Only two out of ten fish oil supplements sold in pharmacies contain sufficient omega-3 fatty acid to have any effect on joint pain, a New Zealand study has found.

For many fish oil products, people with arthritis would have to take three times the recommended number of capsules to get the required dose of omega-3 polyunsaturated fatty acids (PUFAs) for relief of tender joints.

The top ten over-the-counter fish oil supplements were analysed by scientists at the University of Canterbury in Christchurch to see if their recommended doses would provide the intake of 2.7 g/day of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) required to achieve anti-inflammatory effects in patients with arthritis.

Even if they contained all the omega-3 fatty acids claimed on the label and the number of capsules were taken as advised, only two of the ten products would meet the recommended intake of 2.7g/day for joint pain,  according to a study published in the NZ Medical Journal.

Based on the label claims, most of the fish oil products would provide between 800-1800mg of EPA and DHA daily, only two contained 2700mg or more of the omega 3 fatty acids.

In findings disputed by manufacturers, the researchers said only 40% of the products were found to contain amounts of EPA and DHA stated on the label when analysed by an independent laboratory using gas chromatography.

The researchers said  previous studies had found the levels of omega 3 fatty acids in fish oil products were lower than claimed on the label, probably due to oxidation and degradation after manufacture.

Manufacturers of fish oils claimed the study was flawed because the researchers did not calculate the actual omega 3 levels based on a per g of capsule basis.