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Long-term Behavioral and Reproductive Consequences of Embryonic Exposure to Low-dose Toxicants

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The possible societal impact of the decrease in U.S. blood lead levels on adult IQ.

Alan S Kaufman¹, Xiaobin Zhou², Matthew R Reynolds³

¹Yale University School of Medicine, New Haven, CT, USA.

Environmental Research

|May 24, 2014

Summary

Societal decreases in blood lead levels (BLLs) since the 1970s correlate with a 4-5 point increase in American adults' intelligence quotient (IQ). This finding supports predictions of lead exposure

Keywords:

Blood lead levels Cognitive development Intelligence Intelligence quotient (IQ)Neuropsychological assessment

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Published on: May 4, 2020

Area of Science:

Environmental Health
Neuroscience
Public Health

Background:

U.S. blood lead levels (BLLs) have significantly decreased since the 1970s.
The societal impact of declining BLLs on intelligence quotient (IQ) remains largely undocumented.
This study investigates the relationship between decreasing BLLs and mean IQ in American adults.

Purpose of the Study:

To determine if mean IQs of American adults have increased in parallel with societal BLL reduction.
To quantify the association between historical BLLs and current adult IQ scores, adjusted for demographic factors.

Main Methods:

Compared mean IQs of eight adult cohorts (N=800) tested in 2007, with varying mean societal BLLs.
Utilized ANCOVA and correlation analysis, adjusting IQs for education, gender, ethnicity, region, and urban status.
Employed a second adult sample (N=800) tested in 1995 to control for potential confounding by aging.

Main Results:

A significant inverse regression of IQ on BLLs was observed (r=-0.84 to -0.88, p<0.01).
Modeled decreases in BLLs from 20 to 4 μg/dL predicted a 3.8 to 5.2 IQ point increase.
Control analyses confirmed that aging was not a confounding factor in the observed IQ changes.

Conclusions:

Societal reductions in U.S. blood lead levels since the 1970s are associated with a 4-5 point increase in average American IQ.
The observed IQ gains align with previous research predictions regarding lead exposure.
Other contributing factors, such as medical advancements, may also play a role in the documented IQ increases.