New findings on lead and learning: SAT, mental retardation trends linked to lead levels

Two years ago, economist Rick Nevin reported that long-term, worldwide trends in crime levels consistently correlated with changes in environmental levels of lead (see related article, Crime Times, 2007, Vol. 13, No. 3). Now, research by Nevin links dropping lead levels in the United States to rising scores on the Scholastic Aptitude Test (SAT) and declines in the prevalence of mental retardation.

Using statistics from multiple national databases, Nevin found that “1936–1990 preschool blood lead trends explain 65% of the 1948–2001 variation in U.S.A. mental retardation (MR) prevalence, 45% of the 1953–2003 variation in the average scholastic achievement test (SAT) verbal score, and 65% of the 1953–2003 variation in the average SAT math score.” Drops in preschool blood levels correlated with drops in mental retardation 12 years later and increases in SAT scores 17 years later. The findings, Nevin says, “are consistent with lead-induced cognitive damage in the first year of life. “

In analyzing his data, Nevin controlled for the increasing number of students taking SAT prep courses and for changes in the number of students speaking a foreign language at home, both of which can affect SAT scores.

Nevin also concludes that “SAT and MR trends by race are consistent with racial differences in how 1960s slum clearance affected childhood exposure to severe lead paint hazards.” He notes, “SAT trends by Hispanic origin are consistent with an especially sharp fall in preschool blood lead in New York City since 1970.”

Noting that even small elevations in lead levels are linked to significant drops in IQ, Nevin says his findings lend urgency to the task of reducing preschool lead exposure. Currently, leaded paint in older houses is the primary source of U.S. children’s exposure to toxic levels of lead.

“Trends in preschool lead exposure, mental retardation, and scholastic achievement: Association or causation?” Rick Nevin, Environmental Research, January 22, 2009 (epub prior to print publication). Address: Rick Nevin, ricknevin@verizon.net.