A study from New Zealand's University of Canterbury study that found there was often less omega-3s in most fish oil has been retracted. The authors now admit that they miscalculated their results.

​The study: Are over-the-counter fish oil supplements safe, effective and accurate with labelling? analysed 10 New Zealand fish oil supplements attempting to assess the accuracy of labels.

The researchers initially claimed that over half the supplements were not correct their labels as far a concentration is concerned. They thus said that fish oil supplements were unlikely to provide the claimed health benefits.

The authors, Julia Rucklidge, Shelby Hantz and Ian Shaw were about to have the paper published in the New Zealand Medical Journal. But have retracted the paper admitting that they had made errors. Errors were thus made in calculating the amounts of EPA and DHA in five of the fish oil supplements. The authors, therefore, underestimated the doses.

Julia Rucklidge said the authors apologised for the error.

"As soon as we realised our error, we contacted the editor of the New Zealand Medical Journal to request that our paper be retracted," she said.