One in three Americans takes multivitamins and minerals, spending a total of some $21 billion on supplements every year. But a new analysis suggests that at least when it comes to heart health, multivitamins and minerals aren't worth it.

Research published in an American Heart Association journal looked at 18 previous studies on multivitamins, tracking more than 2 million people for an average of 12 years.

They found multivitamins do not prevent heart attacks, strokes, or death from cardiovascular disease.

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"Americans who are taking these supplements presumably because they're concerned about their health would be better served by spending their money on good nutrition in the form of a healthy diet," Dr. Erin Michos, a cardiologist at Johns Hopkins University, told CBS News.

Researchers say the best vitamins and minerals come from the produce aisle, not a pill bottle. Fruits and vegetables already have a proven track record in lowering the risk of heart disease and stroke.

Dietary supplements are also not FDA-approved for safety or effectiveness.

"People shouldn't be under the misconception that just because you can get these over the counter that they're safe. Each year, an estimated 23,000 individuals are seen in emergency departments across the country due to adverse effects from different supplements," Michos said.

In response, the Council on Responsible Nutrition, a supplement trade group, said, "multivitamins fill nutrient gaps in our less-than-perfect diets" and "are not intended to serve as magic bullets."

The group also says that multivitamins help low-income Americans combat insufficient nutrient levels for less than a dime a day.