A Yale epidemiologist participated in an Institute of Medicine committee which has found that antioxidants’ role in preventing chronic disease is still uncertain and large doses may lead to health problems rather than offer benefits.
The report is the culmination of a two-year study by the National Academies Institute of Medicine’s Committee on Scientific Evaluation of Dietary Reference Intakes (DRIs). The panel consisted of physicians, public health professionals and nutritionists from universities in the United States and Canada who reviewed the scientific literature concerning the antioxidant nutrients. They developed dietary reference levels of intake, set Tolerable Upper Intake Levels for the first time, and identified an agenda for further research.
“We reviewed hundreds of scientific documents before arriving at these recommendations,” said Susan T. Mayne, associate professor in chronic disease epidemiology at Yale School of Medicine. “While there has been tremendous interest in the possible value of relatively high intake levels of antioxidant nutrients for preventing a host of chronic diseases, including cardiovascular disease and cancer, one of the key findings from our report is that the scientific evidence does not currently support high intake levels of antioxidant nutrients for chronic disease prevention, other than in research settings.”
The Recommended intake levels of Vitamins C and E were increased and the level for selenium was decreased for men but not for women. The panel also reviewed scientific literature on beta-carotene and other carotenoids, which are naturally-occurring plant pigments that are known to function as antioxidants. The panel did not recommend either a daily intake level or upper limit for these dietary antioxidants.
The report has also set the first limit on daily consumption of selenium and vitamins C and E to reduce the risk of adverse effects from overdose.
Dietary antioxidants are nutrients that help protect cells from a normal — but damaging physiological process known as “oxidative stress.” Such nutrients are a part of the natural makeup of many types of food, particularly fruits and vegetables. They also have been added to some foods and are available in the form of dietary supplements. For years, researchers have sought to understand the role of these antioxidants in reducing the risk of chronic diseases such as cancer, cardiovascular disease, eye diseases and diseases such as Alzheimer’s and Parkinson’s.
The report is the third in a series on dietary recommendations for healthy Americans and Canadians and expands on the Recommended Dietary Allowances (RDAs) that the National Academy of Sciences has set, and on Canada’s Recommended Nutrient Intakes.
The report concludes that more research is needed on the role of dietary antioxidants and carotenoids in the prevention of chronic diseases. More studies are also needed to determine the nutrient needs for children and the elderly; and to examine how selenium, vitamins C and E, and beta-carotene interact with each other and with other food components in human health.
“Most Americans and Canadian adults already get sufficient quantities of vitamins C, E and selenium from their food,” said Mayne. “Healthy people may continue to choose to consume antioxidant nutrient supplements, which is a matter of personal choice, but daily intake levels should not routinely exceed the newly established upper intake levels, including contributions from both diet and supplements.”
Mayne is an associate director of the Yale Comprehensive Cancer Center, for which she leads the Cancer Prevention and Control Research Program. She has directed both observational and intervention studies examining the role of dietary intake or supplemental intake of antioxidant nutrients as it relates to cancer risk. She recently completed a multi-center, randomized clinical trial to determine whether supplemental beta-carotene reduces the incidence of second cancers in patients treated curatively for early stage cancers of the oral cavity, pharynx and larynx.
Mayne also worked with the International Agency for Research on Cancer in Lyon, France, in writing one of its cancer prevention handbooks.
