Some researchers believe they may not work at all. Experts say there's an easy way to make sure you're getting the vitamins you need without depending on a pill.

Heart attack, cancer and Alzheimer's disease are illnesses that many hope can be delayed or prevented by taking a vitamin supplement. Several large studies released this year may cause consumers to reconsider.

"It's probably not harmful to take a multivitamin if you want to but you may be wasting your money," said dietician Ginnie Collins.

Dieticians say you'll get more bang for your buck by shifting your focus from taking a pill to eating healthy foods. For example, one cup of cantaloupe gives you more than 100 percent of your Vitamin C needs.

"Oranges have lots of Vitamin C; beans have lots of protein; broccoli has lots of Vitamin C; dark green leafy vegetables have lots of folate and calcium," said Collins.

Experts say consumers should stock their grocery carts with the colors of the rainbow: red, orange, yellow, green, blue, and purple.

"Nature provides us with all these colorful vegetables and fruits, and, if we eat them every day, than we're going meet the majority of the needs that we have," said Collins.

Some people need supplements; for example, pregnant women need extra folic acid, and some elderly people need more Vitamin B12. These are exceptions to the rule; for the majority, the sure way to stay healthy is a colorful diet.

Representatives from the vitamin industry say the best advice for consumers is to engage in a lifetime of healthy habits -- like not smoking, maintaining a healthy weight, eating a well-balanced diet and appropriately supplementing with vitamins.