Background The recent economic recession represents an opportunity to test whether decreases in economic resources may have deleterious consequences on childhood overweight/obesity risk.

Methods We investigated the association between indicators of changing macroeconomic conditions from 2008 to 2012 and overweight/obesity risk among school-aged children in California (n=1 741 712) using longitudinal anthropometric measurements. Multivariate regression, with individual and county fixed effects, was used to examine the effects of annual county-level unemployment and foreclosure rates on risk of child overweight/obesity, overall and among subgroups (race/ethnicity, sex, county-level median household income and county-level urban/rural status).

Results From 2008 to 2012, ∼38% of children were overweight/obese and unemployment and foreclosure rates averaged 11% and 6.9%, respectively. A 1-percentage point (pp) increase in unemployment was associated with a 1.4 pp (95% CI 1.3 to 1.5) increase in overweight/obesity risk. Therefore, a child of average weight could expect a 14% increase in their body mass index z-score in association with a 1 pp increase in unemployment during the study period. We found some differences in the magnitude of the effects for unemployment among demographic subgroups, with the largest effects observed for unemployment among American Indians and Pacific Islanders.

Conclusions Comparing children to themselves over time, we provide evidence that increases in county-level unemployment are associated with increased overweight/obesity risk. Given that overweight among children with lower economic resources remains a challenge for public health, these findings highlight the importance of policy-level approaches, which aim to mitigate the impact of decreased resources as economic conditions change.