Susan Okie is a former Washington Post medical reporter and science editor, a physician, and a clinical assistant professor of family medicine at Georgetown University School of Medicine.
If you worry about risks to your health from cellphones, genetically modified foods or any of the many threats that pop into the news, reading cancer epidemiologist Geoffrey C. Kabat’s new book may allay some of your fears by putting the headlines in perspective. But reassuring you is not Kabat’s sole mission. He’s also issuing a call to arms, urging his fellow scientists, policymakers and the media to rescue the science of environmental risks from what he presents as its current sorry state. In his view, this important field has fallen victim to low scientific standards, a rush to publish any study that hints at a possible connection between an environmental exposure and a disease, and highly politicized camps of researchers, often too dependent on government funding and media attention to critically examine their findings and do the studies needed to confirm or overturn their theories. “In many cases the resulting versions of the relevant science involve serious simplifications or distortions,” he writes.
It’s far easier for scientists to publish a study that seems to point to a new potential environmental risk than to publish a follow-up that fails to confirm the finding. Readers find news of possible health risks irresistible because — as Kabat points out — it plays into the universal human fear that we’re imperiled by forces beyond our control. Yet those same readers may not hear about other research that tends to refute the initial concerns. Moreover, despite solid evidence that smoking cigarettes, drinking too much, eating an unhealthy diet, being obese and failing to exercise are major environmental causes of illness within our power to change, humans tend to underestimate risks that stem from our behavior and overestimate those that are involuntary, including low-level exposure to substances in the environment.
Such fears may persist even when extensive studies do not confirm a hypothetical link to disease, and even — as in the case of the purported link between childhood vaccines and autism — when investigations find that the study that originally triggered the alarm was fraudulent. Based on the totality of the available science, Kabat concludes, “Vaccines, genetically modified crops and foods, and cell phones are not threats to our well being.”
Through his work at the Albert Einstein College of Medicine in New York, Kabat aims to educate the public about the complicated science of investigating possible environmental hazards, starting with the first principle of epidemiology: “Association doesn’t prove causation.” In other words, simply showing that two things may be connected — for example, that people exposed to a specific chemical seem to show an increased frequency of a particular cancer — doesn’t prove that the first thing causes the second. Detecting an association is only the initial step in an arduous process: It leads to a hypothesis (perhaps the chemical increases cancer risk) that must be tested in carefully designed studies. That might involve identifying a population in whom the disease shows a dramatic increase or one with high levels of exposure to the chemical. Scientists must then consider other factors that might be contributing to or causing the cancer increase, designing experiments to test and perhaps refute their original hypothesis. During this process, which typically takes years of work by multiple teams, researchers need to “question the most basic prevailing assumptions,” seeking sources of error or bias in their thinking.
Kabat writes clearly, but his discussions of association, causality and toxicology are, at times, a bit technical for the general reader. More intriguing — and more unique, in my experience — is his insider’s dissection of the psychology of how environmental studies are funded, reported and interpreted by their authors and by various audiences. As consumers of medical news, we’ve learned that financial support for a study from a drug company or an industry can bias researchers’ interpretation of their results. But Kabat points out that other sources of bias also operate in his field, including scientists’ personal beliefs, political advocacy, eagerness for media attention or desire for continued government funding. He quotes air pollution researcher Robert Phalen, who commented in testimony before the California Air Resources Board, “It benefits us personally to have the public be afraid, even if these risks are trivial.”
Kabat occasionally sounds like a curmudgeon, berating his fellow researchers, the media, even the United Nations and the European Union, both of which have adopted what he considers overly cautious policies that promote the banning of substances suspected of posing a health hazard before there is scientific consensus that they do so. Yet he strongly supports the need for scientists and federal agencies to take potential risks seriously — for example, praising the Food and Drug Administration and the Environmental Protection Agency for funding high-quality research on population-wide exposure to BPA, a chemical found in many consumer products that has been suspected of causing hormone-like effects in animals and humans. Biological support for this theory stems in part from the discovery, several decades ago, that DES, a synthetic version of the hormone estrogen prescribed in the mid-20th century to prevent miscarriages in pregnant women, resulted in cases of a rare vaginal cancer in some of the exposed women’s daughters, as well as other reproductive-tract abnormalities in exposed children of both sexes. However, DES’s potency as a hormone is far greater than BPA’s, and women prescribed the drug were exposed to about 100,000 times the average exposure of Americans to BPA.
Chapters describing how science was deployed in the BPA case and three others make up the most interesting section of the book. Kabat assesses the science on the hypothetical link between cellphones and brain cancer and on the theory that BPA and other environmental chemicals are acting as “endocrine disruptors,” affecting people’s reproductive systems. On both those topics, he concludes that the evidence is reassuring, failing to show that even heavy cellphone use or frequent, low-level exposure to BPA and other hormone-like environmental chemicals causes disease in humans. However, he argues that scientists on opposing sides of these issues continue to interpret the findings according to their own biases, resulting in a lack of consensus. His vivid descriptions of the political advocacy, dueling media campaigns and rival factions in these areas of research make it easy to see why so many people remain worried and uncertain.
After considering issues where science hasn’t put controversies to rest, it’s a relief to read about two cases in which persistent investigators and elegant studies unequivocally nailed down an environmental cause of disease. In one chapter, Kabat recounts the inspiring story of how scientists showed that cervical cancer, the fourth-most-common cancer in women worldwide, is actually a sexually transmitted illness, caused by certain types of the human papilloma virus (HPV) that can infect women during sex. Those discoveries led to the development of HPV vaccines, whose global use may, one day, lead to the eradication of cervical cancer.
In another example, a puzzling cluster of cases of kidney failure among Belgian women treated at a weight-loss clinic suggested that an ingredient in a mixture of Chinese herbs used at the clinic might be involved. The women’s kidneys showed a distinctive pattern of scarring, and some patients also developed early signs of urinary-tract cancer. Years of work by researchers eventually implicated an herb in the genus Aristolochia as the culprit, showing that it contains a toxin that causes mutations in the DNA of urinary-tract cells. According to Kabat, the discovery argues for stricter regulation of herbal products. As pharmacologist Arthur Grollman commented about the toxic herb : “All of the great civilizations have used it. . . . There are certain things that tradition can’t tell you.”
By Geoffrey C. Kabat
Columbia. 248 pp. $35