Active Lifestyle: The Next “Smoking Cessation”?
Authors: Anne E. Dixon, Benjamin T. Suratt
Journal: American Journal of Respiratory and Critical Care Medicine (2014)

Obesity is a global epidemic, not simply a disease of the Western world (1), and this has grave implications for lung health. There is a growing appreciation that obesity is associated with asthma, but the study by Chen and colleagues (pp. 1194–1203) in this issue of the Journal drives home some particularly salient features of this epidemic, which are worthy of attention from clinicians and policymakers alike (2).

Chen and colleagues present results of a study of 2,758 Taiwanese children, in which they examined the relationship between asthma, obesity, physical fitness, and sedentary time. The investigators enrolled fourth grade school children and followed them over 3 years with systematic annual evaluations for lung disease and measures of obesity. The approach taken, with multiple anthropomorphic measures and systematic annual follow-up, provides confidence in their conclusions. Central obesity, among measures of adiposity, was most strongly associated with the presence of asthma in their cohort. Of particular interest, they show data suggesting that low physical fitness and high “screen time” (television/video games) lead to central obesity, which appears to alter lung function as measured by FEV1/FVC. Physical inactivity is likely to be an important, perhaps modifiable, risk factor for the development of asthma in children.

Central obesity was particularly associated with active asthma. This is a finding that is now gaining some traction in the literature, as many investigators have variously reported that central obesity is a risk factor for low lung function (3) and for the development of incident asthma (4). Central obesity clearly has mechanical effects on the thoracic cavity, and so it is perhaps self-evident that central obesity could lead to low lung volumes. Breathing at low lung volumes in normal human volunteers can induce airway reactivity (5), and may therefore contribute to the development of asthma, particularly in those with central obesity, but this is unlikely to be the whole story; airway reactivity in animal models appears not to be related to low lung volumes (6). Thus, other factors must be at play. Central obesity is produced by deposition of visceral adipose tissue, and this form of adipose tissue is far more pathogenic in terms of producing proinflammatory mediators and is more closely related to the metabolic complications of obesity than subcutaneous adipose tissue (7, 8). We have previously found that inflammation in visceral adipose tissue is associated with asthma in obesity (9). Mediators produced in abundance by visceral adipose tissue could have direct effects on the airways, or perhaps produce changes in immune responses that predispose to the development of asthma in obesity.

How central obesity is related to asthma is an important scientific question that will require much additional study to understand, but there are immediate clinical implications of the current study in which central obesity was strongly associated with low physical activity and high screen time. This is an all-too-common scenario, as increasing numbers of children (and adults) all over the world live in urban environments with sedentary lifestyles and limited access to physically active recreational opportunities. Addressing this lifestyle issue is clearly one of the most pressing public health issues of our time. Pulmonologists have long focused on public health issues, such as smoking; obesity is now the pressing pandemic that needs our urgent attention. This study provides important scientific and clinical insights that suggest we need to pay far more attention to the role of ubiquitous modern lifestyle factors and the role that these factors play in the development of lung disease.

Solving the obesity pandemic is clearly a challenge for the 21st century, but there are likely to be interventions that can be promoted during routine medical care. Those caring for patients with asthma routinely counsel patients about smoke and other environmental exposures. It is now time to start focusing on lifestyle factors such as diet and exercise as major modifiable risk factors contributing to their disease. This is likely to be particularly important for patients who are overweight, as a growing body of evidence suggests that obese patients with asthma do not respond as well to steroid controller therapy as lean patients, and tend to have more poorly controlled asthma (10). Promoting lifestyle changes may be particularly challenging in those with asthma, as patients with asthma may experience greater symptoms with physical activity, and so have more difficulty undertaking regular exercise. There are a few small studies that suggest that successful weight loss can be achieved in individuals with asthma through lifestyle modification, and this weight loss is associated with improvements in asthma control (11–13). By focusing on prevention of obesity in children, we are likely to prevent the development of a lifelong disorder that will produce lifelong pulmonary morbidity. Clinicians need to incorporate lifestyle counseling into the routine care of patients with asthma, and there is a pressing need to develop systematic lifestyle interventions that will work in this challenging patient population.