Americans loves their vitamins. Walk into a supermarket or drug store and you'll find shelves full of single or multivitamins. They come in a variety of formulas too -- for women, men, seniors, children, weight loss, heart health and more. No matter who you are, there's a supplement marketed "just for you."

Why are supplements so popular? Many people see them as an affordable, easy means to living longer, preventing disease and improving health. It's easy to understand why -- hardly a week goes by without news about an antioxidant that prevents cancer, a vitamin that wards off Alzheimer's, or an herb that reduces your fatigue.

But a recent review of major studies found that people taking antioxidant supplements lived no longer than those who didn't. In some comparisons, the people using supplements died sooner than people who did not take them. These results have added to the longstanding debate over the effectiveness of supplements.

So what should you do? Should you keep taking vitamins or leave them on the store shelf?

Supplement basics

Let's start with the importance of vitamins, antioxidants and minerals. Vitamins are necessary for nearly every process in your body, like growing, replacing cells and fighting disease. Antioxidants are substances (found in some vitamins) that help your immune system and protect cells from damage. Your body uses minerals to perform functions like building bones and maintaining fluids.