Asparagus [© Comstock](Asparagus [© Comstock] )

Vitamin deficiencies aren't what they used to be.

A hundred years ago, lacking a nutrient such as Vitamin C in your diet might have caused a pale complexion and a scurvy diagnosis. Today, however, acute vitamin deficiencies are not common in the United States. Instead, nutrition experts say, it's more likely that busy, fast-food-loving Americans aren't getting adequate daily intakes of some vitamins or minerals, which might not make them sick but can leave them feeling less than 100 percent.

Taking a supplement may be a cheap and safe way to confront that problem, and researchers are currently looking to see what other potential benefits there might be to a vitamin regimen.

But make no mistake: Vitamins can't do everything.

In Pictures: 9 Vitamins You Need

"Here's the risk," says Christopher Gardner, assistant professor of medicine for the Stanford Prevention Research Center at the Stanford University School of Medicine. "You have an Egg McMuffin for breakfast, a Whopper for lunch and a Big Mac for dinner--then, before bed, you pop a pill and say, 'Whew, I'm OK.' The point is to eat a balanced diet and, to hedge your bets, maybe take supplements."

The reason why so many of us aren't getting all our recommended daily allowances of vitamins and minerals is simple. We eat the wrong things, day after day.

"The cause is very clearly the overuse of highly processed foods," says Katherine Tucker, professor at the Friedman School of Nutrition Science and Policy at Tufts University.

Though not the easiest, changing your diet is considered the best solution. Most vitamins and minerals are available in a buffet of different foods. Folate, which prevents birth directs during pregnancy, is available in fortified cereals, as well as in spinach and black beans. Calcium--important for bone strength--is easy to get in milk, fortified orange juice, cheese, yogurt and tofu.