(08-04-06) Fish Oil Improves Lung Function in Exercise-Induced Asthma

Most people with asthma experience breathing difficulties in response to cold or exercise. These environmental conditions trigger inflammatory responses and airway narrowing along with wheezing, cough, and chest tightness. Symptoms result because of the chronic inflammation and constricted airway passages characteristic of asthma. It may be that the deep rapid breathing that accompanies exercise-induced asthma triggers water loss in the airways, which then provokes inflammatory responses. Because of their anti-inflammatory effects in respiratory tissue, long-chain omega-3 polyunsaturated fatty acids (n-3 LC-PUFAs) may ease these responses and reduce airway narrowing. Only a few controlled intervention studies have been conducted in asthmatics. Some have reported positive effects with n-3 LC-PUFAs in children, alpha-linolenic acid-rich perilla oil in adults, and green-lipped mussel lipid extract in adults, but others found no benefits or changes in airway responsiveness. This literature was reviewed recently.

Timothy Mickleborough and colleagues at the Indiana University School of Medicine, USA, whose report of significant benefits of n-3 LC-PUFAs in elite athletes with exercise-induced bronchoconstriction appeared previously in the PUFA Newsletter, investigated the effects of n-3 LC-PUFAs on breathing performance in patients with asthma. Here, the Mickleborough team examined the effect of similar amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in asthmatic adults following exercise.

In this randomized, placebo-controlled crossover study, 16 asthmatic patients currently using bronchodilators were randomly assigned to consume 3 gm EPA and 2 gm DHA/day from fish oil or an olive oil placebo with meals for 3 weeks. No group of non-asthmatic people was included because n-3 LC-PUFAs do not appreciably affect pulmonary function or inflammatory mediators in healthy people. After a 2-week washout period, patients were switched to the alternative supplement for another 3 weeks. At baseline and after 3 weeks, pulmonary function was assessed by treadmill exercise-induced forced expiratory volume (FEV) before exercise and at 1, 5, 10, 15, 30, 45, and 60 minutes thereafter. Blood samples were taken before exercise and 15 and 60 minutes after, and sputum induced 48 hours prior to exercise and at 1 hour and 24 hours later. Leukotrienes B4 and B5 and other inflammatory mediators (cytokines) were measured in venous blood white cells (PMNL) and sputum and fatty acids measured in neutrophils. All participants recorded their use of inhaled bronchodilators during the study.

Those on the normal and placebo diets experienced a 22% and 21% decrease in FEV, respectively, while FEV in those consuming fish oil declined by 8%, an amount below the threshold diagnosis for exercise-induced bronchoconstriction.

Figure 1. Percentage change in forced expiry volume before and after exercise in asthmatic patients consuming normal, placebo or fish oil diets. Comparisons at each time period among diets differ significantly between different letters (P<0.05). Reproduced by kind permission of Chest.

Differences between the fish oil diet and placebo or normal diet were significant within one minute after exercise and were sustained for an hour thereafter (P<0.05). Other measures of pulmonary function, such as forced maximal expiration showed significant differences with fish oil similar to those in FEV.

Consumption of fish oil was accompanied by a significant reduction in sputum eosinophils and neutrophils (different types of white blood cell) before exercise and at 1 hour and 24 hours after, while macrophages were increased at these times. Concentrations of esoinophils and neutrophils were positively correlated with the severity of the exercise-induced bronchoconstriction as reflected in the change in FEV. These responses are consistent with reduced immune responses. Inflammatory mediators?leukotrienes C4 and E4, tumor necrosis factor-alpha, interleukin-1beta, prostaglandin D2?were also significantly reduced in sputum at the same times of observation. In blood, fish oil supplementation significantly reduced proinflammatory leukotriene B4 produced from lymphocytes (PMNLs) and increased the production of the anti-inflammatory leukotriene B5, generated from EPA when compared with the placebo diet and measured before exercise. These changes are consistent with what would be expected when inflammatory responses are suppressed by fish oil.

This study demonstrated pronounced improvements in pulmonary function after exercise-induced airway constriction in asthmatic patients who consumed fish oil. Loss in forced expiry volume that occurs following exercise in nearly all asthmatic patients was significantly lower by 64% and use of inhaled bronchodilators was reduced by 31%. In addition, dietary fish oil reduced airway inflammation, bronchoconstriction, and the altered breathing pattern observed in exercise-induced asthma. However, the contrast between these findings and the lack of improvement with fish oil in patients with mild asthma observed by others warrants further investigation. Mickleborough?s team suggested that exercise conditions with dry cold air and intense activity might be required to observe exercise-induced airway narrowing. It sounds as though the ski slopes would be an ideal place to confirm these promising findings.
Mickleborough TD, Lindley MR, Ionescu AA, Fly AD. Protective effect of fish oil supplementation on exercise-induced bronchoconstriction in asthma. Chest 2005;60:1-6.

Mickleborough TD, Rundell KW. Dietary polyunsaturated fatty acids in asthma- and exercise-induced bronchoconstriction. Eur J Clin Nutr 2006;83:187-188.

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