On Washing your Fruit: ADHD and Pesticides

May 24 2010 Published by under Behavioral Neuro, Neuroscience

Sci was a little startled recently when she saw "the latest study" on ADHD splashed across the frontpage of Yahoo. You can see it here on Reuters.

(Run for the hills, indeed. Or maybe run AWAY from the hills, since they might have pesticides)
However, the story broke a good TWO DAYS in advance of the paper actually coming out, and so Sci was forced to possess her soul in patience until she had access.
But she's got it now! And let's take a look at this thing.
But first, I want us to all breathe in together and say: "Correlation is not causation"
Say it with me: "Correlation is not causation"

(Behold Sci contemplating the science of the universe)
All right, here we go.
ResearchBlogging.org Bouchard, et al. "Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides" Pediatrics, 2010.

We all know that there are a lot of pesticides used in the US today. And some people believe that attention deficit/hyperactivity disorder (ADHD) is on the rise. Sci isn't so sure about this one herself. ADHD that meets diagnostic criteria is VERY easy to find. I'm not saying that ADHD doesn't exist, of course it does. The question is whether or not there's an increase because there's an increase, whether we're seeing an increase because we are looking for it (and people certainly are), or whether we're seeing an increase because it's seen as a very easy and good thing to treat for the sanity of the parents and teacher (the child might be hyperactive, and certainly can be treated with Ritalin, but is the child ADHD? Often, yes, but not always). But certainly the DIAGNOSES of ADHD are on the rise. And of course people are looking for a cause.
Pesticides aren't necessarily the first thing you'd look at, but they aren't the last thing either. Most of the time, when people look at studies with pesticides and humans, they look at people exposed to high doses of pesticides, rather than the lower daily doses that most Americans are exposed to. And high doses of pesticides have been linked with changes in brain development in children. So actually, it's not that big of a leap to hypothesize that lower levels of pesticides might cause smaller changes in brain development, like those associated with ADHD.
So for this study, the authors surveyed a total of almost 4000 children, or rather, they did an analysis of data collected from the National Health and Nutrition Examination Survey. Of those, they managed to grab a little over 1000 of them (boys and girls) and get a urine sample, which they tested for metabolites associated with pesticides. They then called up the parents, and ran a questionnaire by them which contained questions to diagnose ADHD via the DSM IV. They then checked the urinary metabolite levels against the questionnaire results for the child.
What they got was all in table form and unpleasing to the eye, but has some important stuff in it. They found that

There was a 55% to 72% increase in the
odds of ADHD for a 10-fold increase in
DMAP concentration, depending on the
criteria used for case identification.

Basically, of the kids that had urinary metabolites of pesticides that were detectable (not all were detectable, in fact it appears that for some of the metabolites, levels were below detection limit about half the time), it appears that the incidence of ADHD correlated with an increased level of organophosphates in the urine. This means that the more pesticides you had in your urine, the more likely you were to have ADHD. They controlled for age and socio-economic status.
And of course everyone in the media read this study and started freaking out about how you should feed your kids only organic fruit.
Hold your horses, please.
The authors themselves admit that this is a correlation, not a causation. It's a good correlation, and they did a great job with controls for things like economic class, race, etc, (well done!) but it is NOT causation. And it raises far more questions than it answers. Here are a few Sci can think of off the top of her head:
1) Is it the pesticides in the CHILDREN, or could it be exposure to pesticides in utero? Could it be exposure over one period of the lifespan?
2) What was the ADHD status of the parents of each of the children who came out positive? Is there a genetic correlation to account for some of this?
3) Did they ask the parents WHAT they fed their kids? Did they ask the children WITHOUT any pesticide metabolites in their urine if THEY had ADHD? Why didn't they? The study only covers children with measurable metabolites. What if there is a difference? What if there ISN'T?
4) Does taking Ritalin (a bunch of the kids were on Ritalin) change the concentration of pesticides in the urine? Possibly not, but if both chemicals are metabolized similarly there could be issues there.
So as you can see, there are way more questions than there are answers. As to the organic fruit? Sci says meh. Washing your fruit well is ALWAYS a good idea and should always be done, but if this is something in neural development, and your kid already has ADHD, washing the fruit now is VERY unlikely to help. Organic fruit may help, but pesticides spread.
And let's not run for the hills just yet. There are still many things to be accounted for, including genetics (which may play a VERY big role), environment, timing of exposure (if pesticides are the cause), and a huge control (kids with undetectable metabolites) that they missed. Not only that, Sci thinks they could have used a control group of kids fed mostly organic food and done a comparison. It would surprise me if someone has it planned. I would also like to see an animal study with human-comparable levels of pesticide exposure on neural development over the lifespan (start with fetal exposure, go up to exposure through mother's milk, etc., and behaviorally test for deficits later. Not a hard study to do, actually...)
In the meantime wash your fruit (you should already be washing your fruit). Buy organic if it makes you feel better. But don't run for the hills just yet, the science isn't done. It's a nice correlation, but it isn't causation yet.
Bouchard, M., Bellinger, D., Wright, R., & Weisskopf, M. (2010). Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides PEDIATRICS DOI: 10.1542/peds.2009-3058
EDIT: Reader Alex pointed out that there are some points that Sci missed. They DID look at undetectable levels of pesticides, and they DID look at kids treated with Ritalin. But I still think we can't say much until we can show a group of kids without pesticide exposure at all (or extremely minimal). I also would love a really long longitudinal study of women and their diets in utero through the kids growing up, as I'll bet many of the big changes would be in utero or during nursing.

10 responses so far

  • Snarkyxanf says:

    I'm sure pesticides are associated with hyperactivity.
    Caffeine and nicotine both count as pesticides, right? They kill bugs anyway...

  • FiSH says:

    Yet another good reason to avoid Yahoo. This is a very good example about how poorly science is communicated to the general public (which unfortunately includes politicians and other responsible individuals in government). It is so typical for a reporter to grab one sound bite, rather than going for substance: "Pesticides tied to ADHD" sounds so much better than "Increased levels of organic phosphates are found in the urine of kids that might potentially be diagnosed with ADHD, which may or may not have a causal role in the disorder, and might in fact be a consequence of the disorder, but we don't really know yet."

  • Gina Pera says:

    Finally, we do know the genetic factor is 76% with ADHD. Some parents with untreated ADHD might be less-than-cautious in using these many organophosphate products and thus limiting their child's exposure (or their own exposure).
    Gina Pera, author
    Is It You, Me, or Adult A.D.D.?

  • Gina Pera says:

    Oh heck, only the last part of my post came through last time.
    There are many reasons why ADHD is being diagnosed more now. I know you did not mean to provide an exhaustive list, but neither did you need to add stigma and an "anti-science" tone by suggesting that children are being treated medically for the benefit of parents and teachers. That's pretty shameful in a "science" blog.
    Yes, there are many other factors to consider. One is that preliminary study indicates that people with ADHD are deficient in some key minerals, including calcium and magnesium -- coincidentally the "good minerals" that compete with the "bad minerals" such as mercury and also organophosphates.
    Given that mineral deficiency is epidemic among women of child-bearing age in this country, this is an important line of inquiry. Not only will the fetus be deprived of critical building blocks for the neurological system but it will also be exposed to added risk from omnipresent organophosphates and toxic metals.
    So, are the organophosphates causative (not out of the question, given their development as neurotoxins) or associative? There is the mineral question. And there is also the fact that most of these children most likely have a parent with untreated ADHD (76 percent heritability) who is perhaps not as careful as they should be with regard to chemical exposure in the home (flea bombs, pet products, other home-garden pesticides).
    This study is only a small first step, in my opinion. The status of the parents' organophosphate load, their own ADHD, and the parent/child's nutritional status are important factors.
    Gina Pera, author
    Is It You, Me, or Adult A.D.D.?

  • chris says:

    As a teacher, I can definitively say that there are many children who are diagnosed with ADHD and medicated simply for the convenience of parents and teachers. I have, in my ten years of teaching, encountered only 2 children who I believe were truly ADHD and in need of medication. Every other child was impulsive/fidgety/inattentive largely due to lack of discipline (note that discipline does not equal punishment), lack of outlets for natural childhood energy, and lack of good study habits. I strive to get children OFF medication when possible, and most of my children are off meds and well behaved (at school and at home) by the end of the school year and earning excellent marks. I have taught K-5 and each year have 4-6 kids on meds. I am not a psychologist, but my undergraduate degree is in psychology so have some decent background there to seriously question the validity of these diagnosis.

  • Alex says:

    I don't understand why you are interpreting the study so cautiously. As you yourself say, there is ample evidence linking organophosphates with brain development abnormalities in children. For many parents, that is already enough evidence to minimize pesticide exposure of their children. This study is a good observational study that is consistent with other research in the area. Next steps would more definitively nail down the role of organophosphates (and the pathogenesis of ADHD), but this study is good evidence that there is a role for organophosphates. As for your questions:
    1. A fair question, to the extent that prior or in utero organophosphates is correlated with current organophosphates, which are completely eliminated from the body in 3-6 days. If true, this would argue for a stronger, not weaker, causal effect of organophosphates, albeit for a specific time in the development of the child.
    2. Also a fair question, though it is unlikely that any genetic effect would explain the association seen in this study. To do so, you would have to postulate that affected parents are more likely to feed their kids foods with higher organophosphates than unaffected parents. I think that is a stretch.
    3. The study clearly includes children with and without metabolites.
    4. The study includes analyses excluding children on methylphenidate (Ritalin), which still showed the association on organophosphates with ADHD.
    The authors provide a detailed discussion of the limitations of their study in the discussion section of their paper. Worth a second read, and perhaps an addendum to your blog to bring up some of their points, also valid.

  • Scicurious says:

    Alex: I'm interpreting the study so cautiously because, although it's a good correlation, I'm not going to call it until there's a proven link. And it's quite clear that it's not JUST pesticides at play here, but environmental factors acting on something else (like the strong possible role of genetics). You raise some good points though.
    As far as the genetic effect, it wouldn't explain the association, but it could provide a genetics/environment interaction.
    You're right, I missed that they included the kids with low metabolites. There's a major issue with the children with no detectable metabolites if they ARE included as well. WHY did they have no detectable metabolites? In addition, none of these children were assessed for diet, and I think that's pretty important.
    They did a good job stating the limitations of their study, but I do think they could have included that they didn't check for diet and whether certain parents were trying to keep pesticides out, and how that related. There also need to be careful studies of when the organophosphate exposure happens, which they couldn't do in this study.
    But looking back, I realize some stuff I missed, so I will edit.

  • Gina Pera says:

    Chris, I'm sure you mean well, but your statements betray a huge gap in your knowledge of ADHD. A dangerous gap.
    It is not your place to "strive to get children OFF" medication. It is your job to teach children and, when the child has ADHD and accommodations, to follow them.
    And no, I'm sorry, but having an undergrad degree in psychology gives you no expertise whatsoever in playing psychiatrist or psychologist with these children.
    I suggest you learn more about the topic before you inject your bias into such situations.

  • Gina Pera says:

    Alex wrote: "To do so, you would have to postulate that affected parents are more likely to feed their kids foods with higher organophosphates than unaffected parents. I think that is a stretch."
    Why do you think that is a stretch?
    I do not mean to paint parents with undiagnosed/untreated ADHD in a bad light. Many, I'm sure, are extremely cautious about the exposure their children have to household chemicals and the like. But you have to know that households affected by ADHD are often chaotic, and that means meals are often not well thought out. There might be higher consumption of fast food, for example, or frozen foods, which might have higher pesticide residues.
    I need to read the study, to see why only pesticides from non-organic foods are talked about in these reports and other organophosphates are completely ignored (such as pet products, household/garden pesticides, etc.)

  • Alex says:

    Just to be clear, organophosphates would be an example of an environmental factor, as opposed to genetic factors. I agree that a genetic environmental interaction is possible. I don't think anyone is suggesting that organophosphates are THE cause of ADHD. But given this and other studies, it is hard to argue that organophosphates play NO role in ADHD. As a parent, I would restrict exposure of my children to foods with organophosphates until it is proven to be safe, rather than wait until some study proves it to be causative.
    I do believe that the measured urinary metabolites come from all ingested sources, not just non-organic food.
    Gina, you paint a plausible scenario, but I am not aware of any scientific evidence that supports your hypothesis that ADHD parents expose their kids to more organophosphates than unaffected parents, so I would consider it an unlikely interpretation of the data. Lots of households are chaotic, not just those affected by ADHD. And chaotic or not, many parents are not aware of which foods contain organophosphates or what potential dangers they may have.