Paediatric asthma and obesity

Summary

None of the explanations proposed for the increase in paediatric asthma have been adequate. It is becoming apparent that the cause of the increase in asthma must be multi-factorial. Increasing attention has been focused on the role of lifestyle in the development of asthma. Lifestyle changes that have occurred in children are those in diet and decreased physical activity, with obesity being the product of these changes. The increase in asthma, obesity and a sedentary lifestyle have occurred together. However, a temporal relationship between asthma, obesity and decreased physical activity has not been determined in the paediatric literature. Limited data suggest that decreased physical activity could be playing a role in the aetiology of asthma independent of obesity. Furthermore, there has been substantial research on the benefits of exercise programmes for paediatric patients with asthma. Longitudinal trials monitoring physical activity, obesity and the development of asthma are needed.

Introduction

Asthma is the most common chronic illness in childhood. Its prevalence, severity and hospitalisation rates have increased significantly in developed countries over the last four decades. Many explanations have been postulated but none have explained this increase convincingly. The cause of the increase in asthma must be multi-factorial, with allergen sensitisation, lifestyle and genetics emerging as primary determinants.¹ There is consistent evidence that aeroallergen sensitisation plays a significant role in the development of asthma.² Also, it is well established that a family history of atopy is a major risk factor. On the other hand, the hygiene hypothesis has also received a lot of attention. This is the idea that decreased exposure to bacterial products secondary to increased hygiene and antibiotic use is responsible for increased Th2 response associated with asthma. This hypothesis does not seem to be fully sufficient given that most of the major improvements in hygiene far preceded the increase in asthma. Finally, increasing attention has been focused on the role of lifestyle change in the development of asthma. Obvious lifestyle changes that have occurred over the last four decades are those in diet and decreased physical activity, with obesity being the product of these changes.

The incidences of asthma and obesity in childhood have increased in parallel over the last four decades. The prevalence of childhood obesity in the USA, for instance, increased by 100% between 1980 and 1994.³ The level of physical activity in children is also at an ‘all-time low’ in most industrialised nations, primarily due to the advent of television, computers and the Internet. Does breathlessness associated with asthma lead to decreased physical activity, increased indoor allergen exposure and subsequent obesity, or does decreased physical activity lead to the development of asthma through mechanical and molecular mechanisms independent of obesity? Does obesity precede asthma and create an inflammatory micro-environment that fosters the development of asthma? Whether obesity is responsible for the increased incidence of asthma is still controversial. Determining the temporal association between asthma, obesity and decreased physical activity will be essential to answering these questions. The associations between asthma and obesity in the adult population have been modest, with relative risks ranging from 1.5 to 3 (compared with five- to 10-fold increased risk of cancer with cigarette smoking).⁴ This article will review the paediatric literature on lifestyle changes (namely obesity and physical activity) and the evidence about the impact on the aetiology and severity of asthma. Also, a case will be made for an exercise prescription being incorporated into the management of all paediatric patients with asthma.