At the present time, no health damage arising from radiation exposure has been recognized.
Following the accident at the nuclear power station, a "Basic Survey" targeting approximately 2,060,000 people in Fukushima Prefecture was implemented to estimate external exposure doses over a period of four months after the accident. As a result, it was found that the exposed dose was "less than 2 mSv" among 93.8% of respondents (approximately 466,000 people excluding persons engaged in radiation work).
According to a committee organized on the prefectural level, "Since previous epidemiological studies indicate no significant health effects at doses ≤100 mSv, we concluded that radiation doses estimated so far are unlikely to cause adverse effects on health, although this conclusion is based on external exposure doses estimated only for the first four months following the accident."
Third party agencies, namely the WHO (World Health Organization) and UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation), have also made the following assessments respectively: "increased risk in Japan's neighboring countries is at a negligible level" and "the possibility of health impacts arising in Japanese people is low".
(Also see "Q Is safety in Fukushima Prefecture confirmed 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"