Abstract: The searches identified 15 studies; four studies with 91 participants (children and adults) were included; duration of studies ranged from six weeks to six months. Two studies were judged to be at low risk of bias based on adequate randomisation but this was unclear in the other two studies. Three of the studies adequately blinded patients, however, the risk of bias was unclear in all studies with regards to allocation concealment and selective reporting. Two studies compared omega-3 fatty acids to olive oil for six weeks. One study compared a liquid dietary supplement containing omega-3 fatty acids to one without for six months. One study compared omega-3 fatty acids and omega-6 fatty acids to a control (capsules with customised fatty acid blends) for three months. Only one short-term study (19 participants) comparing omega-3 to placebo reported a significant improvement in lung function and Shwachman score and a reduction in sputum volume in the omega-3 group. Another study (43 participants) demonstrated a significant increase in serum phospholipid essential fatty acid content and a significant drop in the n-6/n-3 fatty acid ratio following omega-3 fatty acid supplementation compared to control. The longer-term study (17 participants) demonstrated a significant increase in essential fatty acid content in neutrophil membranes and a significant decrease in the leukotriene B4 to leukotriene B5 ratio in participants taking omega-3 supplements compared to placebo. This review found that regular omega-3 supplements may provide some benefits for people with cystic fibrosis with relatively few adverse effects, although evidence is insufficient to draw firm conclusions or recommend routine use of these supplements in people with cystic fibrosis. This review has highlighted the lack of data for many outcomes meaningful to people with or making treatment decisions about cystic fibrosis. A large, long-term, multicentre, randomised controlled study is needed to determine any significant therapeutic effect and to assess the influence of disease severity, dosage and duration of treatment. Future researchers should note the need for additional pancreatic enzymes.

Plain-language summary: This review includes four small studies which compare omega-3 supplements to placebo. In total there were 91 participants, including both children and adults. The studies lasted between six weeks and six months. One six-week study reported that lung function and clinical status improved when taking omega-3 supplements. Volunteers also produced less sputum when taking omega-3 supplements. Two longer studies found that people taking omega-3 supplements showed definite increases in levels of essential fatty acids in their white blood cell membranes and also in levels of phospholipids (molecules that provide structure and protection to cells) measured in blood samples. Few side effects were reported in any of the studies. We conclude that regular omega-3 supplements may benefit people with cystic fibrosis with few side effects. However, there is not enough evidence from the four small studies included in this review to draw firm conclusions or recommend the routine use of these supplements in people with cystic fibrosis. Larger and longer trials are needed to assess the clinical benefit of omega-3 supplementation and to determine the appropriate dosage. We do not think there are any factors in the way the studies were run which will influence the results in a negative way. It was not clear if these studies had any other risk of bias which might affect the results.