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Deficiency Diseases and Good Nutrition
Vitamin A (retinol)
C20H30O
Vitamin A got the name retinol, because it is involved in vision (retina), and is an alcohol. The retina is a layer of tissue on your eye. Light travels through your pupil, to the back of your eye, where it hits rods and cones. The rods are responsible for your perception of dim light and the cones are responsible for your perception of bright light and colors. They perform this function with the help of vitamin A, which is inside the rods and cones. The molecule vitamin A has many chemical double bonds. One of A's double bonds changes slightly and then reacts with the protein opsin, to make rhodopsin. When light hits this new compound, the double bond changes back to the way it was, and stimulates a nerve impulse to be sent to the brain. Without vitamin A, the nerve impulse would never be sent and you would not be able to see this screen.

This is why people who are heavy drinkers often have problems with their vision. Ninety percent of all the vitamin A in your body is stored in the liver. Alcohol kills your liver, and not as much A can be stored there. Alcohol also makes you urinate a whole lot of vitamins, including A. If you are a heavy drinker and cannot cut back, you might consider eating more foods rich in vitamin A.

Foods High in Vitamin A

Liver, beef, 3 oz.             9011 RE
Sweet potato, baked, 1 small   2488 RE
Carrot, raw, 1                 2025 RE
Spinach, cooked, 1/2 cup        875 RE
Squash, butternut, 1/2 cup      857 RE
Cantaloupe, 1/4 melon           516 RE
Apricots, dried, 8 large halves 253 RE
Milk, 2%, 1 cup                 140 RE

Now you might be wondering what a RE is. It stands for retinol equivalent. Carrots, and all plants for that matter, actually don't have any vitamin A in them; they contain carotene. Meat is the only food source that contains vitamin A. Your intestinal mucosal cells can turn the carotene into vitamin A. There are many types of carotenes, and they all make different amounts of the vitamin. Your body can convert 1/6 of the beta-carotene (most common and easiest to convert) you eat into vitamin A, and your body can absorb about 1/3 of that vitamin A. Carotene and vitamin A can be measured in the same units with retinol equivalents. For example, 1 RE = 1 microgram of retinol (animal vitamin A); 1 RE = 6 micrograms of beta-carotene (most common plant vitamin A); 1 RE = 12 micrograms of other provitamin A carotenoids (plant vitamin A).

Age          Recommended Dietary Allowance
Infant 0-1                 375 RE
1-3                        400 RE
4-6                        500 RE
7-10                       700 RE
11+ (men)                 1000 RE
11+ (women)                800 RE
   Pregnant                800 RE
   Lactating 1st 6 months 1300 RE
             2nd 6 months 1200 RE

Vitamin A has many functions in the body. As we already discussed, it plays a major role in vision. Night vision can especially be improved by an increase in vitamin A intake The rods in the back of your eye help you to see in dim light and they cannot function correctly without vitamin A. People who drink heavily run the risk of getting cirrhosis (fatty deposits in the liver), which lowers the liver's ability to store vitamin A. That's why, many times, people who drink a lot have cloudy vision. If their intake of vitamin A increases, the cloudy vision can be cured. If heavy drinkers don't get an increase in A, then irreversible damage can be done.

Vitamin A also helps in bone growth. Did you know your bones are growing all the time? Bone molecules are constantly being moved in and out of your skeleton, as needed. In fact, every 7 years you get a new skeleton. Therefore, it is very important to keep your bones healthy. Phosphate and sulfate are two of the bone molecules that are vital to your skeleton's health. Your body cannot absorb adequate amounts of these two molecules when you're not eating enough vitamin A. (Surrounding nutrients from the diet have a huge effect on how much vitamin A, and all other nutrients your body will actually absorb.) Not only does vitamin A help supply bone materials, but it directs those materials to where they should be placed. Some of the cells in your bone are equipped with enzymes to break bone down. These enzymes are released with the help of vitamin A. In this way, the bone that shouldn't be there is broken down, leaving room for new bone growth to occur.

Vitamin A is needed in the conversion of cholesterol to sex hormones. Without vitamin A, the outer covering of ovaries in women, and the prostate gland in men stops producing mucus and sex hormones. The covering hardens (no mucus) and cannot function properly (no sex hormones). A domino effect comes into action and your whole reproductive system is in danger. Because of this, men's sperm count can decrease, and women's fertility can go down if they are not eating enough A. Women can experience a reduction in sexual desire, lower fertility, and more problems with the delivery of their children. (IMPORTANT: Vitamin A will not increase fertility or sperm count, unless vitamin A deficiency is the reason for the problem. This is almost impossible if you are eating a reasonable diet. Do not try to treat yourself. Go to the doctor.)

Vitamin A not only causes reproductive cells to secrete mucus, but also causes most other cells in your body to secrete mucus. This mucus protects the cell from invading bacteria and viruses. This is an important part of the immune system and can even protect against cancer. Some doctors and scientists think that some forms of cancer are caused by viruses. A virus is nothing more than DNA wrapped up in protein. This virus gets into your normal, healthy cells and forces it to produce the new virus's DNA instead of its own. That's how viruses grow. (CANCER = Cell's DNA mutates and starts reproducing itself at a dangerous rate. These cells do not perform their designed function; they just reproduce and hinder the organ they are in. This is especially dangerous when the mutated cells spread throughout the body, stopping many organs from functioning properly.) When the cell membranes are coated in mucus, they stay intact longer, extending the cell life, and keeps you looking young.

Vitamin A is a fat soluble vitamin. That means it is eaten, absorbed, transported and stored with fat. You must be careful when cutting out a lot of fat in your diet, not to cut out the A and all the other fat soluble vitamins. Even if you eat a healthy diet, you may be getting less vitamin A than you think. Processing takes vitamin A out of foods, and additives kill it. Most refined foods are much lower in vitamins than "the real thing". Cooking can also render much of the vitamin A in foods useless. You can get more carotene from steamed carrots than raw, though. This is because the carotene is contained in the cell wall, (tough covering over the cell membrane; only plants have cell walls and membranes, animals actually only have cell membranes). The wall of a cell is indigestible unless you "loosen it up" by steaming the carrots. Boiling, however, makes A inactive. You should be careful how you prepare your foods, so you can get the full amount of vitamins possible.

There are also circumstances where your body needs more vitamin A than at other times. When your body is under physical stress, like polluted air or foods, you use up more A to protect yourself against the harmful chemicals inside your body. When under emotional stress you need more A, because your body doesn't absorb as much of it in the first place.

Your body reacts to a deficiency in vitamin A with brittle nails that grow slowly, and don't glow pink underneath. You also can be afflicted with night blindness, cloudy vision, ulcers of the cornea, and in extreme cases, blindness. Vitamin A helps to keep your tissues soft, because it encourages mucus secretion of the cells. When there isn't enough A, the tissues harden (keratinization). Your digestive and respiratory tracts can harden, making it very hard for those systems to work correctly. Your skin can also be keratinizaed. The hair folicles get plugged with keratin (insoluble protein, also the main constituent of hair and nails) and resembles goose flesh. The first to be afflicted is the forearms and thighs. On the other hand, if you get too much A, you will experience fatigue, restlessness, nausea, vommitting, headaches, skin rash, dry scaly lips, hair loss, brittle nails, weight loss, and liver ad spleen enlargement. Carotene from plants isn't toxic, because your body only changes what it needs to vitamin A. You may get alarmingly yellow-orange skin though. To get a toxicity, you'd have to take 100,000 RE every day for six months. Probably the only way you would do this is through supplements, so be careful with those supplements. You don't need them anyway if you eat a ballanced diet of wholesome foods.

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Revised: 14 Sep 99