Trends in unintentional injury–related mortality rates in the metropolitan and non-metropolitan areas of Japan from 1999 to 2023

Background To our knowledge, no study has investigated the trends in unintentional injury–related mortality rates in relation to urbanisation level in recent decades in Japan. We investigated the differences in such mortality trends between the country’s metropolitan and non-metropolitan areas. Methods This retrospective study analysed aggregate data on unintentional injury–related mortality from 1999 to 2023, obtained from Japan’s official Vital Statistics. Data on all unintentional injuries, traffic injuries, falls, drowning and suffocation were used. Age-standardised mortality for each type of unintentional injury was calculated by year, sex and area (metropolitan or non-metropolitan), and the ratio of the age-standardised mortality rates between metropolitan and non-metropolitan areas was calculated by injury type, year and sex. The annual percentage change in age-standardised mortality rate was also calculated by injury type, area and sex. Results Age-standardised mortality rates for all unintentional injuries, traffic injuries and suffocation decreased over the studied period, with the rates in non-metropolitan areas being higher than those in metropolitan areas. In contrast, the age-standardised mortality rates for drowning in metropolitan areas were higher. In addition, a statistically significant decrease was observed in the age-standardised mortality rates for all unintentional injuries, traffic injuries and suffocation, regardless of sex and area; notably, the degree of decrease was larger in non-metropolitan areas. Conclusions The disparity in mortality rates between the areas decreased over time for all unintentional injuries, and the decrease in rates for traffic injuries and suffocation was more pronounced in non-metropolitan areas.