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A new analysis shows that childhood thyroid cancer rates in the Fukushima Prefecture are about 20 to 50 times the Japanese national average.

In 2013, the World Health Organization listed thyroid cancer as a possible health risk

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in a report on the Fukushima disaster. But the question of whether or not cancer cases can be linked to the accident is a divisive one. Since children’s thyroids are still growing and therefore more susceptible to damage, a studying correlating thyroid cancer rates and radiation is at least suggestive—if not altogether flawless.

In a large public health survey led by Toshihide Tsuda of Okayama University, children living near the Fukushima Dai-ichi power plant at the time of the energy disaster were offered regular thyroid screenings; the researchers ended up testing 370,000 residents aged 18 and younger. Tsuda and his colleagues published their results in the journal Epidemiology. The highest incidence rate ratio, they report, was observed in the central middle district of the prefecture compared to the overall Japanese annual incidence, and the prevalence of thyroid cancer was 605 per one million.

The scientists claim their findings are unlikely to be explained by an increase in screenings throughout the Fukushima prefecture—but Japanese officials disagree.

Meanwhile, some scientists say the results are misleading for other reasons. Geoff Brumfiel, reporting for NPR :

David Brenner, director of the Center for Radiological Research at Columbia University, adds that the study makes no effort to trace the exposure of patients. “It’s simply relating geographic regions to cancer risks and not looking at individual radiation doses,” he says, adding that without that information, it’s virtually impossible to connect the screenings to the accident. “It really doesn’t tell us the whole story,” he says.

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