Affiliations: Halifax, Nova Scotia, Canada
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: email@example.com
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 betweenβ
2-adrenoceptor polymorphisms in adult-onset
asthma is modifiable by environmental factors. This group has recently
shown that a similar gene environment interaction may exist betweenβ
2-adrenoceptor polymorphisms and
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.
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