This study explored exposure to greenness and proximity to large green spaces, such as parks, and effect on birth outcomes including birth weight and gestational age and evaluated whether this association depended on socioeconomic status (SES; as measured by mothers' education level). The study included over 8,000 births from Barcelona, Spain during 2001-2005.The study examined greenness within 100m around the mother's place of residence (using Normalized Difference Vegetation Index) and proximity to major green spaces within 500m from a mother's residence. The study used these two factors to attempt to separate the effect of greenness on physical activity (which is associated with park use) compared to potential effect of air pollution or stress (the impact of which is decreased by greenness immediately surrounding the home).
The study found that for mothers from the lowest SES, living near major green spaces led to increased birth weight of their children. However, there was no effect for other SES levels and no overall effect when SES was not considered in the analysis. These results suggest that SES may mediate the effect of greenness on birth weight. In addition, there was also no association between greenness near the home residence and either birth weight or gestational age, which prevented the authors from separating the effects of physical activity from other mechanisms. Future studies would benefit from measuring levels of physical activity directly. Though this is one of the first studies of the association of greenness and birth outcome, the importance of SES in this relationship is consistent with other literature suggesting that income-related health disparities are less prominent with higher degrees of exposure to greenness.
In their discussion the authors suggest that living near a major green space may impact women of low SES more because women of higher SES tend to have increased mobility and therefore can more easily visit further away green spaces. However, more research will need to be done to see if this finding holds and to understand what might be driving the difference in strength of relationship between exposure to greenness and birthweight dependent on SES. The authors recommend future studies use direct measures of physical activity and stress levels to detect underlying mechanisms and improved measures of SES to confirm the importance of SES in the relationship of greenness and birth outcomes.
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