Objective
Radiation fears following Japan’s 2011 Fukushima nuclear disaster impacted levels of physical activity in local children. We assessed the post- versus pre-disaster weight status in school children, and evaluated to what extent school restrictions on outdoor activities that were intended to reduce radiation exposure risk affected child weight.

Participants
We considered children aged 13–15 years from four of the five secondary schools in Soma City (n=1,030, 99.1% of all children in the city), located in 35–50 km from the Fukushima nuclear plant, post- (2012 and 2015) and pre-disaster (2010).

Methods
Weight status, in terms of body mass index (BMI), percentage of overweight (POW), and incidence of obesity and underweight (defined as a POW ≥ 20% and ≤ -20%, respectively), were examined and compared pre- and post-disaster using regression models. We also constructed models to assess the impact of school restrictions on outdoor activity on weight status.

Results
After adjustment for covariates, a slight decrease in mean BMI and POW was detected in females in 2012 (-0.37, 95% CI: -0.68 to -0.06; and -1.97, 95% CI: -3.57 to -0.36, respectively). For male children, obesity incidence increased in 2012 (odds ratio for obesity: 1.45, 95% CI: 1.02 to 2.08). Compared to pre-disaster weight status, no significant weight change was identified in 2015 in either males or females. School restrictions on outdoor activities were not significantly associated with weight status.

Conclusions
Four years following the disaster, weight status has recovered to the pre-disaster levels for both males and females; however a slight decrease in weight in females, and a slight increased risk of obesity was observed in males one year following the disaster. Our findings could be used to guide actions taken during the early phase of a radiological disaster to manage the post-disaster health risks in adolescent children.