News of the Day ... In Perspective04/21/2006
NIH over-hypes connection between air pollution and heart disease, critic says
It is alleged that today’s air pollution, though at a historically low level, nonetheless kills tens of thousands of Americans each year, mainly because of fine particulate matter (PM2.5). A recent mouse study published in JAMA is being used to buttress weak epidemiologic correlations between air pollution level and death rates (JAMA 2005;294:3003-3010). Its publication caused a minor media sensation.
The National Institutes of Health (NIH) issued a press release stating that “test results with laboratory mice show a direct cause-and-effect link between exposure to fine particle air pollution and the development of atherosclerosis.” A summary of the JAMA study is headlined “Particulate air pollution and a high fat diet: a potentially deadly combination.” These results could be used to justify costly tightening of air-quality regulations.
Joel Schwartz, a visiting fellow at the American Enterprise Institute, points out some important features of the study not mentioned by the press. The experimental mice were a genetically engineered strain that has 14 times the normal cholesterol level when fed a high-fat diet. Only one American man in 500 has a cholesterol as high as twice the mean.
Additionally, the mice were exposed to a PM2.5 level of 85 mcg/m3 for the equivalent of 1.560 hours per year, and to filtered air the rest of the time. In contrast, residents of Modesto, Calif., spend only about 80 hours per year at levels that high or higher. While the press release was correct in stating that the average exposure of the mice was at the federal annual standard of 15 mcg/m3, health effects depend on the acute dose as well as the average dose.
Schwartz concludes that the JAMA study shows that “when you take a mouse specially designed to have unrealistically stupendous cholesterol levels, feed it a high-fat diet, and repeatedly expose it to unrealistically high acute levels of PM2.5, that PM2.5 increases the extent of heart disease.” The animals had a 50% increase in the area of atherosclerotic plaques.
“The problem arose when the study’s proponents claimed that this has something to do with the real-world PM2.5 risks faced by human beings.” (TCSdaily.com 4/17/06).