Soaking Up the Sun: The Role of Sunshine in the Production of Infant Health

Abstract

This research explores the role of sunshine in birth outcomes production, focusing primarily on fetal growth. The most obvious mechanism is through vitamin D absorption, which could explain racial disparities in birth weight because skin pigmentation inhibits this process. However, sunshine may have additional effects and is closely connected to environmental factors, season of birth, and geography. Combining daily weather data with 1989–2004 birth outcomes from the Natality Detail Files, we estimate sunshine's effects in a range of models that disentangle these confounding factors. Our results suggest that sunshine has a positive but diminishing effect on birth weight for blacks and a negative effect for whites. These findings are consistent with the presumed positive but diminishing effects of sunshine via vitamin D balanced against the possible negative effects via folic acid depletion and immune system impairment. The estimated magnitudes are in line with those found for other key factors such as feeding programs and air pollution and suggest that sunshine's effects explain a nontrivial portion of racial differences in birth weight. Implications include possible interventions (vitamin supplementation for blacks, sun avoidance for whites) and the need to include sunshine as a potentially important factor in birth outcomes research.