Taking vitamin E or beta-carotene does not appear to reduce the risk of cancer or cardiovascular disease, according to a new review from a government-appointed panel of experts.
However, there isn't enough evidence to say whether other vitamins or minerals (such as vitamin D, calcium and selenium) or multivitamins reduce the risk of these two conditions, according to the review from the U.S. Preventive Services Task Force.
Although the effect of vitamins is unclear, some studies do suggest that a healthy diet reduces the risk of cancer and heart disease, the researchers said. [10 Do's and Don'ts to Reduce Your Risk of 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," said Dr. Michael LeFevre, co-chair of the task force. Doctors should also consider the latest research as well as their patients' preferences when discussing vitamin supplements, LeFevre said.
The recommendations from the review apply to healthy adults without nutritional deficiencies, but do not apply to women who are pregnant or plan to become pregnant. (It is recommended that these women take folic acid supplements.)
The task force reviewed about 30 studies looking at the effects of vitamins and multivitamins on cancer and cardiovascular disease.
Many studies on individual vitamins showed no benefit, but there were too few studies on any single vitamin to make a definitive conclusion about the substances' benefits or risks, the task force said.
But there were two exceptions: vitamin E and beta-carotene. For Vitamin E, studies showed that taking the supplement did not prevent cancer or heart disease, but also was not harmful, overall. For beta-carotene, taking the supplement was linked with an increased the risk of lung cancer among smokers.
Although some research suggests that multivitamins may reduce the risk of cancer, these studies tended to involve specific groups of people, and more research is needed before the findings can be applied to the general population, the task force said.
The new review is an update to the task force's 2003 recommendations. At that time, there was not enough evidence to assess the benefits or harms of most vitamins, but taking beta-carotene for the prevention of cancer or heart disease was not recommended.
The Academy of Nutrition and Dietetics says that, although multivitamins may be useful in helping some people meet recommended levels of certain nutrients, there is no evidence that the supplements are effective at preventing chronic diseases.