Alan S Kaufman1, Xiaobin Zhou2, Matthew R Reynolds3, Nadeen L Kaufman4, Garo P Green5, Lawrence G Weiss6. 1. Yale University School of Medicine, New Haven, CT, USA. Electronic address: alanskaufman@gmail.com. 2. Curriculum Associates, Boston, MA, USA. Electronic address: xiaobin@gmail.com. 3. University of Kansas, Lawrence, KS, USA. Electronic address: mrreynolds@ku.edu. 4. Yale University School of Medicine, New Haven, CT, USA. Electronic address: nadeenk@gmail.com. 5. California State University-San Bernardino, San Bernardino, CA, USA. Electronic address: garo@garogreen.com. 6. Pearson Clinical Assessment, San Antonio, TX, USA. Electronic address: Larry.Weiss@Pearson.com.
Abstract
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.
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.
Authors: Ibrahim Sani Shabanda; Isa Baba Koki; Kah Hin Low; Sharifuddin Md Zain; Sook Mei Khor; Nor Kartini Abu Bakar Journal: Environ Sci Pollut Res Int Date: 2019-11-20 Impact factor: 4.223
Authors: Kristine K Dennis; Elizabeth Marder; David M Balshaw; Yuxia Cui; Michael A Lynes; Gary J Patti; Stephen M Rappaport; Daniel T Shaughnessy; Martine Vrijheid; Dana Boyd Barr Journal: Environ Health Perspect Date: 2016-07-06 Impact factor: 9.031