Getty Images / Getty Images

Americans spend nearly $12 billion each year on vitamin supplements, hoping they will steer us away from diseases like cancer and heart attacks. But it turns out they’re just a drain on our wallets.

Should healthy people take supplements to keep them healthy? A panel of experts convened by the government, the U.S. Preventive Services Task Force, says that for most vitamins and minerals, there is not enough evidence to determine whether the pills can lower risk of heart disease or cancer. And when it comes to beta-carotene (found in carrots and tomatoes) and vitamin E, there is no evidence that they can protect against either heart disease or cancer; in fact, beta-carotene use contributed to an increased risk of lung cancer in smokers.

That will come as a surprise to most Americans, who pop pills of omega-3 fatty acids hoping to fend off a heart attack or down vitamins C and E, which are high in antioxidants, to counteract the free-radical damage that contributes to cancer. “In the absence of clear evidence about the impact of most vitamins and multivitamins on cardiovascular disease and cancer, health care professionals should counsel their patients to eat a healthy, well-balanced diet that is rich in nutrients. They should also continue to consider the latest scientific research, their own experiences, and their patient’s health history and preferences when having conversations about nutritional supplements,” task-force member Dr. Wanda Nicholson said in a statement.

(MORE: Vitamin D and Calcium Supplements May Not Prevent Fractures)

The panel based its conclusion on a review of 26 studies, conducted from 2005 to ’13, some of which involved single supplements and others that investigated multivitamins and their relationship to heart disease, cancer and death outcomes. The review built on the panel’s previous report on supplements, in 2003, in which the task-force members said that there was not enough evidence to recommend vitamin A, C or E supplements, multivitamins or antioxidant combinations to prevent heart disease or cancer. At that time, the members also recommended against beta-carotene supplements because of their connection to a higher risk of lung cancer among smokers. In the current review, the members considered additional data on other vitamins and nutrients, including vitamins B and D, as well as zinc, iron, magnesium, niacin and calcium.

The conclusions apply to otherwise healthy people who take the supplements to prevent disease, so it’s not clear how effective, if at all, the pills can be in those at higher risk of heart problems or cancer. There have been hints, however, that the pills might not be the panacea that many people hoped they would be. In 2012, for example, a study published in the Journal of the American Medical Association showed that omega-3 supplements, touted as a powerful weapon against heart disease, did not lower risks of heart attack, stroke, or death from heart disease or any cause. Another study published in 2011 even linked vitamin-and-supplement consumption to a higher risk of death, reporting that women who took multivitamins were 6% more likely to die over a 19-year period, compared with women not taking them.

(MORE: Hold the Salmon: Omega-3 Fatty Acids Linked to Higher Risk of Cancer)

Why the takedown of vitamins, especially if they are so prevalent in good-for-you foods such as fruits and vegetables? Experts believe that the benefits of nutrients like vitamins may depend on how they are presented to the body; some may need the help of other compounds found in their natural form that are inadvertently stripped from individual pills that try to concentrate the health benefits of specific vitamins or minerals. “[T]he physiologic systems affected by vitamins and other antioxidant supplements are so complex that the effects of supplementing with only 1 or 2 components is generally ineffective or actually does harm,” write the authors in their report, published in the Annals of Internal Medicine.

They recognize, however, that their conclusions are based on relatively few studies, since few trials have addressed the question of whether supplements can prevent disease in healthy people. So the results hold only until more data become available to understand the association more completely. In the meantime, the best way to take advantage of any health-promoting effects of nutrients like vitamins and minerals is to get them in their natural state, by eating a well-balanced diet high in low-fat dairy, fruits, vegetables and lean proteins.

MORE: Vitamin E May Increase Risk of Prostate Cancer