It was Monday's "big" health story, or so we were told. According to CNN.com, there's now an established link between the development of childhood cancers, primarily leukemia and lymphoma, and the use of pesticides.
Sounds scary, maybe even real. But does the science hold up? Maybe, maybe not.
Make that, probably not.
Dr. Chensheng Lu, associate professor of environmental exposure biology at the Harvard T.H. Chan School of Public Health, the lead author of this research, thinks so. But he'd be mistaken. (The full study will be published in the October issue of the journal Pediatrics.)
Lu and colleagues did a meta analysis of a combination of 16 previous studies that examined whether there was a correlation between these cancers and exposure to the chemicals that are found in bug sprays.
Their conclusion? Children who were exposed to insect spray indoors appeared to have about a 45 percent increased risk of developing leukemias and lymphomas. Although while this may sound terrifying if taken at face value, there are many reasons why it should not be taken that way at all. They're all sorts of flaws in the study, some of which are rather obvious.
Let's begin, in no particular order:
- Meta analyses are combinations of a number of previous studies. They are retrospective examined after the fact, rather than prospective where a defined parameter that is determined in advance is measured. Retrospective studies are notoriously unreliable.
- Speaking of notoriously unreliable, the data are self reported which is a very suspect way of collecting information.
- Although a 45 percent increase seems like a substantial number, it is not for retrospective studies. As ACSH advisor and expert biostatistician Dr. Stan Young always says: "In a retrospective study, any effect that is not at least double (100 percent increase) is meaningless."
- There are a number chemicals that are used as insecticides. Many of them are chemically and pharmacologically unrelated to each other. It is a fallacy to assume that any two of these substances will have similar effects upon humans simply because they both kill insects. The study does not attempt to distinguish which insecticides were associated with these cancers, rather, lumps them all together. This will necessarily compromise any conclusions that are derived from the studies.
- Two cancers were studied. A correlation was found (maybe). How many cancers were examined where there was no correlation?
- A similar association was found with the use of herbicides. This is scientifically absurd. The chemicals that are used to kill weeds have nothing whatsoever in common with those that kill bugs, either chemically or mechanistically. This is a huge red flag that suggests that the data are meaningless.
As for CNN.com's Carina Storrs, who relayed the study's conclusions to the public, her work was equally dubious. Here's why:
- She writes: "Other research has suggested a link between parents who are exposed to high levels to pesticides at work, such as through farming, and increased rates of cancers such as leukemia and lymphoma, both in these adults and their children." This is a common bait and switch scare technique. Conflating high exposure, usually from occupational use, with sporadic low exposure is disingenuous and misleading.
- Further, she adds: "Some of the studies that Lu and his colleagues included in their analysis suggest that rates of cancer were highest among children who were exposed in the womb and among those whose parents were exposed before they were conceived." Excuse me? Before you believe that, first ask yourself these questions: How many of the 16 studies examined this? What methods were used to determine this?
- Storrs also used unrelated, heart-tugging anecdotes to support the study's conclusions: "A post-mortem analysis by researchers in Italy of a 7-month-old girl who had died in her sleep revealed high levels of a pesticide called DBNP in the brain tissue." And: "Earlier this month, a Florida family fell ill and a 10-year-old boy was hospitalized after termite fumigation in their home." Now, what does this have to do with cancer? Nothing.
In the end, this study is same old, same old, with some sloppy journalism thrown in to make matters worse. All told, it's a scary headline based on a flawed or inherently limited study, which may or may not have any validity.
What's the end result? It will accomplish nothing other than add to the already-ridiculous fear of chemicals that has already gripped the world.