Understanding Vitamin A


People use to get a dose of vitamin A from cod liver oil but it tastes awful and often cause digestive upsets. Once known as the ‘anti-infective vitamin”, vitamin A has recognition as a major player in immune status. Carotenes, some of which can be converted into vitamin A, are immune enhancers. Carotenes represent the most widespread group of naturally occurring pigments in nature. They are an intensely colored group of fat-soluble compounds. These compounds not only play a vital role in protecting the organism or plant against the tremendous amount of free radicals produced during photosynthesis. Vitamin A is termed retinol, signifying that it is an alcohol involved in the function of the retina of the eye.

The Role It Plays

Vitamin A is important for a wide range of body functions. We need vitamin A for healthy eyes, cell growth, and a strong immune system.

Vitamin A helps fend off infections and illnesses by helping your body’s epithelial tissues (thin layer of cells found in skin, mouth, eyes, arteries, throat lungs, digestive tissues, urinary tract, etc) grow and repair themselves. Without vitamin A these cells become stiff, dry and unable to keep offenders out. When this happens germs are allowed a passage into our body. Even when we do have enough vitamin A sometimes these offenders make it in to our body and then vitamin A helps our immune system get them out. Vitamin A has been shown to help children get over the measles faster and with fewer complications. It also helps babies with respiratory infections. If we’re low on vitamin A we’re more susceptible to illness, especially viral infections.

Vitamin A is essential for healthy eyes. Vitamin A helps you see well in the dark. Our retina contains large amounts of vitamin A, especially in the rods that are used for night vision. A diet rich in carotenoids, especially beta carotene, helps prevent cataracts by mopping up free radicals before they can damage the lens of the eye. Vitamin A helps prevent age-related macular degeneration (AMD). Children and teens need plenty of vitamin A to help grow properly and build strong bones and teeth. Adults need vitamin A to replace old, worn-out cells with new replacement cells and to keep bones and teeth healthy. The cells of our skin grow very rapidly (our outer skin turns over completely in just about four weeks). All rapidly growing cells need plenty of vitamin A. Taking vitamin A has been proven to cut your chances of getting basal cell carcinoma , the most common skin cancer, dramatically. Beta carotene foods play a major role in preventing cancer, especially cancer of the lung, stomach, and cervix. However, beta carotene supplements may have a bad effect on people who are already at high risk for lung cancer (people who smoke cigarettes and drink alcohol).

Beta carotene supplements alone can’t overcome a lifetime of smoking, drinking, and eating a diet low in valuable nutrients found in fruits and vegetables. You need to eat foods that are high in all the carotenoids, not just beta carotene, to help ward off cancer. Researchers have only focused on beta carotene because it’s easy to measure in our blood. People who eat foods high in beta carotene have fewer heart attacks and strokes. But here the results are the same as with cancer, you need to eat all the carotenoids, not just beta carotene.

Types of Vitamin A

It used to be believed that the only way to get vitamin A was by eating animal foods such as eggs or liver that naturally contain retinoids. Your body uses this type of vitamin A as soon as you eat it. The other way to get vitamin A is by eating plant foods that contain carotenes – the orange, red, and yellow substances that give plant foods their colors. There are two main carotenes: alpha carotene (a-carotene) and beta carotene (B-carotene). There are over 600 carotenoids, of which only 30 to 50 have vitamin A activity. Researchers have described beta carotene as the most active of the carotenoids because of its higher provitamin A activity, but several other carotenes have greater antioxidant effects. The most abundant of the carotenes is beta carotene. Our bodies easily converts beta carotene into vitamin A in the small intestine, where special enzymes split one molecule of beta carotene in half to make two molecules of vitamin A. The best part, is that if you don’t need vitamin A right then, most of it circulates in your blood and enters into our cells; the rest of it gets stored in our fatty tissues. When we do need vitamin A, our liver quickly converts the stored beta carotene. There are plenty of reasons why it’s better to convert your vitamin A from carotenes rather than getting them straight form animal foods or supplements. Almost half of the carotenes you eat are converted to vitamin A in our liver and small intestine as we need it. The rest act as powerful antioxidants. Beta carotene is especially good at quenching oxidation and alpha carotenes is an even better antioxidant (almost 10 times better). Large doses of vitamin A can be toxic and at low doses overdose symptoms can occur. Since our body converts carotenes to vitamin A it’s almost impossible to overdose. Beta carotene is non-toxic so even if we are storing too much in our fatty tissues the only thing that’d happen would be our skin turning yellowish.


There are two ways vitamin A is measured: International Units (IU) and Retinol Equivalents (RE). IU doesn’t take into account for the difference in absorption from vitamin A and beta carotene so to give a more accurate idea of how much vitamin A is in a food or supplement the RE measurement has come about. To complicate things, vitamin manufacturers still list vitamin A and beta carotene on the label in IU’s. To figure out what is in your supplement divide by 5 (4,000 IU is equal to 800 RE). Vitamin A can be toxic in large amounts, no one should exceed the RDA.

0-1 years; 375 RE or 1,875 IU

1-3 years; 400 RE or 2,000 IU

4-6 years; 500 RE or 2,500 IU

7-10 years; 700 RE or 3,500 IU

Men 11+ years; 1,000 RE or 5,000 IU

Women 11+ years; 800 RE or 4,000 IU

Pregnant women; 800 RE or 4,000 IU

Nursing women; 1,300 RE or 6,500 IU

Safe Dosage

Beta carotene is safe even in very large doses. There is not an RDA for beta carotene. However, it is suggested that we get a daily dose of 6 mg. This is a low suggestion. Other’s suggest getting 30 mg a day. This is a high suggestion. Somewhere in the middle is better – about 15 mg a day (that would be the equivalent of 25,000 IU or 5,000 RE) of vitamin A, but without the toxic side effects. Most people on the SAD get maybe 1.5 mg of beta carotene daily.

Supplement Forms

Vitamin A supplements usually come in soft gel caps in retinol or retinyl palmitate form – either is fine, but retinyl palmitate is best for people with intestinal problems. Getting more than 5,000 IU or 1,000 RE a day can be harmful. To avoid possible problems, take mixed carotenes instead, you’ll get the vitamin A you need along with extra antioxidant protection. Beta carotene supplements come in two forms: water-based and oil-based. Water-based carotenes are absorbed better than oil-based. Oil-based supplements come in gelcaps and water-based supplements come in solid form. Whichever you choose, oil-based or water-based supplements, look for a product that is bright orange-red in color and store it away from light. Water-based supplements are made either from a type of algae called Dunaliella or from palm oil. Of these, palm oil carotenes are the best form because it contains mixed carotenoids. The best way to get all the carotenoids is to eat plenty of fruits and vegetables. If you want to take a supplement, take mixed carotenoids.

Make It Work Better

To get the most out of vitamin A and beta carotene, be sure to also get vitamin E, zinc, and selenium. Vitamin E helps vitamin A work more effectively. Extra vitamin E is needed if you take large doses (more than 15 g a day) of beta carotene supplements. You need zinc to transport vitamin A around your body and you need selenium to help beta carotene work more effectively.

Good Sources

A good rule of thumb is to eat foods that are red, orange, and yellow. Carotenes are found in practically all fruits and vegetables including dark green leafy vegetables, you just can’t see the bright red colors because they’re disguised by the green.

Beta carotene is found in dark green leafy vegetable, carrots, sweet potatoes, squash, spinach, apricots, and green peppers.

Alpha carotene is found in dark green leafy vegetables, carrots, squash, corn, watermelon, green pepper, potatoes, apples, and peaches.

Gamma carotene is found in carrots, sweet potatoes, corn, tomatoes, watermelons, apricots.

Beta zeacarotene is found in corn, tomatoes, yeast and cherries.

Cryptoxanthin is found in corn, green peppers, persimmons, papayas, lemons, oranges, apples, apricots, paprika, and poultry.

Beta apo 8′ carotenal is found in citrus fruits and green leafy vegetables.

Beta apo 12′ carotenal is found in alfalfa meal.

Lycopne is found in tomatoes, carrots, green peppers, apricots, and pink grapefruit.

Zeaxanthin is found in spinach, paprika, corn and fruits.

Lutein is found in dark green leafy plants, corn, potatoes, spinach, carrots, tomatoes, and fruits.

Canthaxanthin is found in mushrooms, trout, and crustaceans.

Capsanthin is found in red peppers and paprika.

The best sources are fresh apricots, cooked asparagus, beet greens, cooked broccoli, cantaloupe, carrot, cooked collard greens, cooked kale, orange, peach, sweet red pepper, stewed prunes, cooked spinach, winter squash, butternut squash, sweet potato, tomato, cooked turnip greens, yam and watermelon.


A variety of factors influence the absorption of vitamin A and carotenes. Unlike retinol, carotenes require bile acids to facilitate absorption. Other factors that affect vitamin A and carotene absorption include: the presence of fat, protein, and antioxidants in the food; the presence of bile and normal pancreatic enzymes; and the integrity of mucosal cells.


If you don’t get enough vitamin A, you will develop night blindness. An early sign of vitamin A deficiency is skin that is rough, dry, and scaly. After several weeks without much vitamin A in your diet, you’d start to have some signs of deficiency, a condition called follicular hyperkeratosis. When this happens, your epithelial tissues, especially on your skin, start to make too much of a hard protein called keratin. You start to get little deposits of keratin that look like goose bumps around hair follicles and make your skin feel rough and dry. Vitamin A deficiency can also cause reproductive problems for both men and women. A shortage will make you more likely to get respiratory infections, sore throats, sinus infections, and ear infections. If you have liver disease, cystic fibrosis, or chronic diarrhea, these problems reduce the amount of vitamin A you absorb or store. If you abuse alcohol, it will reduce the amount of vitamin A and beta carotene stored in your liver. If you have beta carotene combined with alcohol it could do a lot of damage to your liver. People who smoke cigarettes have low beta carotene levels. Birth control pills raise the amount of vitamin A in your blood but reduces the amount stored in your liver (this doesn’t happen with beta carotene). People who are sick or have a chronic infection have lower vitamin A levels. If you’re under a great deal of physical or psychological stress have lower vitamin A levels. If you take bile-sequestering drugs (Cholybar, Colestid, or Questran) to lower your cholesterol, they can keep you from absorbing fat-soluble vitamins like vitamin A correctly. If you take these drugs, hopefully your doctor has already told you to take a vitamin A supplement, you should also know you should take the supplements at a different time than the drugs. If you take the drug methotrexate (Folex, Methotrate, Mexate, Rheumatrex) to treat arthritis, psoriasis, or cancer, it affects your intestines, making it harder to absorb vitamin A and beta carotene.


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