LONDON - Two years after Japan's nuclear plant disaster, an international team of experts said Thursday that residents of areas hit by the highest doses of radiation face an increased cancer risk so small it probably won't be detectable.
In fact, experts calculated that increase at about 1 extra percentage point added to a Japanese infant's lifetime cancer risk.
"The additional risk is quite small and will probably be hidden by the noise of other (cancer) risks like people's lifestyle choices and statistical fluctuations," said Richard Wakeford of the University of Manchester, one of the authors of the report. "It's more important not to start smoking than having been in Fukushima."
The report was issued by the World Health Organization, which asked scientists to study the health effects of the disaster in Fukushima, a rural farming region.
On March 11, 2011, an earthquake and tsunami knocked out the Fukushima plant's power and cooling systems, causing meltdowns in three reactors and spewing radiation into the surrounding air, soil and water. The most exposed populations were directly under the plumes of radiation in the most affected communities in Fukushima, about 150 miles north of Tokyo.
In the report, the biggest increases in risk are for people exposed as babies to radiation in the most heavily affected areas. Normally in Japan, the lifetime risk of developing cancer of an organ is about 41 percent for men and 29 percent for women. The new report said that for infants in the most heavily exposed areas, the radiation from Fukushima would add about 1 percentage point to those numbers.
Experts had been particularly worried about a spike in thyroid cancer, since radioactive iodine released in nuclear accidents is absorbed by the thyroid, especially in children. After the Chernobyl disaster in Ukraine, about 6,000 children exposed to radiation later developed thyroid cancer because many drank contaminated milk after the accident.
In Japan, dairy radiation levels were monitored closely, but children are not big milk drinkers there.
The WHO report estimated that women exposed as infants to the most radiation after the Fukushima accident would have a 70 percent higher chance of getting thyroid cancer in their lifetimes. But thyroid cancer is extremely rare and one of the most treatable cancers when caught early. A woman's normal lifetime risk of developing it is about 0.75 percent. That number would rise by 0.5 under the calculated increase for women who got the highest radiation doses as infants.
Wakeford said the increase may be so small it probably will not be observable.