Association of the Great East Japan Earthquake and the Daiichi Nuclear Disaster in Fukushima City, Japan, With Birth Rates

Abstract

Importance: The association of the Great East Japan Earthquake and the subsequent Fukushima Daiichi Nuclear Power Plant disaster of March 11 and 12, 2011, in Fukushima, Japan, with birth rates has not been examined appropriately in the existing literature.

Objective: To assess the midterm and long-term associations of the Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant disaster with birth rates.

Design, setting, and participants: Cohort study in which interrupted time series analyses were used to assess monthly changes in birth rates among residents of Fukushima City, Japan, from March 1, 2011, to December 31, 2017, relative to projected birth rates without the disaster based on predisaster trends. Birth rates from January 1, 2007, to December 31, 2017, in Fukushima City were determined using information from the Fukushima City government office.

Exposure: The Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant disaster, expressed via 5 potential models of the association with birth rate: level change, level and slope changes, temporal level change, and temporal level change with 1 or 2 slope change(s).

Main outcomes and measures: Birth rate, calculated from monthly data on the number of births and total population.

Results: The mean birth rate before the Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant disaster was 69.8 per 100 000 people per month; after the disaster, the mean birth rate was 61.9 per 100 000 people per month. Compared with birth rates before the Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant disaster, there was an estimated 10% reduction in monthly birth rates in Fukushima City (rate ratio, 0.90; 95% CI, 0.86-0.93) in the first 2 years after the disaster. After that, the birth rate trend was similar to the predisaster trend. The predisaster trend suggested a continuous decrease in birth rate (rate ratio for 1 year, 0.98; 95% CI, 0.98-0.99). This gap model was optimal and parsimonious compared with others. A similar association was found when trimonthly averaged data were analyzed.

Conclusions and relevance: The Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant disaster were followed by significant reductions in birth rates for 2 years. There was insufficient evidence to indicate that the trend in the 3 to 7 years after the disaster differed from the predisaster trends. The recovery from the reductions in the birth rate may be indicative of the rebuilding efforts. The continuing long-term decrease in birth rates observed before the Great East Japan Earthquake and the Fukushima Daiichi Nuclear Power Plant disaster suggests that continuing measures to support birth planning should be considered at the administrative level.

Figure.. Trend in Birth Rates Estimated From Interrupted Time Series Analysis

The trend in birth rates was estimated using the Poisson regression model, including the temporal level change (gap) and the indicator variable of the calendar month. The rate ratio during the 2 years after the Fukushima Daiichi Nuclear Power Plant disaster was 0.90 (95% CI, 0.86-0.93). The dots indicate observed birth rates. The vertical line indicates the time of the Fukushima Daiichi Nuclear Power Plant disaster between February and March 2011.