Recent weeks have offered a rich harvest of new "health" threats with splashy headlines warning us about the supposed dangers from processed meats, hair dyes, and tanning parlors.
While all of these stories are all a little odd, perhaps the oddest is the one about how meat increases the risk of stomach cancer. This story was featured on the networks and in several major papers. One news outlet even went so far as to tell its readers just how much bacon they could eat before being at risk for cancer!
What makes the meat and stomach cancer story odd from the get-go is the fact that compared to the rest of the world, North America has one of the lowest rates of stomach cancer incidence and mortality in the world at 10 per 100,000. The highest rates are found in Latin America, Asia and Eastern Europe. And the pattern of declining incidence found here is repeated throughout much of the Western world.
But the really peculiar thing about the meat and stomach cancer scare is how fundamentally at odds the news reports were from the actual science.
Back in the Spring the Journal of National Cancer Institute in the United States published a study on meat intake and the risk of stomach and esophageal cancer by a research team led by Carlos Gonzalez of the Catalan Institute of Oncology in Barcelona, "Meat Intake and Risk of Stomach and Esophageal Adenocarcinoma Within the European Prospective Into Cancer and Nutrition". The researchers looked at cancer and nutrition involving some 520,000 Europeans for over six years. According to Gonzalez, there was an increased risk of stomach cancer associated with total meat intake, red meat intake and processed meat consumption. But a mere 330 subjects developed stomach cancer, and in those most at risk of developing it -- those over 60 -- the absolute risk of developing it over 10 years was 0.33% for the heaviest meat eaters groups versus 0.26% for the near vegetarian crowd. Where's the epidemic, and the big difference?
But then came another study, "Processed Meat Consumption and Stomach Cancer Risk: A Meta-Analysis," by Susanna Larsson from the Karolinska Institute in Stockholm. Larsson conducted a meta-analysis of 15 previous studies on the relationship between processed meat consumption -- including bacon, sausage, hot dogs, salami, ham and various smoked meats -- and stomach cancer risk that were published between 1966 and 2006. She found that "increased consumption of processed meat is associated with an increased risk of stomach cancer."
The world media dutifully reported this frightening news, scaring people off their BLTs and sausage at breakfast, and no doubt saving many a pig's life.
Only the conclusion was compromised.
To start, only seven of the 19 studies included in the study had results that were statistically significant. Of the seven studies linking bacon and stomach cancer -- the headline grabber -- only two were statistically significant; while of the nine regarding sausage only three had statistical significance. And to top it off, Larsson's own study of processed meat and cancer, which she included in the meta-analysis, showed no statistically increased risk of stomach cancer associated with eating bacon, sausage and hot dogs, and ham and salami.
The studies that were statistically significant reported relative risks that were so small as to be indistinguishable from chance. For example, the relative risks for stomach cancer from an increase in processed meat consumption of 30g a day was 1.38, where relative risks below 2 are considered not to indicate a causal connection. Even eating ham, which had the highest reported risk, had a relative risk of only 1.64.
Meanwhile, contradicting Larsson's metaanalysis was an enormous prospective study, "A Prospective Study of Diet and Stomach Cancer Mortality in United States Men and Women" in 2001 done by the American Cancer Society. It involved 436,000 Americans and found no increased risk of stomach cancer associated with eating processed meats. That study, during 14 years of follow-up, documented 439 stomach cancer deaths in women and 910 in men. It found that: "none of the food groups examined were associated with risk of stomach cancer except for an unexpected increased risk with vegetable consumption in women."
Why hasn't anyone warned women not to eat their veggies? It would have been ridiculous, of course, just as it is now to exaggerate dangers from processed meat.
All of this highlights a major flaw in the way in which the media covers food and health stories that was pointed out recently by the International Food Information Council's Food for Thought, a report on how the media reports on food issues.
According to the IFIC, there were more than 3,000 assertions of harm or benefit of some food based on a scientific study in news stories in 11 leading North American newspapers in 2005. Yet only 2% mentioned whether the study found a statistically significant connection between something like the food and the disease. In other words, whether the connection was real or not was never reported in the overwhelming majority of the stories.
With reporting like that, we can be assured of a continued run of headlines warning that bacon causes stomach cancer and ... whatever. Let the pigs rejoice.
John Luik is a writing a book about health policy.