Children who eat more than 12 hot dogs per month have nine times the normal risk of developing childhood leukemia, a USC epidemiologist has reported in a cancer research journal. Two other reports in the same issue of Cancer Causes and Control suggest that children born to mothers who eat at least one hot dog per week during pregnancy have double the normal risk of developing brain tumors, as do children whose fathers ate hot dogs before conception.
The recent findings, which are generating a great deal of controversy and concern, could help explain why the incidence of childhood leukemia and brain tumors has been increasing over the last two decades, say the researchers, led by USC epidemiologist John Peters.
The scientists caution that the studies are preliminary and based on relatively small numbers of cases--a total of 621 cancer victims in the three studies and an equal number of controls. They also note that the statistical association is not necessarily a cause-and-effect relationship.
Critics, as well as the researchers themselves, point out that such studies are difficult to conduct and interpret because people have a hard time recalling what they have eaten.
Nonetheless, the scientists argue that the results are significant and the issue deserves much more intensive scrutiny. In response to the findings, researchers at the University of Minnesota have modified their National Cancer Institute-sponsored study on childhood leukemia to explore the possible connection to hot dogs.
The researchers suggest that the trigger for the cancers might be the nitrites used to preserve processed meats such as hot dogs. Nitrites are converted in the body to highly carcinogenic nitrosamines.
Still, none of the investigators argue that people should stop eating hot dogs based on the findings.
Because of the low incidence of these childhood tumors, "this is not a hazard at the level of tobacco smoke or high-fat diets," said epidemiologist David Savitz of the University of North Carolina, author of one of the studies on pregnant women. "The rational response would be a small modification of your consumption."
"It's an intriguing idea because hot dogs certainly contain chemicals that one might wonder about," said Dr. Clark Heath, vice president for medical research of the American Cancer Society. "I don't think they prove the case," he said, but the results are feasible because animal studies have established that nitrites cause cancer. "Obviously, it is an idea that will need to be explored further."
Researchers from the hot dog and cured meat industries were not available for comment Thursday. A spokeswoman for the National Cancer Institute could not provide anyone familiar with the findings.
Other researchers scoffed at the findings as an example of the "carcinogen of the week" syndrome. "The problem is that there are an enormous number of variables in a study like this," said nutrition expert Michael Pariza of the University of Wisconsin. "You don't know whether they were undernourished, for example, or if they had adequate exercise. . . . It would be extremely premature to draw any conclusion from this type of study."
Other researchers also attacked the studies because they were published in a journal that is not peer-reviewed, meaning that experts did not have a chance to critique the results before they appeared in print.
Leukemia and brain tumors have been a concern to pediatric oncologists because they have been increasing more than twice as fast as childhood cancer overall. In the 17 years that such data has been collected, Heath said, cancer among children up to age 14 has increased by an average of 0.8% per year, while acute lymphoblastic leukemia has increased 1.7% per year--a 27.4% total over that period. Brain tumors have increased 1.8% per year over the same period, a 32.8% total. The cause of the increases has been a mystery.
Even so, the cancers are still considered very rare. Acute lymphoblastic leukemia strikes only about three in every 10,000 children, so even a ninefold increase still amounts to a relatively small risk.
The researchers said they did not set out to indict hot dogs. Peters and Savitz have been key players in the studies examining the link between electromagnetic fields (EMFs) and childhood tumors. As part of those studies, they decided to explore other potential causes. "Our idea was to test as many hypotheses about possible causes as we could think of," Peters said.
The finding about hot dogs "was a real surprise," he added. "It was the biggest risk for anything we saw in the study--about four times the risk for EMFs."
Peters and his colleagues identified 232 children under age 10 in the Los Angeles area who developed leukemia between 1980 and 1987 and a comparable number of matched children who did not develop it. The parents answered extensive questions about lifestyle, parental occupations, exposure to potential carcinogens and diet for the children and themselves.
In particular, they were questioned about consumption of cured meats, including hot dogs, bologna, bacon, sausage and ham--all of which contain nitrites--as well as charcoal-broiled meats, which contain other carcinogens.
They found no link to any food other than hot dogs. In addition to the findings for the children, Peters found that the risk of leukemia in children whose fathers consumed hot dogs regularly before the children were conceived was 11 times normal. He did not distinguish among various types of hot dogs because all contain nitrites.
Savitz and Greta R. Bunin of Children's Hospital in Philadelphia performed similar studies among children with leukemia and brain tumors. Savitz studied 234 cancer cases and 234 controls in Denver; Bunin studied 155 cancer cases and 155 controls in Philadelphia. Both found about twice the normal risk of brain tumors among children whose mothers consumed hot dogs weekly during pregnancy.
Savitz also found a doubled risk of leukemia among children who ate at least one grilled hamburger per week and a doubled risk of brain cancer among those who ate at least one hot dog per week. All the researchers found that the greatest risk was among children who did not take vitamins--implying that vitamins may have some type of protective effect.
Although the researchers suspect nitrites in the cured meats, they agree that it could be something else as well--perhaps the high fat content of hot dogs, bacteria or some other chemical in them. Or it could be that a high hot dog intake "is simply a marker for a very bad diet," Bunin said.
The fact that the studies were not designed with hot dogs as a primary concern means that there are many unanswered questions, Savitz said.
"This was not by modern standards a sophisticated study of diet and cancer. We know how to do better, but hot dogs just weren't a prominent enough issue to devote extensive parts of the questionnaire to them."
But, he concluded, "now they are."