It took exactly 24 hours after spending an entire column dissecting the confusion between correlation and causation (see, “Faith makes you fat,” Aug. 2) to stumble across yet another egregious example of that very fallacy.
This time it was a research study that reported just what everyone involved in the meat and poultry business wants to hear: Children raised on livestock farms are at significantly greater risk of developing leukemia, multiple myeloma and non-Hodgkin's lymphomalater in life.
Researchers from the Centre for Public Health Research at Massey University in Wellington, New Zealandsuggested that exposure to certain viruses during childhood may modify the immune system response and result in a higher risk for blood cancers in adulthood.
Titled, “Farming, growing up on a farm, and haematological cancer mortality,”the studydrewupon data from 114,000 death certificates for people aged 35 and 85 who died between 1998 and 2003 in New Zealand. During that five-year period, more than 3,000 deaths were attributed to blood cancers, with a 22% higher risk of developing cancer found among those who grew up on a livestock farm.Worse, being raised on a poultry farm carried the greatest risk, 22% higher risk of developing. Those who had spent their childhood on poultry farms were three times more likely to develop a blood cancer than others.
The researchers hypothesized that exposure to animal viruses during childhood might be to blame.
So what did the mainstream media make of the study?A typical headline on MSN Health News stated that,“Growing Up Near Livestock Tied to Blood Cancers.”The story went on to trumpet the news that “Children raised on livestock farms are at significantly greater risk of developing blood cancers.”
Understanding the variables
But is that really true? As you might expect, the answer is: Not so fast.
Before anyone goes leaping to any conclusion—implying cause-and-effect—consider some of the study’s limitations. First of all, if the deceased person had a parent who was a poultry farmer, the researchers determined that to mean that the person grew up on a poultry farm. The team found that subjects whose parents were livestock farmers were 22% more likely than those whose parents weren't farmers to develop blood cancer as adults. The finding was especially pronounced among children of poultry farmers, whose blood cancer rate was three times that of their non-farm-kid peers.
But the death certificates provided no information about what type of operation was involved, what sorts of chemicals or hazardous materials might have been used, or even how long the children lived on those farms. Was it a backyard chicken coop? A commercial egg operation? A large-scale growout facility? We don’t have a clue about any of those variables.
Secondly, even if the chicken-cancer connection is in fact solid, it’s still nothing more than a correlation, not causation. And consider this: People who were raised on farms growing crops instead of livestock are less likely to develop blood cancer.
It’s true. Growing evidence, particularly form the reputable Agricultural Health Study conducted in North Carolina and Iowa,indicates that kids raised on crop farms are less prone than non-farm kids to develop asthma, allergies and other conditions affecting the immune system. Medical research suggests that patients suffering from these conditions are actually less likely to develop cancer than non-allergic patients, mainly because allergic conditions seem to enhance the immune system’s ability to detect and eliminate malignant cells.
Not only that, but massive epidemiological data show that farmers overall are less likely than the urban population to die of heart disease and lung or coloncancer, three of the leading causes of death in the United States.
So far from being a death sentence, growing up on a farm—even a livestock operation—is not only a background to be proud of, it might even keep you kicking longer than the city folks who know neither the hardships nor the joys of being part of the most fundamental profession in all of the human experience.
And until someone comes up with proof, the chickens-cause-cancer hypothesis remains just that: Pure speculation about a correlation that may prove in the end to have nothing to do with the birds themselves.
› For more on the New Zealand study, log ontowww.ncbi.nlm.nih.gov/pubmed/21795741.
Dan Murphy is a veteran food-industry journalist and commentator