Claim: The incidence of thyroid cancer is approximately 230 times higher than normal in Fukushima Prefecture, presumably due to the Fukushima disaster.
Summary: The larger claims come from a misreading of statistics. Most experts, looking at the same data, believe that Fukushima has had little to no effect on thyroid cancer prevalence.
Claim found in EENews, Duluth Reader, HealthMoneyVine. Spread far and wide by InfoWars. It originates from a video presentation from the Fairewinds Energy Education site, where a speaker refers to a report from Japan that he claims shows an incidence in Fukushima Prefecture of thyroid cancer that is 230 times the normal level.
Incidence of detected thyroid cancer in children is up near Fukushima, but the result likely has nothing to do with radiation. Rather. what has happened is a classic screening issue. It turns out that many more children than previously though have thyroid abnormalities young in life. However, the vast majority of children are never screened for such abnormalities, so reported incidence is low. We explain this screening issue below.
After the disaster, worried about Chernobyl-like repercussions, the authorities did a general screening of all children. The idea of the screenings was not to check for effects of the disaster, but to get a baseline number so that they could look at increase. After all, the first effects of the disaster shouldn't have been until at least four years after the event.
What they found did surprise them – a lot of the children already had thyroid abnormalities. Out of the approximately 300,000 children scanned for thyroid cancer in these baseline scans, 110 showed the presence of cancer cells in a needle aspiration biopsy, Taken at face-value, this would represent a 30-fold increase in thyroid cancer incidence. A paper published in the prestigious journal Epidemiology made that case, arguing this was a leading indicator of a looming health crisis.
The Epidemiology paper, however, was widely criticized by the epidemiology community, who rejected the comparison laid out by the author. Most experts believe the level of incidence is about the screening, not the disaster. Researchers can't compare results of a universal screening to the results of screenings that come as a result of patients demonstrating thyroid cancer symptoms. The reason is that only a small amount of thyroid cancer causes individuals issues – meaning that numbers in the general (non-screened) population will always be dramatically lower than numbers in a universally screened population.
Here's an explanation from Science in 2016:
“The evidence suggests that the great majority and perhaps all of the cases so far discovered are not due to radiation,” says Dillwyn Williams, a thyroid cancer specialist at University of Cambridge in the United Kingdom. In journal papers and in a series of letters published last month in Epidemiology, scientists have attacked the alarmist interpretations.
They go on to point out that when incidence rates are compared with other general screenings, the thyroid cancer rates of Fukushima residents are similar to places not exposed to radiation.