Predictors of body mass index and associations with cardiovascular risk factors in Australian children: a prospective cohort study

Objective: To examine predictors of body mass index (BMI) at the age of 8 y in a prospective study of Australian children. Design: Longitudinal survey of a cohort of Australian children followed from the 16th week of gestation to 8 y. Subjects: In total, 741 boys and 689 girls who attended the survey as 8 y olds. Measurements: Weight and height, blood pressure measured by automated oscillometry, fasting blood lipids and glucose. Questionnaire assessment of activity and diet. Results: Proportions of overweight including obesity in boys and girls were, respectively, 22 and 25% at 1 y, 14 and 14% at 3 y, 13 and 18% at 5 y and 15 and 20% at 8 y. At the age of 1, 3, 6 and 8 y, children with overweight including obesity showed significantly more adverse cardiovascular risk factors. Blood pressure ( BP) was significantly higher by 2/3 mmHg (systolic/diastolic) at 1 y, 3/2 mmHg at 3 y, 4/2 mmHg at 5 y and 6/2 mmHg at 8 y; HDL was significantly lower (P=0.002) by 8% and triglycerides were significantly higher by 27% (P<0.001). In multivariate regression, BMI at the age of 8 y was significantly predicted positively by birth weight, mother's BMI and hours spent in watching television at the time of the survey of 6 y olds. Mothers being ex-smokers or non smokers and children being 'slightly active' and 'active' negatively predicted BMI in 8 y olds. In a subset of 298 children with information about fathers, paternal BMI was an additional independent predictor. Maternal or paternal overweight including obesity each independently increased risk of overweight including obesity at the age of 8 y three- fold. A food factor with consumption of cereals and breads as the major components derived from a Food Frequency Questionnaire in a subset of 340 children was also an independent negative predictor of BMI in multivariate models. Conclusion: The increasing rate of overweight including obesity, particularly in girls, is associated with an increase in cardiovascular risk factors very early in life. Improvement of health-related behaviours within the family and a focus on promotion of activity in children should be priorities in achieving weight control.