In his “Explainer” column at Slate yesterday, Brian Palmer raised alarm about grilled and smoked meats, suggesting that by eating them we may be, as the headline puts it, “Cooking Up Cancer”:
A growing body of research suggests that cooking meats over a flame is linked to cancer. Combusting wood, gas, or charcoal emits chemicals known as polycyclic aromatic hydrocarbons. Exposure to these so-called PAHs is known to cause skin, liver, stomach, and several other types of cancer in lab animals. Epidemiological studies link occupational exposure to PAHs to cancer in humans. When PAHs from a flame mingle with nitrogen, say from a slab of meat, they can form nitrated PAHs, or NPAHs. NPAHs are even more carcinogenic than PAHs in laboratory experiments. The reasonable conclusion is that grilling meat may be hazardous to your health.
The evidence linking cancer to cooking meat over a combustion source has been accumulating for decades. Epidemiologists first noticed a connection between the consumption of smoked foods and stomach cancer in the 1960s. Japan, Russia, and Eastern Europe, where smoking is a popular way to preserve meat and fish, became laboratories for gastric cancer research. Newer studies suggest that eating smoked meats may lead to cancer even outside the gastrointestinal tract. A 2012 study, for example, linked smoked meat consumption with breast cancer.
Palmer then compares current attitudes toward grilled meats to outdated acceptance of tobacco use:
In the mid- to late-19th century, doctors determined that lip and tongue cancer rates were higher among smokers of pipes and cigars. Despite this link, major medical journals mocked those who opposed smoking. The Lancet, the leading journal of the time and still one of the most important medical journals in the world, wrote in 1879, “We have no sympathy with prejudices against … tobacco, used under proper restriction as to the time and amount of the consumption. … A cigar when the mood and the circumstances are propitious [is] not only to be tolerated, but approved.” Moderation, not abstinence, was the order of the day.
It wasn’t until 1964 that the Report of the Surgeon General finally and firmly declared that smoking was indisputably linked to the surge in lung cancer. By that time, epidemiologists had a complete picture of the long-term effects of the increase in cigarette smoking that began around the time of World War I. The conclusions practically drew themselves. Still, it took the public health community decades to agree that smoking in moderation is a terrible idea.
I learned of the article from my friend Jeff Woodhead on Twitter, who took Palmer to task for sensationalizing the dangers of grilling and noted that habitual cigarette use carries far greater risks than exposure to charred meat. I don’t disagree. However I want to defend Palmer on one point. He is actually correct to compare grilling meats to smoking tobacco, though not in the way he realizes.
That pack-a-day consumption of cigarettes greatly elevates one’s risk of lung cancer is no longer disputed by any sensible person. Moderate use of other forms of tobacco, in contrast, carries much less danger. The Lancet article that Palmer mocks for suggesting that moderation in tobacco use is nothing to worry about overstates the case but was not too far from the truth.
Just how dangerous is it to enjoy an occasional cigar “when the mood and the circumstances are propitious?” A study in Preventive Medicine compared rates of lung cancer among smokers of various kinds of tobacco to those of non-smokers. Cigarette smokers were 16 times more likely than never smokers to get lung cancer. Smokers of cigars only, pipes only, and cigars and pipes all fared much better. Further, lung cancer among pipe and cigar smokers was concentrated among those who were the heaviest consumers. “Among pipe and/or cigar smokers only, patients with lung cancer were more likely than controls to have been long-time smokers of 5 or more cigars or 5 or more pipefuls per day and to have inhaled. The odds ratio for those smoking 5 to 9 cigars or pipes per day was 3.2 and for those smoking 10 or more units 6.7. The odds ratio of those cigar or pipe smokers who inhaled was 12.3.”
A cohort study published in The New England Journal of Medicine followed about 17,000 men enrolled in Kaiser Permanente health plans who reported never smoking pipes or cigarettes. Over a course of more than 20 years, the study compared health outcomes for non-smokers and smokers of cigars. Cigar smokers carried a relative risk of cancer in the aerodigestive tract of 2.02 and in the lungs of 2.14.
A third study in BMJ examined the risks of dying from three smoking-related diseases among former cigarette smokers who had switched to smoking pipes or cigars. Their mortality risk relative to users of pipes and cigars who were never cigarette smokers was 1.51. To put that in perspective, their relative risk compared to people who had never smoked at all was 1.68. In other words, the study found that even former cigarette smokers who switch to pipes and cigars lowered their mortality risk to a level not much above that of never smokers.
Brad Rodu, an advocate of harm reduction approaches in tobacco control, summarizes many of these risks. What it basically comes do is this: Cigarettes are uniquely dangerous because they are inhaled directly into the lungs and are very addictive. Other forms of tobacco that are mainly enjoyed in the mouth and lend themselves less easily to habitual consumption are significantly less dangerous. The risks are real, but much, much lower than those associated with cigarettes.
How does all of this compare to eating meat? Palmer doesn’t cite many sources that specify the dangers, but one study he links to does associate consumption of smoked meat with breast cancer. It finds an adjusted odds ratio of 2.31-3.13. If that’s accurate (and it may be on the high side), then eating lots of grilled meat may actually be a lot like enjoying an occasional cigar — which is to say that it’s a reasonable choice many adults may decide to make.
(Note: Some of the studies cited in this post use relative risk while others use odds ratios. These are not identical measures but should be roughly comparable.)
It’s also interesting to ask how this compares to the dangers of exposure to secondhand tobacco smoke. Smoking bans have proliferated on the justification that workers should not be put at risk. Whatever one’s opinion of these policies, consider the findings from the landmark 2006 report from the Surgeon General. The report concludes without equivocation that environmental tobacco smoke increases the risk of lung cancer in non-smokers. By how much? The reports’ table of meta-analyses of studies estimates relative risks of exposure at home for non-smoking spouses or at work for non-smoking employees in a range of 1.12 at the low end to 1.43 on the high end. Those are low relative risks! If they are enough to justify comprehensive bans on indoor smoking — not to mention the outdooor bans that are now so popular — then one may well question the ethics of allowing restaurant cooks to expose themselves to grill smoke on our behalf.
One of the big problems with reporting on cancer is that it focuses on the wrong question. Journalists ask, “Does X increase the risk of cancer?” The answer is very often yes, but they don’t follow-up with, “By how much?” Lifestyle choices carry trade-offs and better reporting would help readers put them into perspective. Palmer, to his credit, does write that the “risk-reward equation for smoking differs from that of grilling or frying meat” and acknowledges that the epidemiology on the latter is not yet clearly established. His mistake is to carelessly lump all forms of tobacco use into one, ignoring the fact that different types and different use patterns carry substantially different levels of risk.
Of course, few yet advocate completely giving up grilled or smoked meat, much less passing legislation to restrict it. “Everything in moderation,” said one of the toxicologists quoted in the Slate article. One assumes that the toxicologist’s definition of “everything” doesn’t include tobacco, because who would say that these days? But Palmer’s comparison of grilling to smoking isn’t crazy. It just tells us a lot more about contemporary bias against tobacco use than it does about the dangers of meat.