Physical activity and asthma development in childhood: Prospective birth cohort study.

BACKGROUND: Sedentary behavior and decreased physical activity are possible risk factors for developing asthma. This longitudinal study investigates the association between physical activity and subsequent asthma. We hypothesize that children with decreased physical activity at early school age, have higher risk of developing asthma. METHODS: One thousand eight hundred thirty-eight children from the KOALA Birth Cohort Study were analyzed. Children who were born prematurely or with congenital defects/diseases with possible influence on either physical activity or respiratory symptoms were excluded. Physical activity, sedentary behavior, and screen time were measured at age 4 to 5 years by questionnaire and accelerometry in a subgroup (n = 301). Primary outcome was asthma, assessed by repeated ISAAC questionnaires between age 6 and 10. Secondary outcome was lung function measured by spirometry in a subgroup (n = 485, accelerometry subgroup n = 62) (forced expiratory volume in 1 second [FEV1], forced vital capacity [FVC] and FEV1/FVC ratio) at age 6 to 7 years. RESULTS: Reported physical activity was not associated with reported asthma nor lung function. Accelerometry data showed that daily being 1 hour less physically active was associated with a lower FEV1/FVC (z score beta, -0.65; 95% confidence interval, -1.06 to -0.24). CONCLUSIONS: Physical activity at early school age was not associated with reported asthma development later in life. However, lung function results showed that sedentary activity time was associated with lower FEV1/FVC later in childhood. As this is the first longitudinal study with objectively measured physical activity and lung function, and because the subgroup sample size was small, this result needs replication