, vomiting, abdominal pain, bone and joint pain, loss of appetite, skin disorders, headache, blurred or double vision, eye damage, swelling of the brain, psychiatric changes, osteoporosis, hip fracture, liver damage, coma, and so many more.

Vitamin A and Pregnancy

Birth defects can occur if vitamin A is taken in excess during pregnancy, especially if taken two weeks prior to conception and during the two months following. Pregnant women should take prenatal supplements containing beta-carotene as the vitamin A source and avoid retinol. Even retinoids taken for acne (both topical and oral) should be avoided at this time.  Because even the topical Retin-A absorbs through the skin and accumulates in fat stores, this type of treatment should be discontinued long before pregnancy.

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Source:

Insel,P., Ross,D., McMahon,K., Bernstein,M., Nutrition Fourth Edition. Burlington: Jones & Bartlett, 2013

 

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One thought on “All About Vitamin A

  1. Wayne Pinnell

    Thanks – I feel like I got all my vitamins today!! Of course – they may just have been in print form.

    Reply

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