The possible societal impact of the decrease in U.S. blood lead levels on adult IQ.
BACKGROUND
The dramatic decrease in U.S. blood lead levels (BLLs) since the 1970s has been documented--however, the anticipated societal impact on intelligence quotient (IQ) has not. The objectives of this study were to determine whether mean IQs of American adults, adjusted for demographics, have increased in concert with society's decreasing BLL.


METHODS
Mean IQs of eight normal adult cohorts (N=800), tested individually in 2007 by trained clinicians, were compared using ANCOVA and correlation analysis. Cohorts ranged in mean societal BLLs from 4 1/2 μg/dL (born 1985-1987) to 19 μg/dL (born 1963-1972). IQs were adjusted for confounders-education, gender, ethnicity, region, urban status. To control for age, we analyzed IQ data for a second adult sample (N=800), tested in 1995-all born when BLLs were high (1951-1975, BLL ≥ 15 μg/dL).


RESULTS
When controlling for education, gender, ethnicity, and region, the regression of IQs on BLLs was significant (r=-0.84, p<0.01); the modeled change in BLLs from 20 to 4 μg/dL suggests predicted increases of 3.8 IQ points (95% CI, 1.4-6.2). Also controlling for urban status produced significance (r=-0.88, p<0.01) with predicted increases of 5.2 points (95% CI, 2.4-8.0). Control analyses ruled out aging as a confounder.


CONCLUSIONS
The dramatic societal decreases in BLLs in the U.S. since the 1970s were associated with a 4-5-point increase in the mean IQs of Americans. This effect is consistent with researchers' predictions; however, other variables (e.g., medical advances) may have contributed to the IQ gains.
Yale University School of Medicine, New Haven, CT, USA. Electronic address: alanskaufman@gmail.com.
Alan S
AS
Kaufman
Curriculum Associates, Boston, MA, USA. Electronic address: xiaobin@gmail.com.
Xiaobin
X
Zhou
University of Kansas, Lawrence, KS, USA. Electronic address: mrreynolds@ku.edu.
Matthew R
MR
Reynolds
Yale University School of Medicine, New Haven, CT, USA. Electronic address: nadeenk@gmail.com.
Nadeen L
NL
Kaufman
California State University-San Bernardino, San Bernardino, CA, USA. Electronic address: garo@garogreen.com.
Garo P
GP
Green
Pearson Clinical Assessment, San Antonio, TX, USA. Electronic address: Larry.Weiss@Pearson.com.
Lawrence G
LG
Weiss
D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007360:Intelligence / Q000187:drug effects*; D007361:Intelligence Tests; D007854:Lead / Q000009:adverse effects* / Q000097:blood; D008297:Male; D014481:United States; D055815:Young Adult
D007854:Lead
Blood lead levels; Cognitive development; Intelligence; Intelligence quotient (IQ); Neuropsychological assessment