The researchers' review of studies on vitamins and disease revealed that insufficient levels of folic acid increases a person's risk for neural tube defects. A low intake of Vitamins B6 and B12 raise the risk for cardiovascular disease and colon and breast cancer. In addition, a shortage of vitamin D boosts the chance of osteoporosis and bone fractures, while evidence suggests that suboptimal intake of vitamins A, E and C may increase the risk of several other chronic diseases.

The experts do stress that vitamin supplements are no substitute for eating right. Instead, people should strive to eat at least five servings of fruits and vegetables daily as part of a low-fat, fiber-rich diet. Foods, unlike supplements, contain thousands of chemicals that may promote health, the researchers write. As a result they recommend multivitamins be taken in addition to, not in place of, a well balanced diet.

Before You Take a Multivitamin People that already take a multivitamin and those contemplating adding one to their routine should talk to their doctors, warn researchers. Some vitamins can interfere with the effectiveness of certain medications, while excessive doses of others can have serious side effects. For example, women who are trying to conceive should avoid taking too much vitamin A, and need more folate than other individuals.

Most good multivitamins contain approximately 100 percent of the daily-recommended value of all vitamins and minerals.