1. Eat a healthy diet. A multivitamin provides some insurance against deficiencies but is far less important for health than the healthy food patterns described on this website. Choose a diet rich in fruits, vegetables, whole grains, nuts and healthy oils, and low in red meat and unhealthy fats--let the Healthy Eating Pyramid and Healthy Eating Plate be your guides.
2. Choose a daily multivitamin. A daily multivitamin is an inexpensive nutrition insurance policy, and for most people, the benefits seem to outweigh the risks. Try to take one every day.
3. Think about D. In addition to its bone health benefits, there's growing evidence that getting some extra vitamin D can help lower the risk of colon and breast cancer. Aim for getting 800 to 1,000 IU of vitamin D per day--this likely will require an extra vitamin D pill, in addition to your multivitamin. Many people, including those who spend too little time in the sun, may need more. As always, it's a good idea to discuss use of supplements with your doctor, and he or she may want to order a vitamin D blood test. For more information, see the vitamin D section of The Nutrition Source.
4. Say no to "megas." In general, avoid mega-dose vitamins and mega-fortified foods. Vitamin D is an exception, as many people need more than the Recommended Dietary Allowance (RDA). A standard multivitamin also has a day's worth of folic acid, so if you are taking a daily multivitamin you should avoid foods that have high amounts of folic acid added to them.
5. Avoid "super" supplements. Don't be swayed by the wild health claims of the many health supplements advertised on TV and the Internet. If they sound too good to be true, you can be sure they are.
Read more
Keep the multi, skip the heavily fortified foods: Why you should keep taking a daily multivitamin but skip foods that are heavily fortified with folic acid.
Antioxidants: Beyond the hype: What's the buzz around antioxidants--and what's the evidence?
Supplement studies: Sorting out the confusion: How to make sense of the media hype around supplements.
Nearly 40 percent of adults in the U.S. take a multivitamin to ensure good health. A recent study of women in Iowa suggests that this daily habit may be doing more harm than good. A closer look, however, reveals major flaws in the study--and offers reassurance that taking a daily multivitamin may still be a smart move. 
