Date of Award

January 2016

Document Type

Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Yawei Zhang

Abstract

Background: China’s rapid economic and industrial development over the past few decades has been accompanied by tremendous increases in air pollutant emissions and come at a serious cost to the environment and public health. Recent research has revealed an increased risk of adverse birth outcomes associated with perinatal air pollution exposure. Although the mechanisms by which air pollutants contribute to adverse birth outcomes have not yet been established, folate intake has been shown to counteract several of the hypothesized biological pathways.

Hypothesis: Dietary folate intake and folic acid supplementation modify the association between perinatal air pollution exposure (PM10, NO2, SO2) and risk of preterm birth and low birth weight.

Methods: A hospital-based cohort study in Lanzhou, China was conducted between 2010-2012. Demographic information and dietary intake during pregnancy were collected during an in-person interview near the time of delivery, and pregnancy outcomes and complications were abstracted from medical records. All 8,969 participants’ air pollutant exposures throughout pregnancy were calculated utilizing daily PM10, NO2, and SO2 levels from local air monitoring stations and inverse-distance weighting based on both residential and work addresses. Unconditional logistic regression modeling was used to examine the association between perinatal air pollution exposure and adverse birth outcomes and the role of folate as a potential effect modifier.

Results: Mothers exposed to PM10 and SO2 levels above the Chinese NAAQS were at a higher unadjusted risk of adverse birth outcomes than mothers with exposure levels under the standards. Both folate supplementation and high dietary folate intake during pregnancy were significantly protective against both preterm birth and low birth weight without adjustment. Compared to women with air pollutant exposures below the China NAAQS who took folic acid supplements, mothers who did not supplement and had average PM10 and SO2 exposures during pregnancy above the NAAQS were at the highest risk of preterm birth and low birth weight. Women who supplemented with folic acid and were exposed to pollution above the NAAQS had the next highest observed risk, followed by women whose exposures were below the NAAQS but did not supplement.

Similar results were observed for dietary folate intake. Mothers with low dietary folate intake and average PM10 and SO2 exposures above the China NAAQS were at the highest risk of both preterm birth and low birth weight, followed by mothers over the NAAQS with high dietary folate intake, and mothers under the NAAQS with low dietary folate intake. These trends were not observed for NO2. There was no significant interaction between folic acid supplementation or dietary folate intake and any of the air pollutant exposure variables in any of the models.

Conclusion: Our findings support the hypothesis that perinatal exposure to PM10 and SO2 increases the risk of low birth weight and preterm birth. The highest observed risks of adverse birth outcomes were among women highly exposed to PM10 and SO2 with low dietary folate intake and who did not take folic acid supplements. These findings have important public health implications, as birth outcomes like birth weight and gestational age may be indicative of health outcomes later in life, and are relevant for future air pollution policies and standards as well as maternal nutrition recommendations.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 06/07/2018

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