Taking vitamins and minerals seems to fall within a gray area -- giving your body what it needs by taking nutritional supplements can certainly benefit you, but knowing how to assess your exact requirements can be difficult. Without testing, it's hard to say which vitamins and minerals you personally need. But these general guidelines apply if you're in one of these groups:

Infants and children

Infants who are breast-fed by healthy mothers receive enough vitamins except, in some cases, vitamins K and D. Human milk has low levels of K, and the newborn's immature intestinal tract may not produce enough to supply sufficient amounts to the baby. Most babies are given an injection of vitamin K at birth.

Infants who are breast-fed by malnourished women or by those who lacked sufficient exposure to sunlight may be deficient in vitamin D. In these cases, vitamin D supplements of 200-300 IU are recommended. Formulas are required to contain sufficient vitamins and minerals. One study suggests that when infants under 1 year of age take vitamin supplements, it may help protect them from developing Type I diabetes later in life.

Smokers

Smoking interferes with absorption of a number of vitamins; most importantly, vitamin C. Folic acid supplements may be important for all smokers. When smokers take high doses of antioxidant vitamins, however, it may actually be harmful, especially beta-carotene. Instead of taking supplements, most smokers should be sure their diets are rich in fresh fruits, vegetables and whole grains. And it goes without saying that it would help to stop smoking. But some people just enjoy it way too much to quit, so at the very least extra attention should be paid to giving the body nutrition that will support it.

Alcoholics

Alcoholics often suffer from multiple vitamin deficiencies. The most dangerous deficiencies are from vitamin C, vitamin B1 (thiamin), folic acid, vitamin B6 (pyridoxine) and vitamin B2 (riboflavin).

Older adults

Deficiencies of vitamins and minerals have been observed in almost one-third of elderly people, who often fail to eat regular, balanced meals. Multiple drug regimens that are often prescribed for elderly people may prevent absorption of some vitamins. The elderly, particularly if they are not exposed to sunlight, may have vitamin D deficiencies. They also may have low levels of vitamin B12, vitamin B6 and folic acid. Older adults showing signs of dementia should be checked for vitamin B12 deficiencies, as well as other disorders that cause mental disturbances.

One study reported that the immune systems of elderly people might benefit from vitamin E in levels higher than the daily recommended dosage. It should be noted, however, that metabolism slows down as a person ages, and in elderly people it takes longer for the liver to eliminate drugs and vitamins from the body. The effect of some vitamin supplements, therefore, may be intensified. Dosage levels of vitamin A, for instance, which might be harmless in a younger adult, could be toxic in an elderly patient. Nevertheless, experts are increasingly recommending extra vitamins and minerals for older people.

Dieters and vegetarians

People on weight-reduction diets of fewer than 1,000 calories a day should probably take multivitamins and should also check regularly with a physician. Vegetarians who do not eat dairy or meat products may need riboflavin, vitamin D and vitamin B12 supplements. Those who eat eggs and dairy products need only watch their iron levels to guard against hair loss and other problems caused by iron deficiency.

Pregnant and breast-feeding women

There are so many things to do during pregnancy, some women who are pregnant or breast-feeding may miss the fact that they generally need additional vitamins, and that B vitamins are particularly important. Folic acid reduces the risk for neural tube defects and possibly facial abnormalities, such as cleft palate, in newborns. Multivitamins also appear to protect against certain congenital heart defects. In order to be protective, however, both folic acid and multivitamin supplements must be taken before a woman actually becomes pregnant. Folate levels, even in a healthy diet, may not be protective enough for pregnant women, and so supplements are needed.

The RDA for folic acid prior to conception and during pregnancy is 400 mcg. During breast-feeding, however, between 260 and 280 mcg is recommended. Choline, another B vitamin, is also essential for pregnant and nursing women -- 450 mg during pregnancy and 550 when breast-feeding. Vitamin B6 may help improve morning sickness. Although one study suggested that if pregnant women take vitamin K supplements, their infants might not need the required injection of this vitamin after birth, supplements of vitamin K during pregnancy are not currently recommended.

Some women have low vitamin A reserves in their livers, but it's important to note that too much vitamin A significantly increases the risk for birth defects. Even daily amounts of 10,000 IU of vitamin A in supplements and food (an amount not far above the RDA level) can pose a danger. Experts recommend that pregnant women take in no more than 8,000 IU per day and avoid eating liver.

For more information on vitamins, read these in-depth fact sheets:

Can too much of a good thing be a bad thing? With some vitamin supplements, yes. Taking megadoses of certain vitamins can actually endanger your health by causing the following:

Vitamin A: blurred vision, headaches, fatigue, damage to liver and nervous system

Vitamin D: kidney stones, high blood pressure, deafness

Vitamin K: skin yellowing in infants

Vitamin B3 (Niacin): ulcers, abnormal liver function

Vitamin B6: high doses produce dependency

Vitamin C: high doses cause dependency, diarrhea

Please note: The information on this page is not meant to take the place of professional recommendations. See your doctor or a nutritionist to determine the supplements that are right for you.

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