December 3, 2012
Study Casts Doubt On Research Linking Foods With Cancer Risk
redOrbit Staff & Wire Reports - Your Universe Online
Many of the studies claiming to link certain types of food with an increased or decreased risk of cancer provide "weak" or only "nominally significant" statistical evidence to support their claims, according to new research.
As part of the study, which has been published in the American Journal of Clinical Nutrition, Jonathan Schoenfeld of the Harvard School of Public Health and John Ioannidis of Stanford University identified 50 of the ingredients most commonly used in recipes contained in one prominent cookbook, Sarah Kliff of the Washington Post wrote on Friday.
Forty of those ingredients, including salt, pepper, flour, egg, bread, tomato, onion, milk, bacon, mushrooms, sugar, wine, nuts, tea and raisins, had been the subject of at least one study which linked to either an increased risk or a decreased risk of cancer, Kliff added. Thirty-nine percent were associated with an increased risk, 33-percent with a decreased risk, and 23-percent had no clear evidence either way, according to the researchers.
"The vast majority of those studies, Schoenfeld and Ioannidis found, showed really weak associations between the ingredient at hand and cancer risk," the Washington Post writer explained. "A full 80 percent of the studies had shown statistical relationships that were 'weak or nominally significant,' as measured by the study´s P-values. Seventy-five percent of the studies purporting to show a higher cancer risk fell into this category, as did 76 percent of those showing a lower cancer risk."
"I was constantly amazed at how often claims about associations of specific foods with cancer were made, so I wanted to examine systematically the phenomenon,” Ioannidis told Kliff via email. "I suspected that much of this literature must be wrong. What we see is that almost everything is claimed to be associated with cancer, and a large portion of these claims seem to be wrong indeed."
While Schoenfeld's and Ioannidis' work does not immediately discount the possibility of those products, or others, improving or worsening the odds that a person's risk of developing cancer, it does suggest that much of the research "linking foodstuffs to cancer revealed no valid medical pattern at all," McKie said.
"We found that, if we took one individual study that finds a link with cancer, it was very often difficult to repeat that in other studies," Schoenfeld told The Observer. "People need to know whether a study linking a food to cancer risk is backed up before jumping to conclusions."