May 09, 2007
Pesticides Make Dumber Summer-Conceived Babies?
Do babies conceived during summer perform worse at cognitive tasks?
INDIANAPOLIS — Does the time of year in which a child is conceived influence future academic achievement? Yes, according to research by neonatologist Paul Winchester, M.D., Indiana University School of Medicine professor of clinical pediatrics. Dr. Winchester, who studied 1,667,391 Indiana students, presents his finding on May 7 at the Pediatric Academic Societies' annual meeting.
Dr. Winchester and colleagues linked the scores of the students in grades 3 through 10 who took the Indiana Statewide Testing for Educational Progress (ISTEP) examination with the month in which each student had been conceived. The researchers found that ISTEP scores for math and language were distinctly seasonal with the lowest scores received by children who had been conceived in June through August.
Why might children conceived in June through August have the lowest ISTEP scores? "The fetal brain begins developing soon after conception. The pesticides we use to control pests in fields and our homes and the nitrates we use to fertilize crops and even our lawns are at their highest level in the summer," said Dr. Winchester, who also directs Newborn Intensive Care Services at St. Francis Hospital in Indianapolis.
"Exposure to pesticides and nitrates can alter the hormonal milieu of the pregnant mother and the developing fetal brain," said Dr. Winchester. "While our findings do not represent absolute proof that pesticides and nitrates contribute to lower ISTEP scores, they strongly support such a hypothesis."
I can think of many other potential explanations. For example, maybe the babies conceived in the summer do not get enough vitamin D in the winter and this lack of vitamin D causes their brains to develop poorly when their brains are developing most rapidly. Maybe nutritional status matters more during later months of pregnancy.
Pesticides might also be upping the rate of premature births.
INDIANAPOLIS — The growing premature birth rate in the United States appears to be strongly associated with increased use of pesticides and nitrates, according to work conducted by Paul Winchester, M.D., professor of clinical pediatrics at the Indiana University School of Medicine. He reports his findings May 7 at the Pediatric Academic Societies' annual meeting, a combined gathering of the American Pediatric Society, the Society for Pediatric Research, the Ambulatory Pediatric Association and the American Academy of Pediatrics.
Dr. Winchester and colleagues found that preterm birth rates peaked when pesticides and nitrates measurements in surface water were highest (April-July) and were lowest when nitrates and pesticides were lowest (Aug.-Sept.).
A repeat of this experiment in other regions could control for the pesticide effect since not all areas of the United States have much agriculture. Also, growing season start dates and lengths differ by region. The effect of pesticides would start later and end earlier in Maine than in Missouri for example. We could also see a difference depending on the source of water supply. Water supplies probably vary considerably in their pesticide concentrations.
I'd like to see the numbers on the growing premature birth rate. Is it related to medical advances that allow more premature babies to survive? What are the mortality numbers when plotted against the birth rate.
Seems like this research is designed to support a preconceived notion, and not the other way around.
What poppycock! Talk about a leap of logic. This is not "evidence" that pesticides and nitrates do anything at all. For all we know at this point the differences in clothing a kid wears based on season changes the amount of stimulation and hence the amount of development. (Correlation is not causation. The import rate of bananas is what, 0.97?, relative to diabetes incidence. Bananas don't cause diabetes.)
All this is evidence of is that there is a seasonal variation in test performance scores. Randall's speculations are just as valid as the author's are on this one. And more likely!
Plus I want to know just what the spectrum of testing score difference is. I remember once reading about how one blood pressue pill had given significant results relative to another. Only to find that the difference between the two meds was under 2mm of mercury. Yeah, statistically significant -- of no use in real life clinically.
As to pre-term birth, the differential between the rates is a meager 1.12% or about 10% relative to the rates (prematu max vs min 11.91% v 10.79%). In other words, by their own basic data, the "environmental impact" doesn't affect 9 out 10 women.
Never mind that the good doctor is ignorant of basic physiology or he wouldn't be blaming nitrates. Nitrates simply fix nitogen in plants and to the extent that they get into the food they are almost 100% neutralized in the liver in first pass effect. So nitrates simply cannot be causal of anything. (Assuming you aren't eating hot dogs 3x a day for months on end). All this nitrate malarky started because babies in the midwest got toxic doses of nitrates from local well drinking water resulting in methemoglobinemia (blue-baby syndrome) and because in vitro studies (where guess what -- there's no liver!) showed n-nitroso-amines to be potent carcinogens. Most recent epidemiologic study to date cannot find any evidence that these compounds actually kill humans:
1: Nutr Rev. 1998 Apr;56(4 Pt 1):95-105. Links
Dietary nitrates, nitrites, and N-nitroso compounds and cancer risk: a review of the epidemiologic evidence.
* Eichholzer M, * Gutzwiller F.
Institute of Social and Preventive Medicine, University of Zurich, Switzerland.
Experimental animal studies have shown N-nitroso compounds (NOC) to be potent carcinogens. Epidemiologic evidence of the carcinogenic potential of dietary NOC and precursor nitrates and nitrites in humans remains inconclusive with regard to the risk of stomach, brain, esophageal, and nasopharyngeal cancers. Inadequate available data could obscure a small to moderate effect of NOC.
PMID: 9584494 [PubMed - indexed for MEDLINE]
Doctors with computers, and no idea about statistics or their use. The article could just as easily have offered the correlation as proof of the scientific basis of astrology, and it would have been just as truthful.
Which is why I use physicists and not statisticians or (gasp!) other doctors to vet my work.
I find statisticians get too involved with the numbers and over-manipulate them.
The physicists typically want answers and the difference in attitude makes all the difference.
Hmmm, I'm skeptical of these findings as well. It occurs to me that children conceived in the summer months will be born the following spring. That would make them less than 5 ½ years old when they are old enough to attend school which starts in the fall. I wonder if this would effect the studies results?
Do they control for parental characteristics? Teenagers probably have much more unprotected sex in the summer, because they don't have anything else to do.
[i]Do they control for parental characteristics? Teenagers probably have much more unprotected sex in the summer, because they don't have anything else to do. "[/i]
That's the first thing I thought when I read that.
My first wild-ass guess was that mothers of babies born in the spring had just been through the cold and flu season. Could a mother's infection influence their babies?
The time at which a baby gets conceived certainly will influence total pathogen exposure during fetal development and also when during fetal development the pathogen exposure happens. There are likely more important stages of forebrain development when pathogen exposure will matter more.
The same holds for nutrition. A baby conceived in June will experience lower vitamin D levels during the late months of pregnancy. Though maternal vitamin supplements are probably pretty common.