Effect of Dietary Supplements With Fish Oil on Mannitol-induced Airway Sensitivity & Inflammation in Persons With Asthma

Asthma is a chronic inflammatory disorder of the airways characterized by recurrent episodes of dyspnea, wheeze and chest tightness and is associated with variable airway obstruction. Exercise-induced bronchoconstriction (EIB) is a feature specific to asthma. Exercise testing protocols have been developed to identify the presence of asthma as well as to assess asthma therapy. Airway narrowing following exercise in persons with asthma is thought to result from dry air hyperpnoea-induced dehydration of the airway surface, leading to the release of mediators from inflammatory cells residing in the airway. Regular treatment with inhaled corticosteroids inhibits the airway response to exercise by decreasing the number of inflammatory cells and thus the source of bronchoconstricting mediators. Therefore, a decrease in the source of mediator may be the reason for this eventual inhibition of the airway response to exercise. It has recently been demonstrated that fish oil supplementation in capsule form, taken daily over three weeks, provides significant protection against EIB. This protection appears to be of equal or greater efficacy than inhaled corticosteroids treatment over a similar period. This may have positive implications in the treatment of asthma as inhaled corticosteroids are known to have some unwanted side effects. Fish oil supplementation in the high doses given in previous studies have not demonstrated any side effects and may lead to an alternative treatment, or a decrease in the dose of inhaled steroids required in the treatment of asthma. A new bronchial provocation test using inhaled mannitol, derived from the mechanism of EIB, has been recently developed and is now registered in Australia and the European Union. Mannitol causes airway narrowing in a similar manner to exercise in persons with asthma and is effective in identifying responsiveness to inhaled corticosteroids. We wish to use inhaled mannitol as a model for EIB in an effort to further investigate the use of fish oil supplementation in the treatment of asthma. Our hypothesis is that daily orally administered encapsulated fish oil will attenuate the airway response to mannitol over a 3-week treatment period. We also wish to measure associated markers of inflammation in the blood, urine, sputum and exhaled condensate as well as monitor clinical outcomes such as symptoms and daily beta2 agonist use.