To the Editor: We were distressed to read yet another randomized controlled trial comparing fish oil with olive oil supplements being interpreted as evidence that such supplements are ineffective.1 It may well be that fish oil is not more effective than olive oil but does that mean that neither is effective?
There is ample evidence that olive oil supplements have effects on the cardiovascular system.2 One of the first large neutral trials of cardiovascular prevention, the World Health Organization clofibrate trial, used olive oil capsules as a placebo.3 Could this choice of placebo have influenced the result? A recent meta-analysis4 of randomized trials of fish oils suggested no overall benefit, but many of the trials used olive oil as the placebo. The analysts excluded Grupo Italiano per lo Studio della Sopravvivenza nell’Infarto Miocardio (GISSI)-Prevenzione because it was not a blinded study, even though the study showed a reduction in mortality. The meta-analysis also reported the placebo in the GISSI-Heart Failure5 study as nonoil although it was olive oil (Luigi Tavazzi, MD, written communication, December 14, 2012).
Cleland JGF, Joseph A, Pellicori P. Fish Oil vs Olive Oil for Postoperative Atrial Fibrillation. JAMA. 2013;309(9):871–872. doi:10.1001/jama.2013.670
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