Residents of Fukushima and neighboring prefectures, let alone Tokyo, have little to fear from radiation exposure because current levels are far below what would pose a health risk, a newly appointed medical adviser to Fukushima Prefecture said Tuesday.

Speaking at the Foreign Correspondents' Club of Japan, Shunichi Yamashita, a professor at the Graduate School of Biomedical Sciences at Nagasaki University, said, "You don't have to worry about staying in Tokyo."

The likelihood of contracting cancer increases slightly with a single exposure exceeding 100 millisieverts, said Yamashita, an authority on the effects of radiation exposure from the atomic bombings and the Chernobyl nuclear reactor disaster.

By comparison, the highest level of radiation recorded in Fukushima — 0.0152 millisieverts — was in the village of Iitate, 40 km northwest of the plant, at 5 p.m. Tuesday, according to the Fukushima Prefectural Government website.

In Tokyo, the maximum reading between 9 a.m. Monday and 9 a.m. Tuesday was 0.000142 millisievert, according to the Education, Culture, Sports, Science and Technology Ministry.

Exposure to 100 millisieverts of radiation at one time carries a much higher health risk than cumulative exposure to that amount in small doses over time, Yamashita said.

There is no need for anyone farther than 20 km from the leaking nuclear plant to take potassium iodide to protect their thyroid glands from radioactive iodine, the professor said.

He said his main concern is food such as spinach and milk. He added that seafood caught near Fukushima should also be monitored.

The government decided Monday to ban shipments of spinach and a local vegetable called "kakina" from Fukushima, Tochigi, Gunma and Ibaraki prefectures. Shipments of milk from Fukushima have also been suspended.