Environmental quality can be considered a direct input into health, with infant health responding to maternal exposure to pollution while in utero as well as post-birth. Isolating a causal relationship between pollution and health is challenging for many reasons. First, measurement error in pollution levels attenuates coefficients and makes a relationship difficult to detect. Second, there are numerous pollutants, many of which are measured infrequently or not at all. Lastly, a number of confounding variables must be ruled out in order to interpret a relationship between environmental quality and health as causal. For example, families may sort into areas of varying pollution levels based on socioeconomic characteristics or business cycles may have an independent effect on both pollution levels and health. Furthermore, the relationship between health and pollution may be nonlinear, meaning that reductions in pollution below a given level may not improve health.
Researchers have exclusively relied on quasi-experimental designs such as policy changes or temporal variation in pollution levels to assess the impact of environment on infant health. The introduction of the Clean Air Act of 1970 reduced infant deaths in the most polluted counties. Similarly, infant mortality declined more in counties with greater reductions in total suspended particulates during the 1981–82 recession. The introduction of the EZPass toll system in the Northeastern USA reduced traffic and thus pollution levels near the freeway, subsequently increasing birth weight and reducing prematurity for newborns near the freeway. The Chernobyl fallout over Sweden did not detectably affect infant health; however, students that were in utero during the fallout experienced deficiencies in human capital as evidenced by lower test scores and high school graduation rates.
From both a theoretical and empirical perspective, there has been an increasing focus on the importance of in utero and early life conditions on later health and outcomes. Theoretical models emphasize the timing of investments. If investments are substitutable across periods, then disadvantage early in life can be overcome by later life investments. However, early investment is important if skills acquired during early periods can help beget skills in later periods. This article highlights several mechanisms through which transmission of health may occur – initial endowments, environmental influences, parental abilities, and investments. Researchers have relied heavily on quasi-experimental strategies such as policy changes, natural disasters, and sibling studies to identify a causal relationship between early life influences and health. This is an emerging and growing literature.
- Heckman, J. (2007). The technology and neuroscience of capacity formation. Proceedings of the National Academy of Sciences (PNAS) 104(33), 13250–13255.
- Sexton, M. and Hebel, J. R. (1984). A clinical trial of change in maternal smoking and its effect on birth weight. The Journal of the American Medical Association 251(7), 911–915.
- Almond, D. and Currie, J. (2011). Human capital development before age five. In Ashenfelter, O. and Card, D. (eds.) Handbook of labor economics, vol 4B, pp. 1315–1486. Amsterdam: Elsevier.
- Almond, D. and Currie, J. (2011). Killing me softly: The fetal origins hypothesis. Journal of Economic Perspectives 25(3), 153–172.
- Barker, D. (2004). The developmental origins of adult disease. Journal of the American College of Nutrition 23(supplement 6), 588S–595S.
- Currie, J. (2009). Healthy, wealthy, and wise: Socioeconomic status, poor health in childhood, and human capital development. Journal of Economic Literature 47(1), 87–122.
- Currie J. (2011). Inequality at birth: Some causes and consequences. National Bureau of Economic Research Working Paper No. 16798. Cambridge, MA: National Bureau of Economic Research.
- https://www.barkeradoptionfoundation.org/ The Barker Adoption Foundation.