The authors emphasize that nutrient supplementation, particularly for certain at-risk populations, has an important place in health care. However, they point out that there is an important difference between observing associations between particular nutrients and health outcomes and detecting causal connections.
"Perhaps no better example exists than the disheartening results of the vitamin E intervention trials for the prevention of cardiovascular disease," says Russell. Lichtenstein explains that although observational studies suggest positive effects, "we lack supporting evidence from intervention trials, and that is critical for making recommendations to the public."
Data are insufficient in other areas as well, according to Lichtenstein. "Disease-nutrient relationships are by their nature very complex. Within the context of high dose nutrient supplementation, outcomes are frequently unexpected. Not only have some studies failed to yield positive results but, occasionally unanticipated negative effects have been observed."
The authors point out that some of the unanticipated findings from high dose single or nutrient cocktails may be because the levels used are much higher than those necessary to prevent deficiency disease. In one study, adding a nutrient antioxidant cocktail to a well established cholesterol-lowering drug treatment actually lessened the beneficial effect. "We still have a lot to learn about the use of high doses of nutrients. The important point is to prevent the cart from getting in front of the horse; we need to validate the science before there is wide scale adoption by the general public as we saw with vitamin E. We can no longer automatically assume there will be no adverse consequences," notes Lichtenstein.
In their overview of the existing literature, Lichtenstein and Russell, both professors at Tufts University's Friedman School of Nutrition Science and Policy and School of Medicine note that their caution is "based on the lack of a complete understanding of nutrient requirements and interactions, and disappointing results of intervention studies with single nutrients or nutrient cocktails."
"The identification, isolation, and purification of nutrients in the early 20th century raised the possibility that optimal health outcomes could be realized through nutrient supplementation," write the authors, but this advance has been "a double-edged sword."
While the current expert opinion is that there is not enough evidence to justify emphasizing nutrient supplements instead of food and diet for maintaining good health, this topic remains under rigorous research, and new data is published regularly. Based on the available information, the authors say, "eat a diet rich in fruits, vegetables, low-fat dairy products, whole grains and fish."
The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University is the only independent school of nutrition in the United States. The School's eight centers, which focus on questions relating to famine, hunger, poverty, and communications, are renowned for the application of scientific research to national and international policy. For more than two decades, the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University has studied the relationship between good nutrition and good health in aging populations. Tufts research scientists work with federal agencies to establish the US Dietary Guidelines, the Dietary Reference Intakes, and other significant public policies.