Full article: http://www.medscape.com/viewarticle/556355?src=mp

Exercise May Reduce Risk for Bronchial Hyperresponsiveness

News Author: Will Boggs, MD
CME Author: Charles Vega, MD

May 11, 2007 — Even a few hours of exercise a week is associated with reduced
risk of bronchial hyperresponsiveness (BHR), according to a report in the May
issue of Thorax.

"You do not need to exercise a lot to gain a beneficial effect for your
breathing, as we found a protective effect even for a rather low level of
activity," Dr. Bénédicte Leynaert from Faculté de Médecine Xavier Bichat, Paris,
France told Reuters Health.

Dr. Leynaert and colleagues investigated the association between usual levels of
physical activity and BHR in more than 5000 adults participating in the European
Community Respiratory Health Survey II.

Nearly two-thirds (60.0%) of the population exercised to breathlessness no more
than once a week, 26.5% exercised 2-3 times a week, and 13.5% exercised
regularly at least 4 times a week, the results indicate.

Only 16.1% of the group exercised at least 4 hours per week, while most
exercised 1-3 hours per week (42.4%) or less than an hour per week (41.5%).

BHR was inversely related to both the frequency and the duration of physical
exercise, the investigators report. The prevalence of BHR ranged from 10.9%
among those exercising at least 4 times a week to 11.6% for those exercising 2-3
times a week and 14.5% for those exercising once a week or less.

Similarly, BHR prevalence was 10.7% for those exercising at least 4 hours per
week, 10.9% for those exercising 1-3 hours per week, but significantly higher at
15.9% for those exercising less than 1 hour per week, the report indicates.

These patterns were similar regardless of gender, body-mass index, cigarette
smoking behavior, and atopic classification, the researchers note.

"Physical activity might influence airway physiology and BHR," the investigators
speculate. "Another possible explanation is that moderate physical activity
might be associated with a reduction in systemic inflammation."

"One of the particularities of this study is that it is population-based, and
the results might be applied to anyone, which is rarely the case when studies
are run either in a clinical setting or in specific groups of subjects (such as
athletes)," Dr. Leynaert pointed out.

"Further data are needed to clarify the relationship between physical activity
and BHR and to determine the optimal amount (frequency and duration) and type of
physical activity required," he and his colleagues conclude. "If confirmed, our
results may contribute to the development of primary prevention programs for
pulmonary diseases."

"An interesting question" that arises from this study is "What is the
cause-effect relationship?" writes Dr. Donald A. Mahler from Dartmouth-Hitchcock
Medical Center, Lebanon, New Hampshire in a related editorial. He believes it
plausible that exercise decreases BHR through an anti-inflammatory effect.

"Although additional studies are needed," the editorial concludes, "a randomized
controlled trial with physical activity as the intervention and markers of
airway inflammation together with prevention or modification of BHR as outcomes
is probably not feasible or realistic."

Thorax. 2007;62:376, 403-410.

Reuters Health Information 2007. © 2007 Reuters Ltd.
Clinical Context

Current public health recommendations advise regular exercise to prevent a
variety of chronic diseases, but the role of exercise in the development of BHR
and asthma is not entirely clear. The authors of the current study reviewed the
literature regarding this subject and found that physical activity had been
demonstrated to reduce BHR among children with asthma, but not in children
without asthma. Physical fitness during childhood has been suggested to reduce
the risk for adolescent asthma, and a study of twins demonstrated that exercise
could reduce the risk of developing asthma.

At the same time, it is fairly well established that intense exercise increases
BHR through a number of mechanisms. Whereas these studies focused on athletes,
the current cross-sectional research focuses on the general adult population.
Study Highlights

* Study participants were derived from the European Community Respiratory
Health Survey II, which enrolled adults from 11 countries during the years 1998
to 2002. All subjects answered a baseline questionnaire with a focus on
pulmonary history and risk factors for lung disease. Frequency and duration of
physical activity were also assessed.
* Lung function was measured by forced expiratory volume in 1 second (FEV1)
and maximum forced vital capacity. Patients without a significantly reduced FEV1
went on to receive methacholine challenge testing with a maximum dose of 2 mg of
methacholine. Finally, subjects were also assessed for total IgE levels along
with IgE levels for particular antigens.
* The main study outcome was the relationship between BHR and the duration
and frequency of reported exercise. BHR was defined by a decrease in FEV1 of at
least 20% during methacholine challenge testing. This result was adjusted for
sex, age, body mass index, smoking status, IgE levels, family history of asthma,
and both asthma symptoms and asthma diagnosis.
* 5158 participants completed the study requirements. 80% of the study
cohort was younger than 50 years, and 43.6% of subjects had never smoked
cigarettes. Slightly less than 5% of participants reported a current diagnosis
of asthma.
* 60% of the study cohort exercised to breathlessness either once per week
or less than once per week, while 26.5% and 13.5% of subjects exercised 2 to 3
times or 4 or more times per week, respectively. 41.5%, 42.4%, and 16.1% of
participants reported exercise duration of less than 1 hour, 1 to 3 hours, or 4
or more hours per week.
* The prevalence of BHR was 13%, and it was more common among patients with
obesity, atopy, asthma, or a family history of asthma.
* BHR was negatively correlated with the frequency of physical activity,
being present in 14.5%, 11.6%, and 10.9% of participants reporting exercise once
a week or less, 2 to 3 times per week, or 4 or more times per week,
respectively. The corresponding adjusted odds ratios for BHR were 1.00, 0.78,
and 0.69, respectively.
* The prevalence of BHR also decreased with increasing duration of
exercise. 15.9%, 10.9%, and 10.7% of subjects reporting exercise duration of
less than 1 hour, 1 to 3 hours, or 4 or more hours per week, respectively, had
evidence of BHR. The respective adjusted odds ratios for this outcome were 1.00,
0.70, and 0.67.
* Participants who reported exercising 2 or more times per week and
exercising for 1 or more hours per week had an adjusted odds ratio of 0.74 for
BHR vs other, less active subjects. This reduction in the risk for BHR was
statistically significant.
* The salutary effects of exercise on BHR was noted in all participant
subgroups, including analyses based on sex, body mass index, smoking status, and
the absence of asthma and asthma symptoms.

Pearls for Practice

* Previous research has suggested that physical activity reduces BHR in
children with asthma and that children who exercise may have a lower risk of
developing asthma. However, intense exercise in athletes has been demonstrated
to increase BHR.
* The current study demonstrates that both increased frequency and duration
of physical activity are associated with a reduced prevalence of BHR in adults,
regardless of sex, body mass index, smoking status, or the absence of asthma.