Fish oil does not improve asthma control

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Fish oil does not appear to improve asthma control in adolescents and young adults with uncontrolled asthma who are overweight or obese, according to research. Dr Jason E Lang and co-authors report that four grams of fish oil a day for six months did not improve asthma control, as measured by a standard asthma control questionnaire, breathing tests, urgent care visits and severe asthma exacerbations.

“We don’t know why asthma control in obese patients is more difficult, but there is growing evidence that obesity causes systemic inflammation,” said Lang, lead study author and associate professor of paediatrics at Duke University. “Because the omega-3 fatty acids in fish oil have anti-inflammatory properties, we wanted to test whether fish oil would have therapeutic benefits for these patients.”

The 98 overweight/obese participants in the study ranged in age from 12 to 25 (average age: 14.6). All were diagnosed with asthma by a physician but had poor asthma control, despite using a daily inhaled corticosteroid to control their asthma. About half the participants were African American. For every three participants assigned to take fish oil for 25 weeks, one was assigned to take the soy oil placebo.

The researchers also looked at whether a variant in the gene ALOX5 affected study findings. It is known that mutations in the gene can reduce responses to anti-leukotriene drugs. Leukotrienes are inflammatory molecules that play a critical role in triggering asthma attacks. In this study, the ALOX5 variant did appear to be linked to leukotriene production but not to the effectiveness of fish oil in providing asthma control.

The authors wrote that the study’s negative findings may not be the last word on fish oil and asthma. They acknowledged that larger doses of fish oil over a longer period of time may produce a different result.

Based on the current study, however, “there is insufficient evidence for clinicians to suggest to patients with uncontrolled asthma that they should take daily fish oil supplements to help their asthma,” Lang said.

Rationale. Omega-3 fatty acid (n3PUFA) supplementation has been proposed as a promising anti-asthma strategy. The rs59439148 ALOX5 polymorphism affects leukotriene production and possibly inflammatory responses to n3PUFA. Objective. Assess the effects of n3PUFA supplementation and ALOX5 genotype on asthma control in patients with obesity and uncontrolled asthma. Methods. This multi-center trial among 12-25 year olds with overweight/obesity and uncontrolled asthma randomized subjects in a 3:1 allotment to n3PUFA (4g/day) or soy oil control for 24 weeks. Asthma Control Questionnaire (ACQ) was the primary outcome; secondary outcomes included blood leukocyte n3PUFA levels, urinary leukotriene-E4 (uLTE4), spirometry, and asthma-related events. The number of SP1 tandem repeats in rs59439148 determined ALOX5 genotype status. Simple and multivariable generalized linear models assessed effects on outcomes. Results. Ninety-eight participants were randomized (77 to PUFA, 21 to control), and > 86% completed all visits. Asthma and demographic characteristics were similar among treatment groups. N3PUFA treatment increased n3-to-n6PUFA ratio in granulocytes (p=0.003) and monocytes (p=0.002), but did not affect mean (95% CI) ACQ change at 6 months (N3PUFA: -0.09 (-.09, .10) vs. control: -0.18 (-.42, .06), p=0.58). Changes in uLTE (p=0.24), FEV1 percent predicted (p=0.88) and exacerbations (RR=0.92, 95% CI 0.30-2.89) at 6 months were similar in both groups. N3PUFA-treatment was associated with reduced asthma-related phone contacts (RR=0.34, 95% CI 0.13-0.86, p=0.02). ALOX5 genotype did not affect n3PUFA treatment responses. Conclusion. We did not find evidence that n3PUFA use improves most asthma-related outcomes and cannot recommend it as a prevention strategy for overweight/obese patients with asthma.

Jason E Lang, Edward B Mougey, Md Jobayer Hossain, Floyd Livingston, P Babu Balagopal, Scott Langdon, John J Lima

American Thoracic Society material
Annals of the American Thoracic Society abstract

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