Many meta-analyses use a random-effects model to account for heterogeneity among study results, beyond the variation associated with fixed effects. A random-effects regression approach for the synthesis of 2 x 2 tables allows the inclusion of covariates that may explain heterogeneity. A simulation study found that the random-effects regression method performs well in the context of a meta-analysis of the efficacy of a vaccine for the prevention of tuberculosis, where certain factors are thought to modify vaccine efficacy. A smoothed estimator of the within-study variances produced less bias in the estimated regression coefficients. The method provided very good power for detecting a non-zero intercept term (representing overall treatment efficacy) but low power for detecting a weak covariate in a meta-analysis of 10 studies. We illustrate the model by exploring the relationship between vaccine efficacy and one factor thought to modify efficacy. The model also applies to the meta-analysis of continuous outcomes when covariates are present.

ABSTRACT. Objective. Obesity increases risk of many adverse outcomes, but its early origins are obscure. Gestational diabetes mellitus (GDM) reflects a metabolically altered fetal environment associated with high birth weight, itself associated with later obesity. Previous studies of GDM and offspring obesity, however, have been few and conflicting. The objectives of this study were to examine associations of birth weight and GDM with adolescent body mass index (BMI) and to determine the extent to which the effect of GDM is explained by its influence on birth weight or by maternal adiposity.Methods. We conducted a survey of 7981 girls and 6900 boys, 9 to 14 years of age, who are participants in the Growing Up Today Study, a US nationwide study of diet, activity, and growth. In 1996, participants reported height, weight, diet, activity, and other variables by selfadministered mailed questionnaire. We linked these data with information reported by their mothers, participants in the Nurses' Health Study II, including GDM, height, current weight, and child's birth weight. We excluded births <34 weeks' gestation and mothers who had preexisting diabetes. We defined overweight as BMI (kg/m 2 ) >95th percentile, and at risk for overweight as 85th to 95th percentile, for age and gender from US national data.Results. Mean birth weight was 3.4 kg for girls and 3.6 kg for boys. Among the 465 subjects whose mothers had GDM, 17.1% were at risk for overweight and 9.7% were overweight in early adolescence. In the group without maternal diabetes, these estimates were 14.2% and 6.6%, respectively. In multiple logistic regression analysis, controlling for age, gender, and Tanner stage, the odds ratio for adolescent overweight for each 1-kg increment in birth weight was 1.4 (95% confidence interval: 1.2-1.6). Adjustment for physical activity, television watching, energy intake, breastfeeding duration, mother's BMI, and other maternal and family variables reduced the estimate to 1.3 (1.1-1.5). For offspring of mothers with GDM versus no diabetes, the odds ratio for adolescent overweight was 1.4 (1.1-2.0), which was unchanged after controlling for energy balance and socioeconomic factors. Adjustment for birth weight slightly attenuated the estimate (1.3; 0.9 -1.9); adjustment for maternal BMI reduced the odds ratio to 1.2 (0.8 -1.7).Conclusions. Higher birth weight predicted increased risk of overweight in adolescence. Having been born to a mother with GDM was also associated with increased adolescent overweight. However, the effect of GDM on offspring obesity seemed only partially explained by its influence on birth weight, and adjustment for mother ' R ates of obesity among children as well as adults in the United States have been rising during the past 4 decades. 1-3 Adolescent obesity is strongly associated with adult obesity and predicts both short-and long-term adverse health outcomes. 4 -11 Research into early-life determinants of obesity could lead to innovative strategies for prevention.Evidence from animal and human studie...

Infants who were fed breast milk more than infant formula, or who were breastfed for longer periods, had a lower risk of being overweight during older childhood and adolescence.

BERKEY, CATHERINE S., HELAINE R.H. ROCKETT, ALISON E. FIELD, MATTHEW W. GILLMAN, AND GRAHAM A. COLDITZ. Sugar-added beverages and adolescent weight change. Obes Res. 2004;12:778 -788. Objective: The increase in consumption of sugar-added beverages over recent decades may be partly responsible for the obesity epidemic among U.S. adolescents. Our aim was to evaluate the relationship between BMI changes and intakes of sugar-added beverages, milk, fruit juices, and diet soda. Research Methods and Procedures: Our prospective cohort study included Ͼ10,000 boys and girls participating in the U.S. Growing Up Today Study. The participants were 9 to 14 years old in 1996 and completed questionnaires in 1996, 1997, and 1998. We analyzed change in BMI (kilograms per meter squared) over two 1-year periods among children who completed annual food frequency questionnaires assessing typical past year intakes. We studied beverage intakes during the year corresponding to each BMI change, and in separate models, we studied 1-year changes in beverage intakes, adjusting for prior year intakes. Models included all beverages simultaneously; further models adjusted for total energy intake. Results: Consumption of sugar-added beverages was associated with small BMI gains during the corresponding year Analyses of year-to-year change in beverage intakes provided generally similar findings; boys who increased consumption of sugar-added beverages from the prior year experienced weight gain (ϩ0.04 kg/m 2 per additional daily serving, p ϭ 0.01). Children who increased intakes by 2 or more servings/d from the prior year gained weight (boys: ϩ0.14, p ϭ 0.01; girls ϩ0.10, p ϭ 0.046). Further adjusting our models for total energy intake substantially reduced the estimated effects, which were no longer significant. Discussion: Consumption of sugar-added beverages may contribute to weight gain among adolescents, probably due to their contribution to total energy intake, because adjustment for calories greatly attenuated the estimated associations.

For both boys and girls, a 1-year increase in BMI was larger in those who reported more time with TV/videos/games during the year between the 2 BMI measurements, and in those who reported that their caloric intakes increased more from 1 year to the next. Larger year-to-year increases in BMI were also seen among girls who reported higher caloric intakes and less physical activity during the year between the 2 BMI measurements. Although the magnitudes of these estimated effects were small, their cumulative effects, year after year during adolescence, would produce substantial gains in body weight. Strategies to prevent excessive caloric intakes, to decrease time with TV/videos/games, and to increase physical activity would be promising as a means to prevent obesity.

Our results suggest that parents and the media influence the development of weight concerns and weight control practices among preadolescents and adolescents. However, there are gender differences in the relative importance of these influences.

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BACKGROUND:Several cross-sectional studies reported that heavier children eat breakfast less often. However, no longitudinal studies have addressed whether skipping breakfast leads to excessive weight gain. OBJECTIVE: To investigate whether skipping breakfast was prospectively associated with changes in body fatness. METHODS: A cohort of 414 000 boys and girls from all over the US, 9-to 14-y-old in 1996, returned annual mailed questionnaires (1996)(1997)(1998)(1999) for the Growing Up Today Study. We analyzed change in body mass index (BMI; kg/m 2 ) over three 1-y periods among children who reported breakfast frequency. RESULTS: Children who reported that they never eat breakfast had lower energy intakes than those who eat breakfast nearly every day. Children who were more physically active reported higher energy intakes, as did those who reported more time watching television/videos and playing videogames. Like previous studies, skipping breakfast was associated with overweight, cross-sectionally. However, overweight children who never ate breakfast lost BMI over the following year compared to overweight children who ate breakfast nearly every day (boys: À0.66 kg/m 2 (s.e. ¼ 0.22); girls: À0.50 kg/m 2 (s.e. ¼ 0.14)). But normal weight children who never ate breakfast gained weight relative to peers who ate breakfast nearly every day (boys: +0.21 kg/m 2 (s.e. ¼ 0.13); girls: +0.08 kg/m 2 (s.e. ¼ 0.05)). Breakfast frequency was positively correlated with self-reported quality of schoolwork. CONCLUSIONS: Overweight children who never eat breakfast may lose body fat, but normal weight children do not. Since numerous studies link skipping breakfast to poorer academics, children should be encouraged to eat breakfast.