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Vitamin A Facts
Vitamin A is one of the fat-soluble vitamins. It is found in foods that contain fat, and is absorbed and transported with other dietary fats. This means the vitamin can be stored in your body, which brings to light two significant facts: One, you can go a few days without eating any vitamin A since you'll have some stores; and two, there is a potential to get an overdose-even a toxicity-if you eat too much of it, because it will remain in your body.
How would a person get too much vitamin A? The occasions are fairly rare, and pretty limited to either overdosing on a lot of supplements, or eating too much polar bear liver-an excellent source of this vitamin. Excessive amounts of chicken liver, beef liver, or fish liver can be harmful as well, but this would mean for most people eating several ounces a day, every day, for many weeks in a row. Feel free to enjoy an occasional meal of chicken or beef liver (once a week), by all means, and don't worry about overdosing! Other sources of vitamin A include egg yolks and fortified milk.
Why, then, are carrots named as such a great source of vitamin A if they are a vegetable? There is a compound in carrots, and in many brightly colored fruits and vegetables, called beta carotene. This compound can be converted to vitamin A in your body. Even though the actual vitamin is found only in animal sources, a vegetarian could get all they need from the beta carotene in a good variety of green and orange vegetables, mangoes, peaches, and sweet potatoes.
Can you overdose on beta carotene and have toxic symptoms like people who overdose on vitamin A? The answer is no. Your body will only continue to convert beta carotene to vitamin A for as long as you are in need. You can take in too much beta carotene, and people have done this while on juice fasts or carrot binges. It takes an awful lot to get to the point of 'too much' and then the main symptom is that your skin will turn orange. This is much more common in infants (because of their tiny body mass) who may develop a taste for orange or dark green vegetables (pumpkin, squash, carrots, spinach) and have their overjoyed mothers continue to feed them all they want. Just stop when the baby turns orange and the condition will reverse itself soon.
What does vitamin A do for your vision? It can't improve your distance vision or help you see more clearly, but a deficiency can certainly harm your vision in several ways. One form of vitamin A in your body, retinal, helps nerves transmit the image of what you see to your brain. When you are in a dark situation (such as driving at night) and light flashes (such as oncoming headlights), certain compounds in the visual cycle are bleached out and need to be refreshed by having a good supply of retinal available. If a person is deficient in vitamin A it takes much longer for their eyes to adjust to be able to see again.
Another way vitamin A helps your vision is by maintaining the moisture of your mucous membranes. In some underdeveloped countries, vitamin A deficiency is rampant (not enough fruits, vegetables, or meat around, and certainly no fortified milk available). These people suffer from a hardening and drying of their mucous membranes, including their eyes, the lining of their nose, lungs, stomach and intestines. The eyes can become so hardened that blindness results. The healthy linings of the lungs are no longer able to fight infections. The damage to the digestive tract causes digestive problems. These people can die of a vitamin A deficiency, but most likely they are suffering from multiple deficiencies because they do not have access to healthy foods.
Fortunately we rarely see serious vitamin A deficiencies in this country. Be sure to get a good source of beta carotene or vitamin A at least every other day, either from meat or dairy products, or from colorful fruits and vegetables; and help your eyes and your immune system keep you well!
Laurie Beebe is a registered dietitian certified in adult weight management. Please visit Laurie's website, "Shaping Your Future" at http://www.mycoachlaurie.com for diet tips, links to great books and websites, or to sign up for a free monthly newsletter!
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