Lead Exposure Causes ADHD

Lead Exposure Today

With the discovery of the lead contamination crisis in Flint, Michigan, lead poisoning has recently caught American’s attention. The corrosive water from the Flint River caused lead from old pipes to leach into the water supply. Up to 12,000 children have been exposed to dangerous levels of lead. Five percent of children in Flint have elevated blood lead levels1. There is no safe blood lead level in children. Unfortunately, Flint is not an isolated incident. Other cities, even within Michigan, have a higher prevalence of lead poisoning than Flint. In 2014 20% of children on the west side of Detroit had high lead exposure. Low academic test scores within the Detroit Public School system have been linked to these high lead levels1.

In addition to being exposed through water from lead pipes, children can be exposed to lead from lead-based paints. Lead-based paints were not banned until 1978. Thus all homes built before 1978 are likely to contain some lead-based paint. About 24 million homes contain deteriorated leaded paint. When old paint peels, homes can have high levels of lead-contaminated dust2. Children are especially at risk of lead poisoning in these environments because they are likely to put their contaminated hands or toys in their mouth2.

In the past, leaded gasoline was a huge source of lead exposure. Strong relationships between leaded gasoline and blood lead levels were found in at least 14 countries3. Lead began to be phased out of gasoline in the 1970’s. Interestingly, the decline of leaded gasoline may be responsible for the huge drop in crime that American cities experienced since the 1990’s.

Lead Exposure Increases Crime Rate

Exposure to lead around preschool age has been associated with aggressive and criminal behavior in adolescence and acts of violent crime later in life. A strong association between child blood lead levels and later crime rates has been found in in The United States, Great Britain, Canada, France, Australia, Finland, Italy, Germany, and New Zealand3. One study found that areas of a country with a lot of lead in the air (mainly from industrial emissions) had murder rates during 1989-1991 that were four times higher than areas with low lead in the air3. This pattern most likely occurred because the people who were children during the 1970’s accumulated lead in their bodies at that time. When they reached their early 20’s, the serious side effects of lead presented as abnormal behavioral3.

Research done at the city level has uncovered the same pattern. When lead in the air in major U.S. cities (from vehicle emissions) increased, the crime rate increased 22 years later. The relationship was so strong that researchers were able to conclude that for every one metric ton of lead released 22 years earlier, aggravated assaults increased 59 times4. The lead in gasoline during 1941-1975 explained 90% of the variation in violent crime in America in 1964-19983. The 13% decrease in aggravated assault rates in 2010 could have been due to the complete phase-out of leaded gasoline in 19864.

Lead’s Effect on the Brain

Exposure to lead during childhood causes a range of adverse effects on the developing brain including behavioral problems, impulsivity, inattention, impaired learning and IQ2,3. A national survey of children aged 8-15 found high blood lead concentrations were associated with ADHD. Children with the highest blood lead levels were over twice as likely to have ADHD as children with the lowest blood lead levels5. A study conducted a few years earlier on an even larger group of children aged 4-15 found children with the highest blood lead levels were over four times as likely to have ADHD as children with the lowest blood lead levels6. A 2016 study uncovered a causal link between lead exposure and ADHD symptoms, particularly hyperactivity and impulsivity, in children with a mutation of a gene that regulates lead in the body. The researchers concluded, “The findings of our study are difficult to explain unless lead is, in fact, part of the cause of ADHD, not just an association7.”

Treatment Exists

Fortunately lead poisoning can be treated. Standard treatment is called chelation therapy. A child is given a medicine either by mouth, by muscle injection, or by IV infusion. The medicine binds to lead in the blood and the brain. Then the medicine along with the lead is excreted in urine. This therapy reduces the body’s lead levels in just a few days.

The best way to avoid lead poisoning is to avoid exposure to lead in the first place. Parents can help protect their children by washing their hands, toys, and play areas often with soap and water. Most children who have lead poisoning do not look or act sick so it important to have children’s blood lead levels tested by a pediatrician2.

 

 

References.

  1. Wilkinson, M. (2016). Kids’ lead levels high in many Michigan cities. The Detroit News. Retrieved from www.detroitnews.com/story/news/michigan/flint-water-crisis/2016/01/27/many-michigan-cities-higher-lead-levels-flint/79438144
  2. Centers for Disease Control and Prevention (CDC). (2016). Lead. U.S. Department of Health & Human Services. Retrieved from www.cdc.gov/nceh/lead
  3. Nevin, R. (2007). Understanding international crime trends: The legacy of preschool lead exposure. Environmental Research, 104(3), 315-336.
  4. Mielke, H. W., & Zahran, S. (2012). The urban rise and fall of air lead (Pb) and the latent surge and retreat of societal violence. Environment International, 43, 48-55.
  5. Froehlich, T. E., Lanphear, B. P., Auinger, P., Hornung, R., Epstein, J. N., Braun, J., & Kahn, R. S. (2009). Association of tobacco and lead exposures with attention-deficit/hyperactivity disorder. Pediatrics, 124(6), e1054-e1063.
  6. Braun, J., Kahn, R., Froehlich, T., Auinger, P., & Lanphear, B. (2006). Exposures to Environmental Toxicants and Attention Deficit Hyperactivity Disorder in U.S. Children. Environmental Health Perspectives, 114(12), 1904.
  7. Nigg, J., Natarajan, N., Elmore, A., Friderici, K., & Nikolas, M. ). (2016). Variation in an Iron Metabolism Gene Moderates the Association Between Blood Lead Levels and Attention-Deficit/Hyperactivity Disorder in Children. Psychological Science, 27(2), 257-269.

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