Thursday, April 28, 2011

Sugar and Cellphones: On Scientific Challenges

Many people consider the knowledge claims generated by natural scientists to be, for the most part, quite sound. Leucippus may have speculated that atoms compose all matter, but only through the work of a slew of modern scientists—Lavoisier, Dalton, Thompson, and many others—can most of us say, with almost perfect certainly, that we know atoms compose all matter. Of course, the frontiers of science continue to challenge our assumptions about the natural world and our ability to use the scientific method to understand it—but for the most part, most people trust the scientific method and consider the knowledge it has generated quite sound.

Against this backdrop of certainty, the New York Times Magazine published two feature articles earlier this month which, despite their apparently disparate topics, offered fascinating commentary on the complexities—practical, statistical, and political—of the scientific method. The first, Do Cellphones Cause Brain Cancer?, discusses, not surprisingly, the role that cell phones may play in causing brain cancer. On its face, the article demands attention, as the ideas the author presents should be of interest to any cell phone user worldwide. But I found the article's treatment of the scientific method just as intriguing.

The author of the article, Dr. Siddhartha Mukherjee, details three ways that cancer epidemiologists can determine the cause of a particular cancer. "The first," he writes, "is arguably the simplest. When a rare form of cancer is associated with a rare exposure, the link between the risk and the cancer stands out starkly." As an example, he notes that doctors in London discovered, in the late Eighteenth Century, a remarkably high incidence of scrotal cancer among chimney sweeps. He notes that the second way is more challenging: "The opposite phenomenon occurs when a common exposure is associated with a common form of cancer: the association, rather than popping out, disappears into the background, like white noise." The common exposure-common cancer epidemiology problem baffled researchers during the Twentieth Century who could not prove a statistical link between smoking and lung cancer.

The third way that epidemiologists can determine the cause of cancer presents more difficultly still. "A common exposure... associated with a rare form of cancer," Mukherjee writes, "is cancer epidemiology’s toughest conundrum." He goes on:
The rarity of the cancer provokes a desperate and often corrosive search for a cause... And when patients with brain tumors happen to share a common exposure—in this case, cellphones—the line between cause and coincidence begins to blur. The association does not stand out nor does it disappear into statistical white noise. Instead, it remains suspended, like some sort of peculiar optical illusion that is blurry to some and all too clear to others.
Mukherjee devotes the remainder of the article to discussing the challenges scientists face in determining what is (and isn't) a carcinogen. He doesn't provide the reader with a simple response to the question he asks in the title, but he does explain why the scientific method, ever considered tried-and-true, may not provide a pathway for answering the question anytime soon. Appropriately, he ends the piece thus: "Understanding the rigor, labor, evidence and time required to identify a real carcinogen is the first step to understanding what does and does not cause cancer."

The second article, Is Sugar Toxic?, discusses the growing body of nutrition science that suggests that sugar—the sugar we find in small white packets, the high-fructose corn syrup we find in many packaged foods, and the sugar we find in fruit—is toxic to our bodies. Written by Gary Taubes, the author of Why We Get Fat: And What to Do About It, the article focuses on the work of Robert Lustig, a pediatrician made famous by a lecture he delivered in 2009, the video of which has been viewed more than one million times. I encountered a link to the video on a friend's Facebook wall about a week before I read the Times' article. 

Lustig has dedicated his career to demonstrating that sugar is toxic, that it is the leading cause of obesity and cancer. He makes a convincing argument, and while some scientists have bought it, others have not. Not surprisingly, the Sugar Association and the Corn Refiners Association have weighed in, declaring sugar safe and using evidence from the Food and Drug Administration to bolster their claim.

Although the question of sugar's toxicity is important, Taubes' discussion of the challenge that science has faced in attempting to determine the safety of sugar is equally important. Tabues details a powerful argument from Walter Glinsmann, a former F.D.A. administrator and current adviser to the Corn Refiners Association. Glinsmann contends that "sugar and high-fructose corn syrup might be toxic, as Lustig argues, but so might any substance if it’s consumed in ways or in quantities that are unnatural for humans."  Tabues rightfully asks, "at what dose does a substance go from being harmless to harmful? How much do we have to consume before this happens?"

Lustig counters this argument by noting that sugar is not an "acute toxin," one similar to others the F.D.A. regulates, those with effects that "can be studied over the course of days or months." Sugar and high-fructose corn syrup, he claims, are “chronic toxins." Lustig explains that they are “not toxic after one meal, but after 1,000 meals.” This, according to Taubes, is the great challenge facing Lustig and others who wish to prove that sugar is the cause of many common ailments.

In a way, the challenge faced by Lustig is similar to the challenge faced by cancer epidemiologists when they sought to establish a causal relationship between smoking and lung cancer. Many Americans eat excessive amounts of sugar, and many Americans have chronic diseases related to obesity. There appears to be, at the minimum, a correlation between sugar consumption and obesity. But can science prove a causal link between the two? The scientific method doesn't provide an easy way to establish one. Taubes and Mukherjee help us understand why.

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