Vol.4 Issue 1
Asthma

In recent months, I've fielded questions from many asthmatic patients regarding the efficacy of fish oil to prevent or manage asthma attacks. What's the current evidence on fish oil supplementation in persons with asthma?

Fish oil has been touted as a treatment for a wide range of inflammatory conditions. The anti-inflammatory constituent of fish oil is eicosapentaenoic acid (EPA), a long chain n-3 polyunsaturated fatty acid. EPA competes with arachidonic acid (AA) in cyclooxygenase and lipoxygenase pathways and prevents the generation of inflammatory mediators associated with AA metabolism.

A recent systematic review by the Cochrane group concluded that there is no evidence to support the efficacy of n-3 fatty acid supplements to reduce asthma medication usage, or to improve asthma symptoms, bronchial hyperreactivity, or FEV1 (1). This finding may seem surprising given the fact that n-3 fatty acid supplementation has been associated with improvements in other inflammatory conditions, such as rheumatoid arthritis, cystic fibrosis, and psoriasis. However, these conditions are characterized by neutrophilic inflammation, and neutrophils seem to be highly sensitive to the effects of n-3 fatty acids. In contrast, eosinophils and mast cells are the effector cells involved in asthma, and in vitro studies suggest that they are not susceptible to the anti-inflammatory effects of n-3 fatty acids (1). Because the studies that were reviewed tested the effects of fish oil, no conclusions can be drawn about the efficacy of increasing whole fish intake to manage asthma.

A recent study suggests that n-6 fatty acids might be harmful for persons with asthma. n-6 fatty acids are essential polyunsaturated fatty acids that are found in vegetable oils, such as corn, safflower, and soybean oils (2). In this study of 1601 adults with and without asthma, it was found that plasma levels of one n-6 fatty acid, dihomo gamma linolenic acid (DHGLA), were associated with a diagnosis of asthma (3). DHGLA is a precursor for arachidonic acid, thus increased plasma levels may result in the generation of asthma-associated inflammatory mediators. However, it is not known if the increased plasma levels of DHGLA reflected dietary intake of vegetable oils or the decreased desaturase activity associated with asthma.

In summary, there is no evidence that fish oil supplements will help manage or prevent asthma attacks. In moderate doses (less than 3 grams/day), fish oil appears to be safe for most persons, including asthmatics. Because it can decrease platelet aggregation, fish oil should not be taken concomitantly with anticoagulant therapy or by persons with coagulopathies (2).

Barbara Swanson, DNSc, RN, ACRN

Associate Professor

Rush University College of Nursing

Chicago, Illinois

References

1.   Woods RK, Thien FC, Abramson MJ. Dietary marine fatty acids (fish oil) for asthma in adults and children. Cochrane Database Syst Rev 2004;4.

2.   Natural Medicines Comprehensive Database, online version.

3.  Woods RK, Raven JM, Walters EH, Abramson MJ, Thien FC. Fatty acid levels and risk of asthma in young adults. Thorax 2004;59:105-110.