BMC Public Health 2008, 8:171 http://www.biomedcentral.com/1471-2458/8/171 Background Recent evidence from the German Health Interview and Examination Survey for Children and Adolescents (KiGGS) provides nationally representative data with respect to overweight and obesity in children and adoles- cents (three to 17 years old) for the first time [1]. 15% were classified as overweight and 6.3% were classified obese (exceeding the 90th and 97th percentile of the Ger- man reference data, respectively [2]). Obesity cannot only result in many adverse health out- comes such as respiratory [3], cardiovascular [4] or meta- bolic complications [5] as well as body dissatisfaction [6], but has itself a multifactorial aetiology. Thus, previous studies examined a large number of potential predictors of childhood overweight and obesity. Apart from demonstrating a substantial burden of over- weight and obesity in children and adolescents, the KIGGS study showed overweight or obesity to be associ- ated with lower socioeconomic status, migration back- ground and the mother being overweight. Other studies in samples of German children have identified further fac- tors associated with a lower prevalence of overweight/ obesity, e.g. high parental education [7-11], and factors consistently associated with an increased prevalence, such as maternal smoking during pregnancy [7,9,12,13]. A review of international studies found socio-economic sta- tus to be inversely associated with overweight/obesity [14]. Ethnicity or nationality have also been linked in the patterning of overweight and obesity[15,16]. Little physi- cal activity and watching TV have been implied in the ris- ing prevalence of childhood overweight/obesity [16-18], as well as the consumption of energy-dense foods[16]. Meta-analyses have shown a protective effect of breast- feeding on the risk of overweight/obesity [19,20]. The cited studies used various different cut-off points to categorise overweight/obesity. Most studies used popula- tion-based cut-offs depending on the observed distribu- tion at a given percentile [7,9-13,21] and only a few studies [8,22] used the cut-offs suggested by Cole et al. [23]. Cole and co-authors have developed a definition of overweight and obesity based on pooled samples from several countries, providing age- and sex-specific cut-off points. These reference values are recommended for inter- national comparison [24]. We have previously reported prevalence data for large samples of five to seven-year-old German children (N = 35,434), using the cut-off points proposed by Cole and co-authors [25]. We found significantly increasing preva- lences of overweight and obesity in both East and West Germany from 1991 to 2000. Overall, the prevalence of overweight was 15.5%, and the prevalence of obesity was 4.3%. The aim of this paper is to investigate predictors of child- hood overweight and obesity, drawing on the same data. Methods Study design The study design has been described previously [25]. In brief, data was drawn from the study in school beginners in East and West Germany (SAWO) [26,27], and from the MIRIAM study (Multicenter International Study On Risk Assessment Of Indoor and Outdoor Air Pollution and Eczema Morbidity) [28]. Repeated cross-sectional studies were conducted in several German cities: Borken, Essen, Duisburg, Köln, and Augsburg (MIRIAM) in the West of Germany; Leipzig, Halle, Magdeburg, Merseburg (from 1994), and four small rural towns in the Altmark (Salzwedel, Gardelegen, Osterburg and Kloetze) in the East of Germany. All boys and girls entering primary school between 1991 and 2000 at one of the study sites were eligible to partici- pate. Written consent was obtained from the children's parents. Every three years (1991, 1994, 1997, 2000), ques- tionnaires were sent to the children's parents in the West, with the exception of Augsburg (1996, 2000). In the East, questionnaires were sent each year. Weight and height were measured at the obligatory school entry examina- tions which were held at the local health authorities. Height was measured without shoes and weight was measured in underwear. Ethics approval was obtained from the ethics committees of the medical associations in Bavaria and Saxony-Anhalt, Germany for the original studies. Outcome variables: overweight and obesity Body mass index (BMI) was calculated as weight/ (height)2 [kg/m2]. Our analysis is restricted to five to seven-year-old children. The cut-off points as suggested by Cole et al. [23] increase with age (per additional 6 months of age) and are generally higher for boys than for girls. Exposure variables Besides age and sex, the questionnaire contained informa- tion on socio-demographic characteristics, environmental exposures and early-life factors. The following variables were included: Nationality of the child A child was classified as German if at least one parent reported German nationality. Until 1994 (East) and 1993 (West) the child's nationality was asked directly. Page 2 of 10 (page number not for citation purposes)