Do you know what nutritional supplements you need?

Dozens of studies published in peer-reviewed medical journals have reported that people who either take vitamin supplements or have higher blood levels of certain vitamins, especially the antioxidant vitamins C and E and the carotene family (precursors of vitamin A), are in better health than those who don't.

For instance, various studies indicate that folate and vitamin B6 can reduce the risk of heart attack, and that vitamin C exerts a protective effect on the arteries of diabetics. Medium to high doses of vitamin C and betacarotene, as well as elevated doses of vitamin D, have been linked to a reduced risk of osteoarthritis and less pain should the osteoarthritis strike.

In a Finnish study, male smokers who took small doses of vitamin E lowered their chances of getting prostate cancer by 30 percent and lowered their risk of dying from prostate cancer by over 40 percent. What's more, American and European studies have found that lycopene, a member of the carotene family that is found in tomatoes and other vegetables, seems to help prevent prostate and colorectal cancer and possibly coronary heart disease.

While Americans spend millions of dollars annually on vitamins, minerals, herbs and other nutritional supplements, the supplement industry is unregulated by the FDA and thus does not have to adhere to strict government standards. This means that consumers may not always be buying what they think they're buying. In the worst-case scenario, tainted supplements (such as melatonin) have been known to cause illness and death.

Nevertheless, many people take their nutritional supplements every day without fail because they believe they can cure and prevent illness, raise energy levels and increase longevity. But how many of us actually understand what kind of vitamins and other supplements we need, along with knowing the unique capabilities and differences between various supplements?

"It can be difficult for individuals to correctly assess which supplements they need," says Dale Prokupek, M.D., a board-certified gastroenterologist and director of the Educational Subcommittee of the Division of Nutrition and Gastroenterology at Cedars-Sinai Hospital in Los Angeles. "Generally, it doesn't hurt to take vitamin supplements as long as you don't overconsume them," says Dr. Prokupek. "Eating a balanced diet meets the standard vitamin requirements for most people over 40," he adds, "but there are reasons to supplement certain vitamins at certain times -- for instance, supplements to help promote cognitive functions in older adults, iron supplements during exercise or as an adjunct to a strict vegetarian diet."

Some people, however, can benefit from taking vitamin/mineral supplements because they fail to consume enough crucial minerals, such as calcium, iron or selenium, in their daily diets. And how do you know if you're mineral-deficient? "Go to your primary care doctor for a serum mineral level blood test," advises Dr. Prokupek. "This is the only way to find out what an individual's mineral levels are." Whatever you do, don't design your own vitamin program without consulting your doctor.

There are two types of vitamins. The fat-soluble ones, such as A, D, E and K, are stored in the body. Then there are the water-soluble ones, such as C, thiamine, riboflavin, B6, niacin, folacin, B12, biotin and pantothenic acid.

Dr. Prokupek, who designs and personally mixes his own vitamin formulas for his patients, says that the ideal way to take vitamins is to "customize vitamin and mineral intake according to family history." For example, if an individual's family history includes a predisposition toward heart disease, high blood pressure and high cholesterol, supplementation with a heart-healthy formula including flax seed, fiber, folic acid, vitamins A, C and E, selenium and grapeseed oil might be recommended.

For individuals who want to prevent or slow the progression of Alzheimer's disease and senile dementia, a vitamin formula including B6, pyridoxine, vitamin E, phosphatidyl serine, ginkgo and other elements might be a worthwhile supplement. Besides being linked to a slower risk of colon cancer and coronary heart disease and a slower progression of Alzheimer's disease, vitamin E has also been shown to boost immunity in elderly people.

The main thing to remember when choosing supplements, says Dr. Prokupek, is to "ensure you understand your health condition and then define your goals. Your health condition," says Dr. Prokupek, "should determine which supplements you take." Another good idea, he adds, is to re-evaluate your diet. "Try and see how you might be consuming more vitamins, minerals and fiber through your food," he says. "Snacking on an apple or carrots once or twice a day is a healthy and natural way to get more vitamins and fiber."