BMC Public Health 2008, 8:171 http://www.biomedcentral.com/1471-2458/8/171 increasing birth weight were found to be independent risk factors for obesity. Parental educational level, living space > 75 m2, the number of persons living in the child's living place and breastfeeding for more than three months were found to be inversely associated with overweight. The same factors were inversely related to obesity. In addition, there was evidence for a protective association of attend- ance of day nursery with respect to obesity. Discussion The findings of our multivariable analyses are largely in line with previous investigations of samples of German children of similar age [7-13,21,22]. The study provides further evidence of an inverse associa- tion between parental education and both overweight and obesity in children, as documented by the majority of pre- vious recently published international studies [14]. A finding from the longitudinal 1958 British birth cohort was that social class at birth predicted adult obesity (aged 33 years) in men [30]. It may be speculated that parental educational level at the time of birth or in infancy might be a predictor of overweight/obesity in children, but our study used information on current educational level. However, a change in parental educational level after the birth of children seems unlikely. In a review, Livingstone points out that the association between social factors and childhood obesity is not well understood, and that social factors might interact in dif- ferent ways for different individuals and population groups [31]. For Germany, the studies are consistent in the sense that all studies including the one presented in this paper found an inverse association of a high level of parental education with overweight/obesity [7-11]. The inverse association with living space > 75 m2 may be explained by protective effects of high social status, reflect- ing the fact that more living space becomes affordable with increasing income. More living space could also reflect a higher number of siblings, and the reduced odds could actually be due to not being a single child. However, the inverse association was found in a model controlling for educational level, number of persons in the child's household, and being a single child. Regarding overweight, the protective association of an increasing number of persons in the household could be seen in conjunction with the adverse effect of being a sin- gle child without siblings. Obviously, a social context – either through siblings or other persons in the household or both – confers some kind of protection with respect to overweight. Whether more persons in the household mir- ror a better socio-economic profile, or a closer monitoring of the child's health behaviour, e.g. with regard to eating habits or more opportunities to engage in physical activity with siblings, or whether the effect is mediated via psycho- social pathways remains speculative. The tentative protec- tive association with attendance of day nursery or other- wise being looked after may likewise reflect social status or demonstrate the adverse effect of being neglected as a child on the development of overweight/obesity. A study performed in the West German city of Aachen found that the prevalence of overweight was twice as high in children with other than German nationality as com- pared with native German children [21]. Multivariate analyses showed that most of the difference was explained by know risk factors such as maternal education, watching TV, snacking and consumption of sweets and soft drinks. From this finding, it was concluded that overweight pre- vention should address high-risk environments rather than high-risk ethnic groups. In contrast to this finding, a study in Swiss children found an independent association of non-swiss nationality and overweight [16]. Likewise, our multivariate analysis showed other than German nationality to be a strong independent risk factor for over- weight and obesity, after adjustment for education. This may be due to the major limitation in the multivariate analyses presented which did not include data on dietary habits, physical activity or the time spent watching TV. Low levels of total [17] or vigorous physical activity [16,17] and TV watching [16,18] have been implied as risk factors for childhood overweight/obesity in earlier studies. If they had been measured and were associated with nationality in our study, these variables mighty pos- sibly in part explain the observed relation between nationality and overweight/obesity. We were also unable to adjust for parental overweight and obesity which is a strong predictor for overweight and obesity in children [16,18,32-35]. In a study performed in Northwest Ger- many, the inverse gradient between parental school edu- cation and overweight was even more pronounced in children who had overweight parents [10]. However, in a prospective population-based family study in Eastern Fin- land, a family history of obesity did not seem to be a good predictor of BMI during childhood [36]. With regard to the role of breastfeeding, the study in East German children study found an inverse association with obesity, but not with overweight [8]. This protective effect was stronger if the children were exclusively breastfed. Although this study used the same cut-off points as we did, it should be noted that the study populations are not directly comparable with respect to the age range. The finding of inverse associations between breastfeeding and overweight/obesity confirms the finding of a recent meta- analysis [19] showing that breastfeeding reduced the odds of obesity in childhood (adjusted OR in the fixed model: Page 6 of 10 (page number not for citation purposes)