Vitamin A

Vitamin A was the first vitamin to be discovered, back in 1913. Twenty-four centuries ago in ancient Greece, the importance of Vitamin A was already well known. Back then, Hippocrates, the father of modern medicine, told patients with failing eyesight to eat beef liver. When they did, they were able to see much better, especially at night. Hippocrates didn't know why liver helped so much, but today we know that animal liver is a rich source of Vitamin A—and we know that our eyes need plenty of Vitamin A to work properly in the dark.

Today we know a lot more than Hippocrates about the importance of Vitamin A for a wide range of body functions—from keeping your skin smooth to warding off cancer. We also know that Vitamin A is only half the story. Health researchers are very excited about carotenes, the natural plant forms of Vitamin A. Your body converts some of the carotenes in plant foods into the Vitamin A you need and uses the leftovers to help you fight off the free radicals that can cause cancer, heart disease, and other problems.

Why You Need Vitamin A
When Vitamin A was first discovered, it was called the “anti-infective agent.” Lab animals fed a diet low in animal foods, vegetables, and fruits soon got eye infections—infections that cleared up as soon as these foods were put back into their diet. The mysterious “agent” in the foods turned out to be a fat-soluble substance that was dubbed Vitamin A.

To fend off infections and illnesses, Vitamin A helps you put up strong front-line barriers to infection. How? By helping your body's epithelial tissues—the cells that make up your skin and line your eyes, mouth, nose, throat, lungs, digestive tract, and urinary tract—grow and repair themselves.

These tissues line your body's external and internal surfaces and keep out trespassers. Without enough Vitamin A, these cells become stiff, dry, and much more likely to let their guard down. When that happens, germs can easily pass through them and into your body.

Even if your body has plenty of Vitamin A, those nasty germs still sometimes get through your outer defenses. When that happens, Vitamin A helps your immune system come riding to the rescue.

Children and teens need plenty of Vitamin A to help them grow properly and build strong bones and teeth. Your need for Vitamin A doesn't stop then, though. Even after you're full grown, your body constantly replaces old, worn-out cells with new ones. You need Vitamin A to produce healthy replacement cells and to keep your bones and teeth strong.

Why You Need Carotenes Even More
After Vitamin A was first discovered, researchers believed that the only way to get your A's was by eating animal foods such as eggs or liver that naturally contain retinoids, or preformed Vitamin A. Your body can use this Vitamin A as is just as soon as you eat it.

In 1928, researchers discovered the other way to get your A's: by eating plant foods that contain carotenes—the orange, red, and yellow substances that give plant foods their colors. The most abundant of the carotenes in plant foods is beta carotene. Your body easily converts beta carotene to Vitamin A in your small intestine, where special enzymes split one molecule of beta carotene in half to make two molecules of Vitamin A.

If you don't happen to need any Vitamin A just then, you don't convert the beta carotene. Instead, a lot of it circulates in your blood and enters into your cells; the rest gets stored in your fatty tissues. Whenever you need some extra A's, your liver quickly converts the stored beta carotene.

Carotenes are just one small group of plant substances in the much larger carotenoid family. Two main carotenes that are converted to Vitamin A: alpha carotene and beta carotene. Why is it better to convert your A's from the carotenes in plant foods rather than getting them straight from animal foods or supplements? There are some very good reasons:
• The antioxidant power of carotenes. About 40 percent of the carotenes you eat are converted to Vitamin A in your liver and small intestine as you need it. The rest act as powerful antioxidants. Beta carotene is especially good at quenching singlet oxygen. Alpha carotene is an even better antioxidant—it may be ten times as effective for mopping up free radicals.
• The safety of carotenes. Large doses of supplemental Vitamin A can be toxic—and some people show overdose symptoms even at lower doses. Your body converts carotenes to Vitamin A only as needed, however, so it's almost impossible to overdose. Also, beta carotene is nontoxic—even if you store so much in your fatty tissues that you turn yellow, it's harmless.
• The health benefits of fruits and vegetables. Carotenes are found in almost every fruit and vegetable. Five servings a day will give you all the Vitamin A you need, along with plenty of other vitamins, minerals, antioxidants, and fiber. What you won't get are calories and the cholesterol found in animal sources of preformed Vitamin A such as beef liver.

The RDA for Vitamin A
If you eat a typical diet, you'll get some of your Vitamin A the preformed way  from milk, eggs, and meat. You'll get the rest in the form of carotenes (mostly beta) from the fruits and vegetables you eat. That means the RDA for Vitamin A assumes that you get some of your A's from animal foods  and some from plant foods. 

Vitamin A is an essential nutrient, so it's got an established RDA. Beta carotene, although it's certainly important, isn't considered essential, so it doesn't have an RDA. The U.S. Department of Agriculture and the National Cancer Institute suggest a daily dose of 6 mg, but many nutritionists feel this is too low. Some think you should take as much as 30 mg a day. A good compromise might be 15 mg a day—roughly the equivalent of 25,000 IU (5,000 RE) of Vitamin A. That's about five times the RDA for Vitamin A, but without the toxic side effects. 
Studies show that most people get the RDA for Vitamin A every day, but only a few get anywhere near the suggested 6 mg of beta carotene. Most people eat only about 1.5 mg of beta carotene daily. On an average day, only about 20 percent of the population eats any fruits and vegetables rich in beta carotene.

Vitamin A Cautions
Taking supplements that contain the RDA for Vitamin A is generally safe for everyone, but use caution. Vitamin A in large doses can be toxic, causing a condition called hypervitaminosis A. Symptoms of A overload include blurred vision, bone pain, headaches, diarrhea, loss of appetite, skin scaling and peeling, and muscular weakness. Vitamin A toxicity doesn't usually occur until 
you've been taking really large doses (more than 25,000 IU daily) for a long time, but don't take any chances—stick to the RDA. Fortunately, most symptoms of Vitamin A toxicity gradually go away without lasting damage when you stop taking it.
Be very careful about Vitamin A supplements if you are or might become pregnant. Too much Vitamin A (over 5,000 IU or 1,000 RE) can cause birth defects, especially if taken in the first seven weeks of pregnancy—when you might not even realize you're pregnant. Today many doctors suggest that women of childbearing age take beta carotene instead of Vitamin A supplements. 

Are You Deficient?
Generally speaking, a real Vitamin A deficiency is rare in the Western world, because so many common foods, including milk and breakfast cereals, are fortified with it.
Almost everyone gets the RDA or pretty close to it, but some people are at high risk of a Vitamin A deficiency. If you fall into any of these categories, you may need more Vitamin A than you're actually getting:
• You have liver disease, cystic fibrosis, or chronic diarrhea. These problems can reduce the amount of Vitamin A you absorb or store.
• You abuse alcohol. Alcohol reduces the Vitamin A and beta carotene stored in your liver. On the other hand, animal studies suggest that beta carotene combined with alcohol is a one-two punch that could do a lot of damage to your liver.
• You smoke. People who smoke cigarettes have low beta carotene levels.
• You take birth control pills. The Pill raises the amount of Vitamin A in your blood but reduces the amount you store in your liver. (This doesn't happen with beta carotene.)
• You're sick or have a chronic infection. Being sick makes you produce extra free radicals, which lowers your Vitamin A level.
• You're under a great deal of stress—physical or psychological. Overwork, fatigue, and exercising too much all create free radicals, which lower your Vitamin A level. Also, when you're too busy or tired to eat right you don't get enough beta carotene.
• You're pregnant or breastfeeding. You're passing a lot of your Vitamin A on to your baby. You need some extra for yourself—but talk to your doctor first. Too much Vitamin A during pregnancy can cause birth defects.

After several weeks without much Vitamin A in your diet, you'd start to have some signs of deficiency. One of the earliest is night blindness and other eye problems. Another sign of Vitamin A deficiency is a condition called follicular hyperkeratosis. When this happens, your epithelial tissues, especially 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 your 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 of Vitamin A can also make you more likely to get respiratory infections, sore throats, sinus infections, and ear infections.

Eating Your A's
Nutritionists today strongly recommend getting your A's the beta carotene way, through five daily servings of fresh fruits and vegetables. One medium carrot contains over 8,000 IU of beta carotene—with no toxic side effects, no fat, and only 35 calories. Remember, carotenes are the substances that give foods such as carrots, tomatoes, sweet potatoes, and apricots their vivid color. Actually, carotenes are found in practically all vegetables and fruits, 
including dark green leafy vegetables such as spinach and broccoli. The carotenes are there—you just can't see the bright reddish colors because they're disguised by the green.

Getting the Most from Vitamin A and Carotenes
Vitamin A and beta carotene are fat-soluble, which means you store them in your liver and in the fatty tissues of your body. To avoid any chance of a toxic buildup, we suggest you stick to the Vitamin A in your daily multivitamin supplement and skip any additional A supplements. 

Vitamin A and beta carotene are essential for your eyesight. Here are three reasons why:
Preventing Night Blindness
Vitamin A helps you see well in the dark. Your retina (the layer of light-sensitive cells at the back of your eye) contains large amounts of Vitamin A, especially in the tiny structures called rods that are used for night vision. If you don't get enough Vitamin A, you develop night blindness—you can't see
well in the dark or in dim light. We all lose a little of our night vision as we grow older, but Vitamin A can help slow or even prevent the loss. If you've noticed that you don't see as well at night as you used to, see your eye doctor to rule out other eye problems. If your eyes are OK otherwise, extra
Vitamin A or beta carotene might help. Discuss the right amount with your doctor before you try it.
Preventing Cataracts
A cataract forms when the lens of your eye becomes cloudy, reducing or even blocking completely the amount of light that enters your eye. At one time cataracts were a leading cause of blindness, but today simple outpatient surgery can fix the problem. But wouldn't it be better if a cataract never developed in the first place? There's solid evidence that a diet rich in carotenoids, especially beta carotene, helps prevent cataracts by mopping up free radicals before they can damage the lens.
Preserving Eyesight
Vitamin A helps prevent age-related macular degeneration (AMD). Your macula is a tiny cluster of very sensitive cells in the center of your retina. It's essential for sharp vision. As you grow older, your macula may start to degenerate, causing vision loss and eventual blindness. AMD is the leading
cause of blindness in people over 65, and about 30 percent of Americans over 75 suffer from it.

A as in Aging Skin
The cells of your skin grow very rapidly—your outer skin turns over completely in just about four weeks. All rapidly growing cells, including those in your skin, need plenty of Vitamin A. An early symptom of Vitamin A deficiency is skin that is rough, dry, and scaly. To help keep your skin smooth and supple, make sure to get the RDA for Vitamin A. This is especially important as you get older and your risk of skin cancer rises. One recent study shows that taking Vitamin A could cut your chances of getting basal cell carcinoma, the most common type of skin cancer, by 70 percent.

Carotenes and Cardiac Cases
As with cancer, so with heart disease. People who eat foods high in beta carotene definitely have fewer heart attacks and strokes. Though, just taking beta carotene supplements doesn't necessarily give you the same protection. 

Boosting Your Immunity with Vitamin A
The anti-infective powers of Vitamin A have been known ever since the vitamin was discovered.
Today Vitamin A is being used to help boost immunity in some cases—and some very exciting research suggests more uses in the future. Here's the current rundown:
• Treating measles and respiratory infections. Extra Vitamin A has been shown to help children get over the measles faster and with fewer complications. It also seems to help babies with respiratory infections. Talk to your doctor before you give Vitamin A supplements to babies or children.
• Treating viral infections. If you're low on Vitamin A you're more susceptible to illness, especially viral infections. If you're sick with a virus, extra Vitamin A in the form of beta carotene could help you fight it off.
• Preventing complications from cancer treatment. Chemotherapy and radiation therapy really lower your immunity. Very large doses of Vitamin A can help raise it again, but the amounts needed are too toxic to be used for long. In animal tests, large doses of beta carotene boost the immune system without the toxic danger. It's still too soon to tell if this will work in humans.
• Boosting immune cells. Large doses of beta carotene may help increase the number of infection-fighting cells in your immune system. This could be very beneficial for AIDS patients and anyone whose immune system is depressed.
Research continues on the benefits of Vitamin A and beta carotene for your immune system. We believe that the future will bring solid evidence that these nutrients can help not only immunity but many other health problems as well.

The Least You Need to Know
• You need Vitamin A for healthy eyes, cell growth, and a strong immune system.
• Your body converts the beta carotene found in many fruits and vegetables into Vitamin A as needed.
• Beta carotene is also a powerful antioxidant that can help protect you against cancer and heart disease.
• The adult RDA for Vitamin A is between 800 and 1,000 RE (4,000 to 5,000 IU). There is no RDA for beta carotene, but 15 mg is often recommended.
• Vitamin A can be toxic in large amounts—don't exceed the RDA. Beta carotene is safe even in very large doses.
• Foods high in Vitamin A include eggs, milk, liver, and meat.
• Foods high in beta carotene include orange, yellow, and red fruits and vegetables such as cantaloupes, tomatoes, carrots, and butternut squash. Potatoes and dark green leafy vegetables are also high in beta carotene.


Post a Comment