The preliminary health report showed an increase in children from kindergarten to high school age who weighed 20 per cent more than the standard as per their height.
Fifty-six per cent of public schools in Fukushima had curtailed outdoor activities during school time as of June last year to minimise exposure to radiation released from the crippled Fukushima No 1 atomic plant, Kyodo news agency reported.
According to the prefectural board of education, such restrictions were still in place at 71 elementary and junior high schools this September. It is believed schools based the amount of time they allowed kids to spend outdoors on local atmospheric radioactive fallout readings.
The obesity trend was noticeable among early elementary school students, with the rate among first-graders standing at 9.7 per cent, up 4.7 percentage points from the previous survey in 2010 through March 2011.
According to the report, the rate for third-graders came to 13.5 per cent, up 5.1 points.
For ninth-graders, the rate was 11.5 per cent, up 0.6 point, while that for high school seniors stood at 14.1 per cent, up 1.4 points, according to the survey based on health checkups conducted between April and June this year.
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It has been found that children in northern regions that experience more severe winters are prone to gain weight because they curb outdoor activities when it's cold, the report said.
However, a ministry official said the obesity trend among Fukushima children should not be attributed only to the usual cold winters, and the report also did not indicate that its findings were linked to seasonal factors.