In recent years, people in the United States have forked over more than $12 billion annually for vitamin and mineral supplements, presumably to bolster their health. That’s a hefty sum—but a new research review suggests that when it comes to improving your health, that money may be better spent.

The research review, published Dec. 17, 2013, in the Annals of Internal Medicine, turned up “insufficient evidence” that taking supplements prevents cancer or heart disease, the two leading causes of illness and death in the U.S.

Funded by the Agency for Healthcare Research and Quality, a research arm of the U.S. Department of Health and Human Services, the review looked at data from 26 previous studies that together had enrolled more than 300,000 healthy people, ages 22 to 77—none of whom had been previously diagnosed with cancer.

Resveratrol Does Not Reduce Deaths, Heart Disease or Cancer​​​

Study looks at effect of resveratrol on overall health.​

A study that looked at the effect of resveratrol on overall health in nearly 800 women and men age 65 and older participating in the Aging in the Chianti Area study in Tuscany, Italy, found that those who ate a diet rich in resveratrol did not live any longer than those whose diets supplied lower levels of resveratrol. They also were just as likely to be diagnosed with cancer or heart disease.

Interest in resveratrol grew after laboratory studies found it had anti-inflammatory effects and increased the life span of mice. Studies in small groups of people also suggested it could be beneficial. The new epidemiological study, published online May 12 in JAMA Internal Medicine, measured resveratrol intake by analyzing levels of its byproduct in urine samples and followed the participants for nine years.

Food and drinks that have been touted for their health benefits because they contain resveratrol include red wine, dark chocolate, peanuts and certain berries. According to the researchers, annual sales of resveratrol supplements have reached $30 million in the U.S. alone.

No matter how they looked at the data, says physician Stephen P. Fortmann, a researcher at the Kaiser Permanente Center for Health Research in Portland, Ore., who led the study, his team was unable to identify a group that would benefit from taking vitamin or mineral supplements. Two studies included in the review did report lower cancer incidence rates among men who took multivitamins for 10 years, but not enough evidence was found to link the vitamins to the benefit.

The research review also noted that supplements can potentially cause harm. For example, a cancer prevention study in nearly 30,000 male smokers found that those who took beta-carotene were more likely to develop lung cancer than the men who did not take it. Previous studies had suggested the supplement might reduce lung cancer risk.

Colleen Gill, a registered dietitian at the University of Colorado Cancer Center in Aurora who specializes in oncology nutrition, says cancer patients often take supplements because they think they will make their cancer treatments more effective. All too often, she says, these patients have been led to believe that supplements can “make all the difference in the world” when, in fact, they offer no benefit and may interfere with cancer treatment.

The critical issue isn’t quantity of vitamins, she says, but quality of diet. For a person not deficient in any nutrients, supplementation is probably unnecessary, as the latest review suggests. But it’s not a black-and-white issue, she says, adding, “For cancer patients who are not eating well, taking a multivitamin or supplement may not be wrong. It may be helpful.”