The objective was to investigate the association between early and late maternal smoking during pregnancy on offspring body mass index (BMI). We undertook a retrospective cohort study using linked records from the Women’s and Children’s Health Network in South Australia. Among a cohort of women delivering a singleton, live-born infants between January 2000 and December 2005 (n=7658), 5961 reported not smoking during pregnancy, 297 reported quitting smoking during the first trimester of pregnancy, and 1400 reported continued smoking throughout pregnancy. Trained nurses measured the height and weight of the children at preschool visits in a state-wide surveillance programme. The main outcome measure was age- and sex-specific BMI z-score. At 4 to 5 years, mean (s.d.) BMI z-score was 0.40 (1.05), 0.60 (1.07) and 0.65 (1.18) in children of mothers who reported never smoking, quitting smoking and continued smoking during pregnancy, respectively. Compared with the group of non-smokers, both quitting smoking and continued smoking were associated with an increase in child BMI z-score of 0.15 (95% confidence interval: 0.01–0.29) and 0.21 (0.13–0.29), respectively. A significant dose–response relationship was also observed between the number of cigarettes smoked per day on average during the second half of pregnancy and the increase in offspring BMI z-score (P<0.001). In conclusion, any maternal smoking in pregnancy, even if mothers quit, is associated with an increase in offspring BMI at 4 to 5 years of age.

The aim of this review is to examine two factors that may be associated with development of childhood overweight: early feeding, namely exclusive breastfeeding practices; family structure. Findings from the Identification and prevention of Dietary- and lifestyle-induced health EFfects In Children and infantS (IDEFICS) study are presented in the context of the literature. IDEFICS is a multi-centre European study exploring the risks for overweight and obesity in children, which recruited 16 224 children aged 2–9 years from September 2007 to June 2008 at survey centres in Italy, Estonia, Cyprus, Belgium, Sweden, Hungary, Germany and Spain. Among the IDEFICS sample, after controlling for confounders, exclusive breastfeeding for 4–6 months was protective of overweight (including obesity) when compared with children never exclusively breastfed (OR 0·73, 95 % CI 0·63, 0·85). Family structure and number of siblings may also be associated with overweight. IDEFICS children without siblings were more likely (OR 1·52, 95 % CI 1·34, 1·72) to be overweight than their peers with siblings when controlling for factors related to childhood overweight such as country, parental education, parental weight, maternal age, child's age, birth weight and gender. Both early feeding practices and family structure play a role in the future development of obesity. The impact of breastfeeding on future development of overweight is dependent upon the dose. Exclusive breastfeeding for the recommended 6 months appears to be protective of overweight. Family structure is also an important component and emerging research suggests only children are at increased risk for overweight in comparison with those with siblings. In European countries, approximately 22 million children are overweight. Early dietary exposures, genetic, environmental and social factors have all been proposed as potential causal factors. Two such factors include exclusive breastfeeding and the impact of being an only child. We have investigated these two factors for associations with overweight; our studies, in the context of previous findings, are the focus of this review.

Leptin is an adipocyte-secreted hormone which plays a key role in energy homeostasis. Our aim was to determine the relationship between serum leptin and clinical and biochemical features in overweight children and adolescents. Overweight children and adolescents followed in this Unit with serum leptin ascertained were included. Clinical, biochemical and abdominal ultrasound data were analysed. Statistical analysis was performed by t test, χ2, Pearson's correlation and linear regression. One outlier of serum leptin was excluded to perform correlation and regression. Serum leptin was determined in 357 patients. At the first visit, the mean age was 9·5 (sd 3·2) years and mean BMI z-score was 1·72 (sd 1·34) (girls 1·71 (sd 1·16); boys 1·72 (sd 1·11)). Serum leptin levels were significantly related to: sex (mean: girls 48·0 ng/ml, boys 34·4 ng/ml; P = 0·003); Tanner stage (mean: I–II 37·0 ng/ml, III–V 45·2 ng/ml; P = 0·035); systolic blood pressure (mean: normal 41·3 ng/ml, high 44·0 ng/ml; P = 0·009); BMI z-score (r 0·136; P = 0·010); C-peptide (r 0·17; P = 0·002); insulin (r 0·34; P < 0·001); homeostasis model assessment of insulin resistance (HOMA-IR) (r 0·25; P < 0·001) and aspartate aminotransferase (r − 0·12; P = 0·023). In the multivariate analysis (with leptin as the dependent variable and sex, Tanner stage, BMI z-score, systolic blood pressure, aspartate aminotransferase, C-peptide, insulin and HOMA-IR as independent variables), sex and BMI were determinant factors. The present study in overweight children and adolescents showed that being female and greater BMI were significantly and independently associated with increased serum leptin. In this large cohort other associations with leptin described in the literature can be discharged.

There have been only a few controlled studies on the prevention of overweight and obesity in children and adolescents. These studies differ in relation to strategy, setting, duration, focus, variables of outcome and statistical power, and therefore do not allow general conclusions to be made about the value of preventive measures. All school-based interventions aimed at the prevention of overweight and obesity show some improvement of health knowledge and health-related behaviours. Short-term effects on nutritional state seem to be more pronounced in girls than in boys. School-based interventions can reduce the incidence of overweight. There is evidence that families of intermediate and high socio-economic status as well as intact families benefit more from treatment than families sharing other characteristics. Selected prevention in obese children is most successful when children are treated together with their parents. However, there are social barriers limiting the success of family-based interventions. Although some positive effects have been reported, simple interventions in a single area (e.g. a school health education programme) are unlikely to work on their own. The development of effective preventive interventions probably requires strategies that affect multiple settings simultaneously. At present there is no concerted action, rather many strategies in health promotion that are followed in isolation. Faced with the epidemic of overweight there is a need for national campaigns and action plans on childhood overweight and obesity. It is tempting to speculate that this strategy will also increase the value of isolated approaches (e.g. in schools and families).