We tested whether a simple overweight prevention program promoting water consumption in elementary schools is equally effective in children with an immigrational background (MIG) and in those without (non-MIG). Thus, a secondary analysis of a controlled cluster trial, lasting one school year, was conducted. Thirty-two elementary schools located in low socioeconomic districts in two German cities were included. Of the 2,950 school children analyzed, 1,306 were MIG children. Water fountains were installed in the schools of the intervention group (IG) and teachers held lessons to promote water consumption. Control schools (control group (CG)) did not receive any intervention. Before and after intervention, body weight and height was measured. Overweight was defined by age- and sex-specific BMI cutoffs that are linked to an adult BMI of 25 kg/m(2). Beverage consumption was assessed in questionnaires. Modification of intervention effects by immigrational background was tested by interaction terms. The immigrational background modified the intervention effect on prevalence and remission of overweight (interaction term: P = 0.03 and P = 0.02), but not on the incidence of overweight (P = 0.06). After intervention, the risk of being overweight was reduced in the IG compared to the CG among non-MIG (odds ratio = 0.51, 95% confidence interval (CI): 0.31-0.83), but not among MIG children (odds ratio = 1.02, 95% CI: 0.63-1.65). After intervention, water consumption significantly increased in the IG equally among both, non-MIG and MIG, by ~1 glass/day. A simple school-based intervention promoting water consumption prevented overweight in non-MIG children, but failed in MIG children. Different beverage consumption, among other lifestyle factors, may account for this effect but scientific discussion remains open.
Trial registration: ClinicalTrials.gov NCT00554294.