Following the March 2011 Great East Japan Earthquake and the ensuing nuclear disaster at the Fukushima No. 1 power plant, hundreds of nursing-home residents and staffers living close to the plant rushed to evacuate.

But, according to the results of a joint study published Friday in the science journal PLOS ONE, the evacuations posed a far greater health risk to the evacuees than the radiation they would have endured had they decided to stay.

Co-author Masaharu Tsubokura, a University of Tokyo researcher, said the study should be used as a resource in evacuation planning, as many of the nation’s nuclear power plants are waiting for the green light to restart operations.

The researchers, led by Michio Murakami of the University of Tokyo, examined the risks for 191 residents and 184 staffers at three nursing homes 20 to 30 km away from the plant, outside the compulsory evacuation zone.

While all nursing home residents chose to be evacuated due to radiation fears, concerns over the plant’s stability and a lack of resources such as medical drugs, the decision ended up boosting the number of deaths due to the burden of the evacuation itself, changes in medical staff members and a lack of preparation at the sites where patients were sent.

The researchers calculated the “loss of life expectancy” under four scenarios: the next-day evacuation, which is what happened; delayed evacuation three months later; and nonevacuation scenarios with first-year radiation exposures of 20 and 100 millisieverts.

The results showed the next-day evacuation was 400 times more detrimental to the evacuees’ life expectancy than delayed evacuation, and riskier than scenarios where they stayed and were exposed to radiation, which is known to increase the risk of developing cancer.

“The purpose of the study is not to discuss whether the evacuation was appropriate or not,” said Tsubokura. “The study shows that, in preparing for nuclear disasters, evacuation-tied risks need to be reduced through detailed planning in advance.”