Impact of individual and neighborhood social capital on the physical and mental health of pregnant women: the Japan Environment and Children's Study (JECS).

BACKGROUND: Previous studies revealed positive, negative, and no influence of social capital on the health outcomes of pregnant women. It was considered that such differences were caused by the disparities of outcome measures and sample sizes between studies. Our chief aim was to verify the positive influence of social capital on the health condition of pregnant women using established health outcome measures and large-scale nationwide survey data. METHODS: We employed questionnaire survey data from 79,210 respondents to the Japan Environment and Children's Study, and physical and mental component summary scores from the 8-Item Short-Form Health Survey as outcome measures. We estimated the effect of individual and neighborhood social capitals on physical and mental component summary scores. To consider the property that the richness of social capital would be generally determined by individual characteristics, and to estimate the causal influence of social capital on health without bias caused by said property, we adopted average treatment effect estimation with inverse probability weighting. Generally, average treatment effects are based on the difference of average outcomes between treated and untreated groups in an intervention. In this research, we reckoned individuals' different levels of social capital as a kind of non-randomized treatment for respective individuals, and we applied average treatment effect estimation. The analysis regarded pregnant women with the lowest level of social capital as untreated samples and women with other levels of social capitals as treated samples. RESULTS: For mental component summary score, the maximum average treatment effects in the comparison between the lowest and highest levels of social capital were approximately 4.4 and 1.6 for individual and neighborhood social capital, respectively. The average treatment effects for the physical component summary score were negligible for both social capital types. CONCLUSIONS: Social capital particularly contributes to improving mental component summary score in pregnant women. The likelihood of a mentally healthy pregnancy may be increased by enhancing social capital.