Regional variation in the development of neonatal hyperbilirubinemia and relation with sunshine duration in Japan: an ecological study.

Background Few studies have investigated the regional variations in the development of neonatal hyperbilirubinemia. This study aimed to investigate regional variations in medical costs for neonatal hyperbilirubinemia and the correlations between sunshine duration and medical care costs for neonatal hyperbilirubinemia in an ecological study, using the National Database of Japan. Methods We obtained data on the annual medical costs for neonatal hyperbilirubinemia, annual live births, and annual sunshine duration in each prefecture from the National Database of Health Insurance Claims and Specific Health Checkups of Japan (NDB) Open Data, Vital Statistics in Japan, and System of Social and Demographic Statistics Prefectural Data Basic Data from 2014 to 2017. We created choropleth maps showing the regional variations (quartiles) in the annual medical costs for neonatal hyperbilirubinemia per 10 live births and the annual sunshine duration in each prefecture. We used Pearson's correlation coefficients to evaluate the associations between the annual sunshine duration and annual medical care costs for neonatal hyperbilirubinemia per 10 live births in each prefecture. Results The Tohoku region (on the Sea of Japan side) and the Hokuriku region were likely to have higher medical care costs for neonatal hyperbilirubinemia and shorter sunshine duration than the rest of the country. There were weak and negative correlations between the annual sunshine duration and the annual medical care costs for neonatal hyperbilirubinemia. The correlation coefficients ranged from -0.086 to -0.33. Conclusion There could be regional variations in the medical care costs for neonatal hyperbilirubinemia in Japan. Short sunshine duration could be a prognostic factor for the development of neonatal hyperbilirubinemia.