Fish oil supplements, once touted as the natural substance that could alleviate many of your chronic ailments, may not prove to be helpful to obese/overweight adolescents and young adults with uncontrolled asthma, new research suggests.

The study, published in the American Journal of Respiratory and Critical Care Medicine, showed 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 lead author Jason E. Lang, Associate Professor at the Duke University in the US. 

"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," Lang added. 

The team included nearly 100 overweight or obese participants aged 12 to 25 and found that the participants had poor asthma control despite using a daily inhaled corticosteroid to control their asthma. 

For every three participants assigned to take fish oil for 25 weeks, one was assigned to take the soy oil placebo.

In addition, the team also looked at whether a variant in the gene ALOX5 affected the 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 researchers noted that the study's negative findings may not be the last word on fish oil and asthma and acknowledged that larger doses of fish oil over a longer period of time may produce a different result.

However, based on the current study, "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", said Lang.

New therapeutic interventions to reduce airway inflammation and facilitate improved asthma control are greatly needed, the team suggested.