Lead is prevalent on earth.  It has been known to be toxic to humans as early as 2000 BC. It is in our air, water, and food.  Dioscerides wrote, “Lead makes the mind give way.”^[1]https://www.lead.org.au/history_of_lead_poisoning_in_the_world.htm  Current research finds a positive association between low blood levels of lead and ADHD in children.

Image:  Ana Rodríguez Carrington  Some rights reserved

Health Effects of Lead

Lead causes adverse health effects. These include:

Adults

• Cardiovascular effects, increased blood pressure and incidence of hypertension
• Decreased kidney function
• Reproductive problems (in both men and women)

Children

• Behavior and learning problems
• Lower IQ and Hyperactivity
• Slowed growth
• Hearing Problems
• Anemia

Pregnant women

• Reduced growth of the fetus
• Premature birth^[2]https://www.epa.gov/lead/learn-about-lead#effects

Lead Exposure

Since humans have long known lead was toxic, the first law banning lead use occurred in 1696.  ^[3]https://www.lead.org.au/history_of_lead_poisoning_in_the_world.htm  Starting in the late 1970s, lead was removed from household paint and phased out of gasoline.

According to the US Department of Labor, childhood exposure to lead occurs in our food, air, and water:

In the general population, lead may be present in small but hazardous concentrations in food, water, and air. Lead poisoning from deteriorating old paint is the primary source of elevated blood lead levels in children. Children under the age of six are at risk of developing cognitive health effects even at very low blood lead levels. Pregnant women or those who might become pregnant must avoid lead exposure because it is toxic to the fetus. Another source of environmental exposure to lead is from workers who take home lead dust on their clothing and shoes.^[4]https://www.osha.gov/SLTC/lead/

The positive effects of removing lead from gasoline were found immediately.  Dr. Herbert L. Needlman writes in “HISTORY OF LEAD POISONING IN THE WORLD”, 

The removal of lead from gasoline in 1990, regarded by many as one of the major public health triumphs of the 20th century, had an immediate impact. Between 1976 and 1994, the mean blood lead concentration in children dropped from 13.7 mcg/dL to 3.2 mcg/dL, in direct proportion to the amount of tetraethyl lead produced. One could want no clearer testimony to the efficacy of a well-conceived and consistently applied public health policy.^[5]https://www.lead.org.au/history_of_lead_poisoning_in_the_world.htm

Shockingly, lead is in toys sometimes 29 times the allowable amount!  It’s even in lipstick and cheap jewelry.

The Lead ADHD Connection

Humanity has long recognized lead poisoning’s effect on the mind.   A new study on Mexican children has found a positive association between low levels of lead in the blood and ADHD.

Published in Environmental Health Perspectives, researchers studied 578 Mexican children 6–13 years of age. Specifically, they looked at the ADHD subtypes of hyperactivity, inattention, and their combination in association with lead.^[6]http://ehp.niehs.nih.gov/15-10067/

The US Center for Disease Control identifies the amount of 5 micrograms per decilite as the cut off amount between high and low lead blood levels.  Until 2012, this level was 10 micrograms per decilite.^[7]https://www.cdc.gov/nceh/lead/acclpp/blood_lead_levels.htm  Most noteworthy, the CDC confirms children in Flint, Michigan had blood lead levels above this marker.^[8]http://gawker.com/report-confirms-dangerous-levels-of-lead-in-young-child-1782605361

In the study of Mexican children, only 15% had blood lead levels that exceeded 5 μg/dL.  According to the authors, ADHD symptoms exist at lower lead blood levels in previous studies,

Most published studies with low lead exposure levels (mean blood lead levels ≤ 5 μg/dL) in the past decade have shown that lead is associated with ADHD at levels between 2 to 4 μg/dL measured in whole blood in children between 3 and 17 years (Braun et al. 2006; Cho et al. 2010; Froehlich et al. 2009; Ha et al. 2009; Kim et al. 2010; Nigg et al. 2008, 2010b)^[9]http://ehp.niehs.nih.gov/15-10067/

Conclusively, the Mexican study confirms that ADHD occurs at levels below the CDC cutoff of 5 μg/dL.

Conclusions: In this population of Mexican children, current blood lead level among children with low exposure (≤ 5 μg/dL) was positively associated with hyperactive/impulsive behaviors, but not with inattentiveness. These results add to the existing evidence of lead-associated neurodevelopmental deficits at low levels of exposure.^[10]http://ehp.niehs.nih.gov/15-10067/

Consequently, perhaps it is time for the CDC to lower the threshold again.

Childhood Blood Lead Levels and Symptoms of Attention Deficit Hyperactivity Disorder (ADHD): A Cross-Sectional Study of Mexican Children