Fish oil supplements not a fix for obese patients with asthma

March 1, 2019

Although fish oil supplements did not improve asthma exacerbations in children who are obese or overweight, the question remains whether fish oil could help other types of children with asthma.

Whereas fish oil may have a host of benefits as a dietary supplement in the general population, a new study reveals that supplementation did little to improve outcomes for overweight or obese children with uncontrolled asthma.

The study, published in the Annals of the American Thoracic Society, found no improvement in severe asthma exacerbations or emergency care visits in children who were given 4 grams of fish oil daily for 6 months compared with those who were given a placebo.1 Improvement was measured based on self-reported outcomes and breathing tests, according to the report.

Jason E. Lang, MD, MPH, associate professor of Allergy, Immunology, and Pulmonary Medicine at the Duke University School of Medicine, Durham, North Carolina, director of the Duke Clinical Research Institute, and lead author of the study, says at this point the study was not able to justify a recommendation for clinicians to use omega-3 fatty acid supplements for the purpose of improving asthma.

“The evidence at this point for omega-3 fatty acids improving asthma is scant and mainly theoretical. It is possible that future research will find that certain subgroups of patients with asthma will respond, but that is speculation,” Lang says. “Our study demonstrated that among patients who took fish oil and had increases in their blood omega-3 fatty acid levels, asthma did not improve. Furthermore, a proposed mechanism has been that omega-3 fatty acids will help patients by reducing arachidonic acid pathway inflammation, specifically leukotrienes. Unfortunately, we did not see any reductions in leukotrienes in patients taking the supplements.”

Some studies have linked the omega-3 fatty acids found in fish oil to lower incidence of asthma, and the study team sought to test the theory in overweight and obese children-a population particularly at risk for poor asthma control. Lang’s trial was the largest to evaluate the effect of fish oil supplementation in asthma patients, with 98 patients aged 12 to 25 years enrolled in the study. Participants who were given fish oil supplements throughout the study showed elevated levels of omega-3 in their blood, but there were no improvements in asthma control and lung function measures or on the participants’ Asthma Control Questionnaire (ACQ) at 3 or 6 months into the study, according to the report. The only improvement noted over the study period was a decrease in the number of calls participants made to their physicians related to asthma symptoms. John La Puma, MD, FACP, founder of Chef Clinic and co-founder of ChefMD, Santa Barbara, California, has discussed the benefits of fish oil supplements for patients with asthma on his professional blog, and says he thinks the participants in Lang’s study may have had benefits obscured by other physiologic conditions, including obesity. He isn’t ready to discount the benefits of supplementation just yet, despite Lang’s findings.

“The finding that they made fewer calls to their physician may well be simply because they were asked to take a medication and the psychological effect of so doing helped them,” La Puma says, “but their lung function was no better and, although obesity is likely a cause of chronic inflammation, there are many better ways to get the benefits of both omega-3s-such as eating fish-and reducing inflammation by eating foods that are very high in anti-inflammatory agents.”

Augusto A. Litonjua, MD, MPH, division chief of Pediatric Pulmonary Medicine at the University of Rochester School of Medicine and Dentistry, Rochester, New York, has been involved in prior studies of fish oil supplementation in patients with asthma and notes that prior research has shown inconsistent results in this area.

“This study is different in that the investigators focused on obese asthmatics. We do not know if metabolism of omega-3 fatty acids are different in obese versus nonobese asthmatics,” Litonjua says. “Additionally, reviewing Figure 3 [in Lang’s study], it is clear that only a proportion of the participants in the treatment arm responded with an increase in their n-3 PUFA level. We do not know if the participants who had the significant increase in their n-3 PUFA levels responded differently from those whose levels did not increase. A larger study would need to answer this question.”

Litonjua says it has been suggested that genetic differences may help explain why some patients respond to omega-3 supplementation while others do not.

“The investigators (in Lang’s study) attempted to show whether genetic differences in the ALOX5 gene promoter modified the response to fish oil supplementation and they did not find any differences,” Litonjua says. “However, for this genetic modification study, a larger sample size may be needed, and additional genes from the metabolic pathways may need to be examined.”

Litonjua notes that fish oil supplementation is not part of the standard of care for asthmatics-something that is not likely to change.

“I think the results of this study support the notion that supplementation does not help at the dose (4 g/day) that was used for this study in obese asthmatics,” Litonjua says. Lang says that because the study was conducted on sedentary, obese patients, future research may produce different results on patients with exercise-induced symptoms. The research team will also continue to analyze its findings, specifically pertaining to other types of inflammation, he says.

Moving forward, Lang says he hopes clinicians and patients will approach these supplements with caution. “I hope that patients with asthma will think twice before taking supplements for the purpose of improving asthma,” Lang says. “In certain cases, supplementing the diet can be beneficial but all treatments can have adverse effects and monetary costs.”

The study findings aren’t the end-all, however, says Lisa Wood, PhD, a professor in the School of Biomedical Science and Pharmacy at the University of Newcastle in Australia. Wood says recent systematic literature reviews have shown benefits of fish oil supplementation early in life (at age 6 to 9 months) and regularly throughout childhood to reduce asthma and wheezing in young children, but also acknowledges that all these studies were observational.

“The study by Lang and colleagues is a high-quality, carefully conducted intervention in the subgroup of children with asthma who are obese. Obesity, which creates a proinflammatory environment, is a potential confounder that has not been previously considered in the context of asthma/fish oil supplementation,” Wood says. “This study suggests that the presence of obesity or associated factors such as background physical activity levels and dietary intake may negate the potential benefits of fish oil.”

Although the Lang study determined supplementation yielded no benefit to asthma control in this population, supplementation with omega-3 should not necessarily be discounted altogether.

“There remains a lack of evidence supporting the use of fish oil supplementation in obese asthmatic children. However, as with the general population, it is recommended that fish be consumed as a regular component of a healthy diet,” Wood notes.

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