(NBC News) More than half of Americans take some sort of vitamin supplement, spending billions of dollars on the pills each year.
But a new report confirms what some doctors have been saying for years.
There's no evidence supplements help prevent heart disease or cancer.
The reasons behind supplementation are as different as the people taking them.
But now new research suggests if you're using them to prevent two major types of disease, you may not be getting your money's worth.
"If the purpose of your vitamin supplementation is to prevent heart disease and cancer, that there isn't enough evidence right now to say conclusively that it is effective for doing that," said Dr. Kirsten Bibbins-Domingo a panel member of the U.S. Preventative Services Task Force
The new report from the U.S. Preventive Services Task Force updates its 2003 findings, stating there's still not enough evidence for or against supplementation for preventing heart disease and cancer.
This time there was enough evidence for experts to say without a doubt vitamin "E" and beta-carotene do not prevent these diseases.
In fact, the report finds beta carotene can increase the risk for lung cancer among smokers.
"This is one area where the studies are there and are clear that there are harms in this high risk group," Bibbins-Domingo said.
Representatives for the vitamin industry say many Americans rely on multivitamins, not for disease prevention, but simply to make up for nutrients they don't get from their diet.
"A multivitamin can fill those nutrient gaps and provide us all the essential nutrients we need, it really is a good insurance policy," said Dr. Douglas Mackay of the Council of Responsible Nutrition.
Experts say patients should talk to their doctor about which supplements, if any, they should take.
These recommendations are open for public comment until the beginning of December then the task force will release its final statement.