ISSN 0931-4288

No. 622-623, Dec. 6, 2012www.strahlentelex.de

Infant mortality in Japan after Fukushima

revised English version

Dr Alfred Koerblein
alfred.koerblein@gmx.de10 January 2013
Summary
Following the nuclear disaster at Fukushima Dai-ichi in March 2011, Japanese infant mortality monthly
data exhibit distinct peaks in May 2011 and December 2011, 2 and 9 months respectively after thedisaster. After Chernobyl, an analysis of early infant mortality data in West Germany found significant
peaks in June 1986 and February 1987, i.e. at similar time lags after the Chernobyl disaster in April 1986.
In December 2011, 9 months after Fukushima, there is also a significant deficit in the number of live
births in Japan. A similar decline in birth numbers was found in February 1987 in southern Bavaria, theGerman region most affected by Chernobyl fallout. In Japan as well as Bavaria, the effect is limited to asingle month.
Background
The first health effects from the catastrophic accident at the nuclear power plant in Fukushima Dai-ichi
on 11 March 2011 might be expected to be seen in infant mortality data. A German study [1] after theChernobyl accident in April 1986 showed noticeable increases in early infant mortality (ie mortality
within 0-6 days of birth) in June 1986 and at the beginning and the end of 1987. The maximum inFebruary 1987 is interpreted [1] to be due to damage to the embryo at a critical stage of pregnancy.
From the German experience, a similar increase in infant mortality in Japan after Fukushima could beexpected.
Data and Methods
Monthly data of infant mortality from Japan can be found on the website of the Japanese Ministry of
Health and Labour, http://www.mhlw.go.jp/toukei/list/81-1a.html. An English translation of the required
data, i.e. the numbers of live births and infant deaths, was provided by Dr Masao Fukumoto. Germanmonthly data of early infant mortality data for 1980 to 1993 were obtained from Statistisches
Bundesamt in Wiesbaden, https://www.destatis.de/DE/Startseite.html.
Monthly infant mortality rates from January 2002 to March 2011 are analyzed with linear logisticregression. Seasonal variations are modeled by dummy variables for February through December, withJanuary as the reference month. The course of the data from April 2011 to May 2012 is compared withthe extrapolated trend of the data before Fukushima.
Using Poisson regression, data of live births are analyzed to test for a possible drop in December 2011, 9months after the disaster in March 2011. As above, 11 dummy variables account for seasonal effects.

Results(a) Infant mortality
The regression model yields a good fit to the data from 2002 to March 2011 (deviance = 86.0, df = 98).
Figure 1a shows infant mortality rates and the long-term trend. After Fukushima, pronounced peaks ininfant mortality are found in May 2011 (observed cases (O) = 247, expected cases (E) = 208.9, excess =38.1) and in December 2011 (O=240, E=203.3, excess=36.7). Figure 1b displays the residuals, i.e. thedifferences between observed and expected rates, in units of standard deviations. The broken lines
indicate the range of 2 standard deviations in which 95% of the data points should normally lie.
Figures 2a and 2b show the results of a combined regression analysis of the data from Fukushima
prefecture and from Japan without Fukushima. A significant 3-fold increase of infant mortality is found inFukushima prefecture in May 2011 (O=9, E=3.1, P=0.0014).
The Japanese results were compared with the results of an analysis of monthly data of early infantmortality in West Germany, 1980 to 1993 (Figures 3a, 3b). Significant increases are found in June 1986,February 1987, and November 1987.
The mortality peaks in February 1987 and November 1987 in the German data are shown in [1] to be
associated with peaks of cesium burdens in pregnant women. In particular, the November 1987 peakfollows an increase in the cesium content of cows’ milk during the winter 1986/87 when cows were fed
cesium-contaminated silage [1].
The peaks in the Japanese data in May 2011 and December 2011, two and nine months after the nuclear
disaster, parallel mortality peaks in the German data in June 1986 and February 1987 after the Chernobyl
disaster on 26 April 1986.
(b) Decline in numbers of live births
Interestingly, there are also statistically significant reductions in the number of live births in December
2011 in Japan as a whole (minus 4.7%, P=0.0072, see Figures 4a, 4b) and, more pronounced, inFukushima prefecture (minus 15.1%, P=0.0001). In the previous month (November 2011) and thefollowing month (January 2012), birth numbers are not significantly decreased.
A similar effect is found after Chernobyl in Bavaria. In February 1987, 9 months after the nuclear
disaster, the number of births fell by 8.8% relative to the expected value (P=0.0083). As in Japan, thedecrease is limited to a single month (February 1987); no effect is seen in January 1987 and March 1987.
In southern Bavaria, where cesium soil contamination was significantly higher than in northern Bavaria,
the decline in births is more pronounced (minus 11.5%, P=0.0009, see Figures 5a, 5b) than in northern
Bavaria (minus 5.2%, P=0.151). The cause of the falling birth rate could be a radiation-induced loss ofzygotes shortly after fertilization.
[1] Körblein A, Küchenhoff H. Perinatal mortality in Germany following the Chernobyl accident. Radiat
Environ Biophys. 1997 Feb;36(1):3-7.
Available at: http://www.alfred-koerblein.de/chernobyl/downloads/KoKu1997.pdf

Fig.1a (upper diagram): Monthly infant mortality rates in Japan and trend line. The vertical broken line
indicates the end of March 2011.
Fig.1b (lower diagram): Deviations of infant mortality rates from the expected trend in units of standard
deviations (standardized residuals) and 3-month moving average (solid line). The horizontal broken lines
show the range of two standard deviations.

Fig.2a: Monthly infant mortality rates in Fukushima prefecture (black dots) and in Japan without
Fukushima (open circles).
Fig.2b: Deviations of infant mortality rates in Fukushima prefecture from the expected trend, in units ofstandard deviations (standardized residuals), and 3-month moving average (solid line). The horizontal
broken lines show the range of two standard deviations.

Fig.3a: Early infant mortality rates (0-6 days) in West Germany and trend line. The vertical broken line
indicates the end of April 1986.
Fig.3b: Deviations of early infant mortality rates in West Germany from the expected trend in units ofstandard deviations (standardized residuals), and 3-month moving average (solid line).

Fig.4a: Monthly numbers of live births in Japan
Fig.4b: Deviations of the numbers of live births from the expected numbers, in units of standard
deviations (standardized residuals). The horizontal broken lines show the 95% prediction limits.

Fig.5a: Monthly numbers of live births in southern Bavaria
Fig.5b: Deviations of the numbers of live births from the expected numbers, in units of standard
deviations (standardized residuals). The horizontal broken lines show the 95% prediction limits.