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Dr. McIvor is Associate Professor of Medicine, Dalhousie University, and Staff Respirologist, Queen Elizabeth II Health Sciences Centre.
Correspondence to: R. Andrew McIvor, MD, MSc, Staff Respirologist, Queen Elizabeth II Health Sciences Centre, 1796 Summer St, Room 4479, Halifax, Nova Scotia, Canada B3H 3A7; e-mail: amcivor{at}is.dal.ca
Although environmental factors are clearly important determinants of asthma, numerous studies have revealed that asthma also has strong genetic components. The genetic answer to the asthma conundrum is unlikely to be simple, as multiple regions of the human genome are likely to contain susceptibility genes for asthma.
In this issue of CHEST (see page 1474), Barr et al report that activity status and obesity might modify the influence of genetic polymorphisms on patients with adult-onset asthma. They suggest the presence of Gly16 allele is associated with adult-onset asthma in sedentary women, implying that the relationship between ß2-adrenoceptor polymorphisms in adult-onset asthma is modifiable by environmental factors. This group has recently shown that a similar gene environment interaction may exist between ß2-adrenoceptor polymorphisms and smoking.1
Previous analyses of genetic risks of asthma have not been stratified by activity status. Barr et al used a nested case-control study design, recruiting individuals from the ongoing Nurses’ Health Study in the United States. Weight, activity status, and height were self-reported. Caloric intake was calculated from the validated questionnaire.
The study suggests that sedentary lifestyle, which the authors defined very conservatively (as a woman who walked < 1 h/wk at a brisk pace), unmasks a genetic risk for asthma in addition to contributing to obesity-related asthma. Even though this study design is only hypothesis-generating, it may suggest a very important public health message that has been highlighted and investigated by our cardiology colleagues,2 who have shown that a sedentary lifestyle is an independent risk factor for coronary heart disease and stroke, and that regular exercise has a significant place in secondary prevention of these conditions.
Despite the recognition of the scientific community of the importance of exercise, little is known about the epidemiology of exercise, particularly in patients with obstructive lung disease. Chen et al3 examined energy expenditure on leisure activities in 16,813 individuals who took part in the Canadian National Population Health Survey; although Chen et al were not able to explain a positive association between lack of physical activity, obesity, and a diagnosis of asthma self-reported by patients, they did show reduced activity in the older populations especially women.
Stressing the importance of activity as a general health measure
in all individuals was recently addressed. A consensus
statement4
from the Centers for Disease Control and
Prevention was developed in 1995 to encourage increased participation
in physical activity in Americans of all ages. This group issued a
public health statement recommending the type and amount of physical
activity needed for health promotion and disease prevention. They
suggest that every US adult should accumulate 
30 min of
moderate-intensity physical activity on most, preferably all, days of
the week. As part of an "ABC" of sports medicine published in the
British Medical Journal,2
more precise
suggestions were delivered.
Women should walk 2 miles in < 30 min at least 3 d/wk, and men should walk 2 miles in < 27 min, at least 3 d/wk. Other options are 2 miles in 30 to 40 min 6 d/wk, or a total of 2 miles (3 km) each day in three periods of 10 min.
Therefore, despite any limitation of the study design or generalizability of the results, this study opens an exciting simple cost-effective lifestyle modification that should be further explored. Activity level and body mass index should be recorded in future genetic studies. Other researchers may be able to address this issue from long-term epidemiologic birth cohorts.
The advice for women, in particular, to avoid the sedentary lifestyle, is an extremely good public health message and in keeping with overall health promotion. In persons with asthma or family members of patients with asthma, we should encourage frequent exercise in accordance with their capabilities, physical limitations, and personal interests.
References
This article has been cited by other articles:
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  S. D. Aaron, D. Fergusson, R. Dent, Y. Chen, K. L. Vandemheen, and R. E. Dales Effect of Weight Reduction on Respiratory Function and Airway Reactivity in Obese Women Chest, June 1, 2004; 125(6): 2046 - 2052. [Abstract] [Full Text] [PDF]
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