Body mass index, clusters of health behaviour among school-age children and young people in Sweden

Because habits learnt as children, both good and bad, tend to stick with people throughout their lives, childhood is an important period not only for physical and mental development but also for the development of healthy lifestyles. According to the World Health Organization, a healthy lifestyle includes daily physical activity, a healthy diet, decreased inactivity, a normal body mass index (BMI) and a non-smoking environment (World Health Organisation [WHO], 2017). In Sweden, the vast majority of children and young people are healthy and engage in healthy lifestyles, as shown in health behaviours measured among them that continue to improve with age (WHO, 2018).

Even so, the physical activity of Sweden's children and young people has room for improvement. The WHO recommends that children and young people to be moderately physically active for at least 1 hour per day, ideally by engaging in physically strenuous, cardio-intensive activities, and to engage in activities that strengthen the body at least three times per week (2010a). Being physically active can involve walking or cycling to school, engaging in various forms of sport, participating in activities at school or playing with friends. Physical activity confers numerous health benefits for school-age children and adolescents in terms of fitness, muscle strength, blood pressure, blood fat, bone density and BMI, with effects both in the short term and into adulthood (Strong et al, 2005; Janssen and LeBlanc 2010; Ekblom-Bak et al, 2018). Physical activity is also likely to improve the development of cognitive functions (Herting and Chu, 2017) and contribute to quality of life and psychological health (Hallal et al, 2006; Wu et al, 2017). However, according to the WHO (2010b), 81% of school-age children and young people in the world move too little and spend many of their waking hours engaging in sedentary activities instead, often ones involving screens (LeBlanc et al, 2015; Bucksch et al, 2016). In particular, physical activity and outdoor play decrease with age, and girls have tended to demonstrate lower levels of activity than boys (Pagels et al, 2014; Elinder et al, 2014).