Background: Epidemiological studies suggest that a diet high in marine fatty acids (fish oil) may have beneficial effects on inflammatory conditions such as rheumatoid arthritis and possibly asthma.
Objectives: 1. To determine the effect of marine n-3 fatty acid (fish oil) supplementation in asthma. 2. To determine the effect of a diet high in fish oil in asthma.
Search strategy: The Cochrane Airways Review Group register was searched using the terms: marine fatty acids OR diet OR nutrition OR fish oil OR eicosapentaenoic acid OR EPA. Bibliographies of retrieved trials were searched and fish oil manufacturers contacted.
Selection criteria: Randomised controlled trials in patients with asthma more than two years of age were included. The study duration had to be in excess of four weeks. Double blind trials were preferred, but single-blind and open trials were also reviewed for possible inclusion. Three reviewers read each paper, blind to its identity. Decisions concerning inclusion were made by simple majority. Quality assessment was performed by all three reviewers independently.
Data collection and analysis: The only comparison possible was between marine n-3 fatty acid supplementation and placebo. There were insufficient trials to examine dietary manipulation alone.
Main results: Nine randomised controlled trials conducted between 1986 and 2001 satisfied the inclusion criteria. Seven were of parallel design and two were cross-over studies. Eight compared fish oil with placebo whilst one compared high dose vs low dose marine n-3 fatty acid supplementation. Two studies were conducted in children, whilst the remaining seven studies were conducted in adults. None of the included studies reported asthma exacerbations, health status or hospital admissions. There was no consistent effect on any of the analysable outcomes: FEV1, peak flow rate, asthma symptoms, asthma medication use or bronchial hyper reactivity. One of the studies performed in children which combined dietary manipulation with fish oil supplementation showed improved peak flow and reduced asthma medication use. There were no adverse events associated with fish oil supplements.
Reviewer's conclusions: There is little evidence to recommend that people with asthma supplement or modify their dietary intake of marine n-3 fatty acids (fish oil) in order to improve their asthma control. Equally, there is no evidence that they are at risk if they do so.