Objectively Measured Physical Activity Levels and Obesity. A Study with ISCOLE Portuguese Children

Background: The effects of physical activity (PA) in producing weight loss are well known. However, there is some controversy about the relationship between PA intensity and levels of obesity in children. Further, different cut-offs have been used to classify obesity, which may influence the observed associations with PA. The International Study of Childhood Obesity, Lifestyle, and the Environment (ISCOLE) aims to determine the relationship between lifestyle characteristics and obesity in children, and to investigate the influence of behavioural settings and physical, social and policy environments on the observed relationships within and between countries.

Purpose: To analyze the importance of different PA levels in overweight and obesity as classified by CDC and IOTF in Portuguese ISCOLE children.

Methods: Six hundred and twenty-five Portuguese children aged 10 years (boys=272; girls=373) were monitored during seven consecutive days for their physical activity levels using the Actigraph GT3X+ accelerometer. Treuth cut-offs were used to classify vigorous (VPA), moderate (MPA), light (LPA) activities and sedentarism (SED) in minutes per day. Body mass index (BMI) was calculated as kg/m2. Multinomial logistic regression analyses were used in SPSS 20.

Results: : Obesity and overweight prevalences were 8.2% (boys: 10.1%; girls: 6.9%) and 27.2% (boys: 29.1%; girls: 27.0%), and 14.5% (boys:17.3%; girls:12.5%) and 22.7% (boys:25.4%; girls:21.6%), as assessed by IOTF and CDC, respectively. Boys had 2.3 (95% CI =1.2-4.2, p=0.009) and 2.2 (95% CI=1.3-3.6, p=0.002) higher odds of being obese than girls using IOTF and CDC criteria, respectively. Independently of gender, VPA significantly reduced the odds of being overweight using IOTF (OR=0.87; CI95% =0.84-0.98, p=0.014) and CDC criteria (OR=0.91; CI95% =0.80-0.96, p=0.005), but not of being obese. Sedentarism, light and moderate activities have no influence in weight categories whatever the definition used.

Conclusions: Time spent in vigorous activities is associated with overweight in Portuguese children, irrespective of the overweight definition used. At 10 years of age, Portuguese boys have higher odds of being obese than girls.