In a new statement, the US Preventive Services Task Force concludes that there is not enough evidence from randomized controlled trials for preventive effects of vitamin, mineral and multivitamin supplements in the areas of cancer and cardiovascular disease. Experts criticize that nutrients are not drugs and cannot be expected to show significant effects in clinical studies on multifactorial diseases.
To assess potential beneficial and harmful effects of the use of vitamin, mineral and multivitamin supple- ments, the US Preventive Services Task Force (USPSTF) analyzed the results of four randomized controlled trials and one cohort study on the prevention of cardiovascular disease or cancer (1). The USPSTF concluded that the current evidence is insufficient to recommend the use of single- or paired-nutrient supplements for cardiovascular disease and cancer prevention. While the USPSTF found adequate evidence that supple- mentation with vitamin E represents little or no significant risk, supplementation with beta-carotene increased risk for lung cancer in persons who are at increased risk for lung cancer, such as smokers.
Experts commented that micronutrients are not drugs; they do not mitigate, treat, or prevent chronic diseases. Vitamins and minerals are required for life and the use of supplements can insure an adequate nutrient supply for people who fail to meet their nutritional requirements from food alone (2). Their goal is to help improve or maintain overall health by supplementation (3, 4). In addition, randomized controlled trials have many shortcomings when it comes to investigating nutrient effects: for example, there is no true placebo group as the diet will always provide some of the nutrients under investigation and the nutrient may be given to individuals with an already adequate level of the nutrient so that no additional effect can be expected (5). Moreover, most of the studies did not consider the genotype in assessing the potential micronutrient benefit. Even when drugs are being evaluated with the intent of preventing cancer, there are few certainties, and a drug’s efficacy can depend on cancer type and genotype of a patient. With regard to the harmful potential of supplements, the long-term intake of very high doses of beta-carotene has been found to increase risk of lung cancer in smokers. Consequently, smokers are advised not to supplement with beta-carotene. It would make even more sense to advise against smoking, the experts added.
