There is little scientific evidence to suggest that taking a multivitamin supplement helps Americans ward off chronic diseases, including most cancers and cardiovascular disease, according to a study by researchers at the Johns Hopkins Bloomberg School of Public Health and the Johns Hopkins School of Medicine.
Their conclusions are based on a review of previously published scientific studies on multivitamins. The researchers presented their findings at the National Institutes of Health's State-of-the-Science Conference on Multivitamin/Mineral Supplements and Chronic Disease Prevention held in Bethesda, Md., May 15 to 17, 2006.
Background information contained in the study stated that over-the-counter multivitamin and mineral supplements are commonly consumed by Americans in the hope of promoting overall health and preventing chronic disease. Multivitamin/mineral supplements typically contain 10 or more vitamins and minerals at varying doses.
"We found very little scientific evidence to demonstrate that multivitamin use prevents chronic disease. The only possible benefit was seen for cancer prevention in people with poor nutrition," said Han-Yao Huang, PhD, MPH, assistant professor in theDepartment of Epidemiology at the Johns Hopkins Bloomberg School of Public Health and the principal investigator of the review project conducted at the Johns Hopkins Evidence-Based Practice Center.
Using an objective, comprehensive and reproducible review approach, Huang and her colleagues identified only five clinical trials that specifically examined the effects of routine use of multivitamin supplements in preventing cancer, hypertension, cardiovascular disease or age-related eye disease. No clinical trial looked at other chronic diseases. One large clinical trial conducted in approximately 30,000 nutritionally deprived Chinese showed that a beta-carotene, vitamin E and selenium supplement reduced the risk for gastric cancer and overall cancer deaths. Another clinical trial in approximately 13,000 French showed that a vitamin C, vitamin E, beta-carotene, selenium and zinc combination reduced the risk of cancer in men, but not in women. Blood levels of certain nutrients suggest that women in the French trial may have consumed more fruits and vegetables than men. They were also less likely to be smokers. Participants in these clinical trials used the study supplements for 5 to 8 years. Both trials used low doses (one to two times the U.S. Recommended Daily Allowances, the average daily dietary intake level sufficient to meet the nutrient requirement of nearly all apparently healthy individuals). In the few studies that looked at the effects of antioxidant supplement use on hypertension, cardiovascular disease or cataracts, no consistent significant benefit was found. However, one study showed that combined antioxidants and a high dose of zinc slowed the progression of age-related macular degeneration in people who already have the disease.