How Nutrition Works

Vitamins Not To Overdo

Some vitamins can actually be harmful is you ingest too much. Here's a list of what to look out for:

Vitamin A. Don't make the mistake of substituting preformed vitamin A (called retinol) for beta-carotene in the hopes of preventing disease. Vitamin A is toxic in large amounts, over 50,000 international units (20,000 international units in children). Though toxicity usually results from oversupplementation, liver contains extremely high levels of vitamin A; eating too much too often is not a good idea.

Although vitamin A is vital to eyesight and immune function, too much vitamin A also causes vision problems and a weakened immune system that invites infection. If a pregnant woman takes too much, it can cause birth defects in the fetus.

This is not a nutrient to fool around with. Excess vitamin A can cause blurred vision, headaches, nausea, achy bones, or irritability. Particular caution for seniors: As you age, your liver is less able to remove vitamin A from the bloodstream, making toxicity a bigger worry. Supplements with preformed vitamin A should not contain more than the DRI. If you feel that you need a vitamin A supplement, it's best to take beta-carotene, which can be converted to vitamin A in the body.

Vitamin D. This is another nutrient that demands respect. Toxic levels are only five times the DRI. Children are particularly susceptible to a toxic reaction to vitamin D, which causes blood calcium levels to soar -- a dangerous condition.

Seniors often don't get enough vitamin D. They are not in the sun a lot, and when they are outside, their skin requires more time to convert vitamin D to its active form. Often, they don't drink much milk either. If this describes you, ask your doctor about taking a combination calcium-vitamin D supplement, or a multivitamin-mineral supplement. Just be sure you take only one of these options and that the amounts don't exceed 100 percent of the DRI.

Niacin. As its nicotinic acid alter ego, this B vitamin becomes powerful enough to lower high cholesterol levels. To do so, it must be prescribed in high doses (more than 1,000 milligrams), which can cause nicotinic acid flush -- an immediate redness and swelling of the face and neck, often accompanied by itching, headache, and nausea. This side effect lessens with use, but taking this supplement should be monitored by your doctor. Heartbeat abnormalities are more serious. People with diabetes are advised to stay away from high doses of nicotinic acid because it can raise blood sugar to dangerous levels.

Vitamin B6. This nutrient was once thought to be immune to toxicity. It took until the 1980s, when it became popular to take vitamin B6 supplements in ever larger amounts, to discover the upper limit of its safety. Here's what caused it to finally lose its cachet: nerve damage from doses as low as 500 milligrams a day, more commonly from amounts over 2,000 milligrams. Fortunately, the damage is reversible if the supplements are stopped at the first sign of tingly or numb extremities or trouble walking.

Iron. Like vitamin A, this Jekyll-and-Hyde nutrient is on both lists. Many people don't get enough, but too much can be dangerous, too. You hear a lot more about having iron-poor blood than you do about iron overload (or hemochromatosis), which can develop in people who inherit a gene that causes the body to absorb too much iron. This potentially fatal condition threatens a surprisingly large number of people -- 1 in every 250 -- mostly men and postmenopausal women, because their iron needs are lowest. They are best off avoiding supplements with iron.

Iron supplements also threaten children; they are the leading cause of accidental pediatric poisoning. It takes only five tablets of high-potency iron to kill a child under age six. Childproof caps are a must, though recent cases have been caused by caps left off or not tightened. Don't overlook grandparents' homes, where caution may be less vigilant and accidents more likely.

Antioxidants to the Rescue

If you haven't heard of antioxidants by now, you're just not paying attention. They're the hot topic in disease prevention. Antioxidants aren't new, however. They've been around all the time; we just weren't smart enough to appreciate them. Now we know they're like secret service nutrients that fight against a form of biological damage called oxidation -- a chemical reaction that occurs when oxygen latches onto substances that have left themselves exposed to attack.

With oxidation come the inevitable party crashers -- free radicals -- that do harm to whatever cells are in their way. This destruction escalates into chain reactions that eventually can even alter the genetic makeup of cells. Scientists now think free radicals are formed by pollution, cigarette smoke, even sunlight. It's been said that we have never needed antioxidant protection more than we do now.

In addition to their regular duty, several nutrients act as antioxidants. The best-known of these are vitamins C and E and beta-carotene (though beta-carotene's primary benefits may not stem from its antioxidant role). In addition, selenium and copper are essential components of enzymes needed for antioxidants. Other nutrients now being credited with antioxidant properties include riboflavin, magnesium, manganese, zinc, and another carotenoid called lycopene.

Research has shown that antioxidants are beneficial to health. They protect against chronic diseases like cancer and heart disease, and they also boost immune function and combat aging, which may simply be the body's response to repeated assaults by free radicals.

But there is still disagreement over just how important antioxidant supplements are. It is recommended to get antioxidant nutrients from foods, such as fruits and vegetables. Vitamin C appears to be a jack-of-all-trades, with links to lower rates of cancer, heart disease, and cataracts. Beta-carotene, on the other hand, has been riding a roller-coaster of evidence as to whether it protects against certain cancers and heart disease.

Despite mostly strong research results, particularly with lung cancer, some are skeptical of beta-carotene's role because most of the evidence came out of studies with fruits and vegetables, not simply beta-carotene supplements. It has become increasingly clear that other substances in fruits and vegetables may be just as important.

If you're not getting your necessary vitamins and minerals you might consider supplements, which will be discussed in the next section.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider