The lead researcher of a recent study showing poorer academic performance among children conceived during the summer says potential parents should be less concerned with watching their calendar and more concerned with watching their drinking water.
Paul Winchester of the Indiana University School of Medicine presented his controversial findings that children conceived between May and August did worse on the Indiana Statewide Testing for Educational Progress during a meeting of the Pediatric Academic Societies May 7. On average, those conceived during the summer did 1 percent worse.
Winchester and his collaborators theorize that the lower performance results from the abundance of pesticides during the summer. In a second study, they showed that birth defects increase among children conceived during that same period.
"It's statistically significant, but you could argue it's not a clinically significant way [of measuring]," said Winchester.
A Weak Link
Allen Wilcox, a senior investigator at the National Institute of Environmental Health Sciences, is one scientist making that argument.
"This is a very weak evidence for a causation," he said. "The best you could say is that it raises the hypothesis, but [it's] a far cry from what should cause a change in behavior."
Wilcox found several weaknesses in the study methods, including the fact that researchers reached their conclusion without any measurements of how much pesticide each individual child was exposed to in utero.
He also criticized the nature of the study. Seasonal studies, he said, are popular because of the relative ease in doing them and the appearance of value.
"On the face of it, it is interesting to lay people, but because it's an easy kind of analysis to do, you are susceptible to false positive results," said Wilcox. "It could be really good. It could be the next great thing. But in general, these kinds of studies haven't held up."
Russell Kirby of the University of Alabama School of Public Health emphasized that a lot more work would be needed before drawing the association between lower academic performance and pesticides. He also pointed out that even a proven association between the two in Indiana wouldn't necessarily apply to the nation, as growing seasons, and therefore pesticide spraying seasons, vary in different regions of the country.
Vincent Garry, a retired pathologist at the University of Minnesota, thinks Winchester might have identified the wrong culprit, having looked at the pesticide component atrazine, which is generally at its peak in the late spring, rather than the insecticides used in June and July, which work by inhibiting neurons in the brain.
He also thinks the jump to pesticides might be a leap, since other factors, like the fact that children conceived during the summer may have to start school at a younger age than their classmates, might have an effect.
Pesticides Perhaps to Blame
But Garry doesn't write off the pesticide theory entirely.
"There's a need to go have a good hard look at it because it could be serious, it could be real, and the first time around, you don't know," he said. "If that happens twice, and someone does it in a little different way and it still comes out, then it's something."
Winchester conceded that many of the criticisms are valid and admitted that his study has not shown enough to make couples reconsider when to procreate.
"To do that would be irresponsible, because we haven't shown that doing that would alter you chances," he said.
But Winchester wanted his study to serve as a wake-up call to people he believes have grown complacent about how the things he studied, such as pesticide use and birth defects, are monitored.
Winchester said he chose to do this study because of mounting evidence that pesticides could have an impact on human reproduction. As he proceeded, he said he saw a lack of monitoring of pesticides in drinking water and the absence of any study of rates of birth defects.
"It's inexcusable that we're not doing measurement of birth defects on some level," he said.
Winchester stated that under current federal laws, water needs only to be monitored four times each year, and suppliers can choose not to send samples to the Environmental Protection Agency in the months when pesticide levels are at their highest.
While she thinks pesticides' effects on children are worthy of research, Stephanie Engel, an epidemiologist at Mount Sinai School of Medicine, remained skeptical of the Winchester's study's conclusions and questioned whether it was worth the media attention it had received.
"There is evidence that pesticides matter," she said, but she stressed that studies in which measurements were taken from pregnant mothers were a much better indicator of what has happened.
Brenda Eskenazi, an epidemiologist at the Berkeley School of Public Health, has run several such studies and found that in utero pesticide exposure could impair the mental development of toddlers but emphasized that "we need to understand measurements better" before reaching broad conclusions.
Despite the preliminary nature of the study, Winchester has no doubts that pesticides are part of the problem.
"This isn't the only cause of birth defects, but it's a large scale, population level defect," he said.
Wilcox remains skeptical.
"If there is a relationship between pesticides and nitrates and development, that would be important," he said. "But this data doesn't give us much to draw those conclusions."