About half of all Americans take a daily multivitamin, and in the economic downturn, people seem to be taking them even more. But taking vitamins is controversial: According to Eric Rimm, associate professor of epidemiology and nutrition at the Harvard School of Public Health, evidence shows that healthy diet and exercise are the best way to fight disease; vitamins are no replacement. If you don’t eat well and you’re stressed out, though, it could be a different story, the New York Times reports. As for cost, taking a daily multivitamin won’t hurt, unless you eat lots of fortified food. According to the newspaper, to get the most vitamin for the least money, you should take only what you need: talk to a doctor about taking a blood test to learn what might be lacking (many people, for example, would only need a vitamin D supplement). Find a good vitamin source, and keep in mind that paying more for a brand name won’t necessarily mean better quality vitamins. Experts suggest buying from well-known retailers that restock frequently, as vitamins lose their potency over time. And remember to check certification symbols: see if a product is certified by a nonprofit organization that checks for purity and quality.