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. 2019 Sep:176:108505.
doi: 10.1016/j.envres.2019.05.036. Epub 2019 May 24.

Prenatal air pollution and childhood IQ: Preliminary evidence of effect modification by folate

Christine T Loftus  1 , Marnie F Hazlehurst  2 , Adam A Szpiro  3 , Yu Ni  2 , Frances A Tylavsky  4 , Nicole R Bush  5 , Sheela Sathyanarayana  6 , Kecia N Carroll  7 , Catherine J Karr  8 , Kaja Z LeWinn  9
Affiliations

Prenatal air pollution and childhood IQ: Preliminary evidence of effect modification by folate

Christine T Loftus et al. Environ Res. 2019 Sep.

Abstract

Objectives: Animal studies suggest that air pollution is neurotoxic to a developing fetus, but evidence in humans is limited. We tested the hypothesis that higher air pollution is associated with lower child IQ and that effects vary by maternal and child characteristics, including prenatal nutrition.

Methods: We used prospective data collected from the Conditions Affecting Neurocognitive Development and Learning in Early Childhood study. Outdoor pollutant exposure during pregnancy was predicted at geocoded home addresses using a validated national universal kriging model that combines ground-based monitoring data with an extensive database of land-use covariates. Distance to nearest major roadway was also used as a proxy for traffic-related pollution. Our primary outcome was full-scale IQ measured at age 4-6. In regression models, we adjusted for multiple determinants of child neurodevelopment and assessed interactions between air pollutants and child sex, race, socioeconomic status, reported nutrition, and maternal plasma folate in second trimester.

Results: In our analytic sample (N = 1005) full-scale IQ averaged 2.5 points (95% CI: 0.1, 4.8) lower per 5 μg/m3 higher prenatal PM10, while no associations with nitrogen dioxide or road proximity were observed. Associations between PM10 and IQ were modified by maternal plasma folate (pinteraction = 0.07). In the lowest folate quartile, IQ decreased 6.8 points (95% CI: 1.4, 12.3) per 5-unit increase in PM10; no associations were observed in higher quartiles.

Conclusions: Our findings strengthen evidence that air pollution impairs fetal neurodevelopment and suggest a potentially important role of maternal folate in modifying these effects.

Keywords: Air pollution; Neurodevelopment; Particulate matter; Pediatric health; Prenatal folate.

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Conflict of interest statement

Conflict of interest: The authors report no conflicts of interest relevant to this article.

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1. Inclusion Flowchart
Of N=1503 mothers enrolled in CANDLE, up to N=1005 were included in analyses. Outcome (IQ) was not available for children who did a phone visit only or who were uncooperative or otherwise unable to complete the assessment. Geocodes were not available if mothers opted out of sharing of identifiable information. (a) Model 1 (minimal) adjusted for child age and sex, and date of birth (b) Model 2 (main) additionally adjusted for maternal education, insurance status, Childhood Opportunity Index subscales, maternal age, race, and IQ, prenatal depression, prenatal smoking, birth order, breastfeeding, and child sleep. (c) Model 3 (expanded) additionally adjusted for prenatal vitamin use, marital status, paternal education, maternal pre-pregnancy body mass index, and Knowledge of Infant Development survey score.
Figure 2
Figure 2. Prenatal Air Pollution and Full-scale IQ at Outcome Assessment
Associations between prenatal air pollution and child full-scale IQ. For NO2 or PM10, effect estimates are adjusted for covariates (see footnotes) and scaled to a 5 unit increase in pollutant. Near roadway is defined as residence within 150 meters of a busy roadway. (a) Associations adjusted for child age and sex, date of birth, maternal education, insurance status, Childhood Opportunity Index subscales, maternal age, race, and IQ, prenatal depression, prenatal smoking, birth order, breastfeeding, and child sleep. Abbreviations: NO2 = nitrogen dioxide; PM10 = particulate matter of 10 microns or less in aerodynamic diameter; CI = confidence interval
Figure 3
Figure 3. Associations Prenatal Air Pollution and Full-scale IQ by Child and Maternal Characteristics
Strata-specific associations between prenatal air pollution and child full-scale IQ. All associations adjusted for the main model covariates (see footnote). P-values for interaction were estimated using a Wald test with robust standard errors.
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