Objective: Low physical activity and high sedentary behavior are associated with adverse health outcomes, including asthma. The purposes were to (1) determine if low physical activity and/or high screen time increase the risk of asthma and airway hyperresponsiveness (AHR) in youth and (2) determine if weight status modifies these associations.
Methods: This is a prospective cohort study of healthy weight and overweight Canadian youth. In 2003-2005, 723 youth (8.6 ± 0.5 years; 34.0% asthma, 55.9% boys) were recruited from the 1995 Manitoba Prospective Cohort Study. In 2008-2010, 489 returned for follow-up measures (30.9% asthma, 56.6% boys). The primary exposure variables were parent-reported physical activity and screen time at 8-10 years of age. The primary outcome measures were pediatric allergist-defined asthma and AHR defined as the provocative concentration of methacholine required to induce a 20% fall in forced expiratory volume in 1 second (FEV(1)).
Results: Low physical activity (≤2 times weekly) was not associated with asthma or AHR. However, high screen time (≥1 hour/day) was associated with a greater odds of asthma at baseline (odds ratio (OR) = 2.01, 95% confidence interval (CI) = 1.20-3.37, p < .01) and follow-up (OR = 2.11, 95% CI = 1.14-3.89, p < .02) versus low screen time. This association was more pronounced among overweight youth (baseline: OR = 3.95, 95% CI = 1.70-9.12, p < .0001; follow-up: OR = 3.22, 95% CI = 1.17-8.86, p < .02). Screen time was not associated with AHR at baseline or follow-up.
Conclusions: High screen time increases the risk of asthma, particularly among overweight youth. Screen time, in addition to physical activity, should be included in clinical assessments of youth with asthma.