Low-level Lead and Other Pollutants Causing ADHD
There have been many suspicions about the potential causes of attention-deficit/hyperactivity disorder – also referred to as ADHD. Yet according to the latest research, there is no longer a doubt about the role of lead and other pollutants.
Today, lead and other pollutants are pervading our environment. This is especially the case for many children, because many toys and environments contain significant levels of lead.
Few are surprised about this, because lead has been linked with neurological development problems before. Research has linked lead exposure – to lead paints and other products – to brain development issues and attention issues among children. So what’s the news?
Most of this research related to significant lead exposure to developmental issues. Recent research is finding that even minute levels of lead exposure can cause neurological problems.
And lead isn’t the only low-level heavy metal or pollutant that’s been implicated in ADHD.
Lead exposure in children linked to ADHD in multiple studies
Researchers from South Korea’s Seoul National University College of Medicine recently conducted a study of 1,001 children between 8 and 11 years old. The researchers analyzed the blood of each of the children. They compared this analysis with the student’s IQ scores, ADHD symptoms as given by parents and teachers, along with testing for attention and impulsiveness. This included the Continuous Performance Task test, which measures attention span.
The researchers found that higher levels of lead in the blood are associated with lower IQ levels, higher ADHD scores from teachers and parents and error scores from the attention span testing.
This isn’t the only study that has linked lead and ADHD. In 2013, researchers from the University of Southern Mississippi conducted a meta-analysis and found that among 10,232 children studied, ADHD symptoms were linked with increased lead exposure.
Even low-level lead exposure linked to ADHD
Oregon Health & Science University researchers studied 386 children between 6 and 17 years old: Half of them were diagnosed with ADHD.
After blood analysis, the researchers determined that all of the children had blood levels of lead that were within the safe range defined by the Centers for Disease Control. They also had lead levels consistent with the national average, determined by other research.
The crux arrived when the researchers found that those children with a particular gene variant – HFE C272Y – were most likely to have ADHD.
So what is so special about this gene variant? The HFE is a gene that relates to the regulation of lead use within the body. It regulates lead metabolism.
Other research has found that about 10 percent of the population has this variant. It is not considered particularly dangerous or unhealthy. But having the variant means the body metabolizes lead exposure differently than others.
The researchers found this was the smoking gun they needed: To not simply determine that higher levels of lead are associated with ADHD: That even lower levels are problematic in those healthy children with this gene variant.
And it isn’t as if this is an odd gene variant. As mentioned, one out of ten children will have this variant. And this is seemingly random. So it is perfectly normal to have this gene. The lead exposure is the problem, not the variant. The variant allowed the researchers to pinpoint lead as a cause of ADHD.
Leading researcher Dr. Joel Nigg, a professor at the Oregon Health & Science University medical school, explained how this association leads to the conclusion that lead exposure should now be considered a cause of ADHD:
“Because the C282Y gene helps to control the effects of lead in the body and the mutation was spread randomly in the children, the findings of our study are difficult to explain unless lead is, in fact, part of the cause of ADHD, not just an association.”
Heavy metals exposure and ADHD
Lead is not the only heavy metal to be linked to ADHD.
Mercury exposure has also been associated with ADHD. This was confirmed by research from schools of medicine from Japan’s Wakayama Medical University and Tohoku University. The research analyzed studies prior to 2014 that included thousands of children. Their meta-analysis found environmental mercury exposure increased the risk of ADHD by 60 percent. Mercury exposure also increased the risk of autism by 66 percent.
However, this heightened risk of ADHD was not found with exposure to thimerosal in vaccines. The researchers also investigated thimerosal exposure. They found through meta-analysis that thimerosal exposures did not raise the risk for either ADHD or autism among children.
Why, if mercury is linked to ADHD and autism? Because thimerosal contains a type of mercury called ethylmercury. This is quickly cleared from the body. Thimerosal breaks down into ethylmercury and thiosalicylate, both of which are quickly cleared from the body.
We should also note that thimerosal has been eliminated from childhood vaccines – at least in the U.S – since 2001.
While this is not to say that ethylmercury is a healthy compound, it is nowhere near as toxic as methylmercury. Methylmercury is the bad stuff. This is the stuff found in fish and air pollutants, that can cause serious nerve damage. It is retained in the body and has been linked with various neurological disorders.
In this particular Japanese study, the researchers concluded:
“Moderate adverse effects were observed only between environmental inorganic or organic mercury exposures and ASD/ADHD.”
(This doesn’t mean that thimerosal-containing vaccines – when they were being administered – didn’t increase the risk of ADHD at all. One study did find a slight increased risk of ADHD, but by only about 5 percent. However, most researchers would consider this result non-significant. In comparison, the Japanese study above found no increased risk at all in their international meta-analysis.)
Other heavy metals are also suspected for their link to ADHD. Research from the School of Medicine at Mount Sinai analyzed research between 2009 and 2015 and found that cadmium exposure and manganese exposures in early life are linked with poor cognitive skills among children.
Other pollutants linked with ADHD
We have described 2014 research that has confirmed the link between ADHD and pesticide exposure. Researchers from the University of Michigan tested 989 mothers and their children for pesticide exposure.
The research found those parents and children with higher levels of the paraoxonase-1 enzyme also had greater incidence of ADHD. This enzyme is produced when the body is exposed to certain pesticides.
Sources of exposure and ADHD
The research discussed above relate exposures to not simply the infants. They link exposure to mothers – especially during pregnancy and breastfeeding – to ADHD. Thus, decreasing exposure to pesticides and heavy metals are critical for pregnant mothers who want to reduce the risk of ADHD among their children. Eating organic foods would thus be a start.
Other exposures to consider once the baby is born include polluted air and toys. Polluted city air contains both lead and mercury. This is how many critters, including fish, have become toxic with mercury. Certainly, lead and mercury are also released from industrial outfalls. But these pollutants arising from the burning of fossil fuels will settle into the oceans to be taken up by fish and other critters.
Certainly living in the country or by the seashore is a boon for a child in terms of air pollution. But for those living in the city, there are strategies related to ionizers that help remove heavy metals from the air.
Toys are probably a bigger exposure risk for children. Many children’s toys will contain lead and other heavy metals. Don’t ask me why. You would think that manufacturers would be more careful. But imported toys often lack the safety controls that many Western manufacturers might employ to help prevent heavy metals in toys.
Jewelry is another noted source of lead exposure. Especially costume jewelry. But even serious jewelry worn by adults may contain lead – in clasps, chains and watch bands. Sometimes babies like to put jewelry into their mouths because it is shiny. This can dramatically increase their exposure to lead and other heavy metals.
In 2014, Harvard and Mount Sinai medical school researchers posed a potential solution to this urgent need to help prevent neurotoxic pollution in children:
“To control the pandemic of developmental neurotoxicity, we propose a global prevention strategy. Untested chemicals should not be presumed to be safe to brain development, and chemicals in existing use and all new chemicals must therefore be tested for developmental neurotoxicity. To coordinate these efforts and to accelerate translation of science into prevention, we propose the urgent formation of a new international clearinghouse.”
Hong SB, Im MH, Kim JW, Park EJ, Shin MS, Kim BN, Yoo HJ, Cho IH, Bhang SY, Hong YC, Cho SC. Environmental lead exposure and attention deficit/hyperactivity disorder symptom domains in a community sample of South Korean school-age children. Environ Health Perspect. 2015 Mar;123(3):271-6. doi: 10.1289/ehp.1307420.
Nigg JT, Elmore AL, Natarajan N, Friderici KH, Nikolas MA. Variation in an Iron Metabolism Gene Moderates the Association Between Blood Lead Levels and Attention-Deficit/Hyperactivity Disorder in Children. Psychol Sci. 2015 Dec 28. pii: 0956797615618365.
Goodlad JK, Marcus DK, Fulton JJ. Lead and Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms: a meta-analysis. Clin Psychol Rev. 2013 Apr;33(3):417-25. doi: 10.1016/j.cpr.2013.01.009.
Yoshimasu K, Kiyohara C, Takemura S, Nakai K. A meta-analysis of the evidence on the impact of prenatal and early infancy exposures to mercury on autism and attention deficit/hyperactivity disorder in the childhood. Neurotoxicology. 2014 Sep;44:121-31. doi: 10.1016/j.neuro.2014.06.007.
Geier DA, Hooker BS, Kern JK, King PG, Sykes LK, Geier MR. A dose-response relationship between organic mercury exposure from thimerosal-containing vaccines and neurodevelopmental disorders. Int J Environ Res Public Health. 2014 Sep 5;11(9):9156-70. doi: 10.3390/ijerph110909156.
Sanders AP, Claus Henn B, Wright RO. Perinatal and Childhood Exposure to Cadmium, Manganese, and Metal Mixtures and Effects on Cognition and Behavior: A Review of Recent Literature. Curr Environ Health Rep. 2015 Sep;2(3):284-94. doi: 10.1007/s40572-015-0058-8.
Grandjean P, Landrigan PJ. Neurobehavioural effects of developmental toxicity. Lancet Neurol. 2014 Mar;13(3):330-8. doi: 10.1016/S1474-4422(13)70278-3.