So far, radiation exposure has not been found to have caused any adverse health effects.
Following the accident at the power station, a survey was carried out targeting 2.06 million people in Fukushima Prefecture. The objective was to estimate external doses over a period of four months. Results of the survey estimated the doses for 93.8% of respondents (466,000 people; excluding radiation workers) to be less than 2 mSv.
A committee for the prefecture reviewed the findings, while giving consideration to past epidemiological studies which have been unable to discern significant health effects at doses of ≤100 mSv. The committee took into account the fact that the values were estimates based on a four-month period, but concluded that the radiation levels were unlikely to cause health effects.
Third-party agencies have also made their own assessments. The World Health Organization (WHO) concluded that there were no increased risks to Japan's neighboring countries, and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reported that discernible health effects were unlikely among the population.
Find related information in the following FAQ: Is the safety of Fukushima corroborated by third-party agencies?
Ministry of the Environment Government of Japan: BOOKLET to Provide Basic Information Regarding Health Effects of Radiation Fukushima Minpo&Nagasaki University: Radiation Q&A UNSCEAR: Fukushima 2017 White Paper Fukushima Prefecture Fukushima Reconstruction Station "Health of residents of the prefecture"