Soon after the Fukushima nuclear crisis began, Mike Sebourn says he began noticing changes in his body. First came nosebleeds, headaches and nausea. In August 2011 the symptoms worsened. Previously fit and strong, he began to lose energy and experience excruciating pain.

Today, the former U.S. Navy officer says one side of his body has withered. "My right arm is about an inch-and-a-half smaller than my left; my leg, too. Nobody can figure out what's wrong." After 17 years' service on American military bases in Japan, he has been forced to retire — aged 37.

Sebourn fears his condition was triggered by his job during Operation Tomodachi, the huge relief mission mounted by the U.S. military during the March 2011 disaster. After the Fukushima No. 1 nuclear plant went into meltdown on March 11, he was dispatched to Misawa Air Base in far-northern Aomori Prefecture to check helicopters for radiation.