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3.3.2 AIR POLLUTION
Challenge studies demonstrate that various pollutants can enhance the response of patients with
asthma to allergen inhalation. 198,199 Time-series studies suggest that air pollution may provoke
acute asthma attacks or aggravate existing chronic asthma although the effects are very much
less than those with infection or allergen exposure. 200,201 While it might seem likely that moving
from a highly polluted environment might help, in the UK, asthma is more prevalent in 12-14
year olds in non-metropolitan rather than metropolitan areas. 202 Much less attention has been
focused on indoor pollutants in relation to asthma and more work is required. 203,204
3.3.3 IMMUNOTHERAPy
subcutaneous immunotherapy
Trials of allergen specific immunotherapy by subcutaneous injection of increasing doses of
allergen extracts have consistently demonstrated beneficial effects compared with placebo in the
management of allergic asthma. Allergens included house dust mite, grass pollen, tree pollen, cat
and dog allergen and moulds. Cochrane reviews have concluded that immunotherapy reduces
asthma symptoms, the use of asthma medications and improves bronchial hyper-reactivity. The
most recent review included 36 trials with house dust mite, 20 with pollen, 10 with animal
allergens, two with cladosporium mould, one with latex and six with multiple allergens. 205
Evidence comparing the roles of immunotherapy and pharmacotherapy in the management of
asthma is lacking. One study directly compared allergen immunotherapy with inhaled steroids
and found that symptoms and lung function improved more rapidly in the group on inhaled
steroids. 206 Further comparative studies are required.
Immunotherapy for allergic rhinitis has been shown to have a carry over effect after therapy
has stopped. 207
B immunotherapy can be considered in patients with asthma where a clinically
significant allergen cannot be avoided. The potential for severe allergic reactions to
the therapy must be fully discussed with patients.
sublingual immunotherapy
There has been increasing interest in the use of sublingual immunotherapy, which is associated
with far fewer adverse reactions than subcutaneous immunotherapy. A systematic review
suggested there were some benefits for asthma control but the magnitude of the effect was
small. 208 Further randomised controlled trials are required.
B sublingual immunotherapy cannot currently be recommended for the treatment of
asthma in routine practice.
3.4 dietAry MAniPulAtion
3.4.1 ELECTROLyTES
3 non-PhArMAColoGiCAl MAnAGeMent
Increasing dietary sodium has been implicated in the geographical variations in asthma mortality 209
and high sodium intake is associated with increased bronchial hyper-responsiveness. 210,211 A
systematic review of intervention studies reducing salt intake identified only minimal effects
and concluded that dietary salt reduction could not be recommended in the management of
asthma. 212 Low magnesium intakes have been associated with a higher prevalence of asthma
with increasing intake resulting in reduced bronchial hyper-responsiveness and higher lung
function. 213 Magnesium plays a beneficial role in the treatment of asthma through bronchial
smooth muscle relaxation, leading to the use of intravenous or inhaled preparations of
magnesium sulphate for acute exacerbations of asthma. 214 Studies of oral supplementation are
limited and more trials are required. 215-217
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