Fish oils are amongst the most popular dietary supplements used throughout the developed world. They contain large quantities of omega-3 long-chain polyunsaturated fatty acids (n-3 PUFA), in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have widely reputed health benefits including reduction of inflammation and cardiovascular disease risk and improved mental performance. However these compounds are unstable under some conditions and are readily oxidised to other chemicals, the effects of which are unknown.
Prior to investigating specific physiologic effects of fish oil supplementation, Liggins Institute researchers carried out detailed analysis of EPA and DHA content and degree of oxidation of fish oil capsules marketed in New Zealand. Their results showed that only three of the 32 products tested contained the concentrations listed on the label while over half exceeded the recommended levels of oxidation products. In addition, they found these measurements were unrelated to “best-before” date, price or country of origin.
Researchers used validated chemical methods to analyse concentrations of EPA, DHA and recognised oxidation markers for all fish oil capsules available in New Zealand through retail and online stores at that time. Analyses and results were standardised to allow valid comparisons across all products.
Details of the study have been published in the journal Scientific Reports: Albert, B.B. et al. “Fish oil supplements in New Zealand are highly oxidised and do not meet label content of n-3 PUFA”. Sci. Rep. 5, 7928; DOI:10.1038/srep07928 (2015).
The authors observed that the very similar composition data listed on product labels could reflect reliance on data from companies that extract and supply raw fish oil product to individual brands and do not take into account effects of transport, encapsulation, packing, storage and seasonal variation.
Research leader, Liggins Institute Director Professor Wayne Cutfield says that further work is needed to discover how the varying degrees of decomposition affect the reputed health benefits of over-the-counter fish oil capsules.
“Future studies should investigate how different storage conditions affect the oxidation process. Importantly, they should take into account the effects of typical retail and home storage conditions on the rate of n-3 PUFA oxidation.
“In addition, any reports of the physiologic or metabolic effects of fish oil capsules should include measured levels of the main oxidation products so we can better understand how oxidation impacts upon the effectiveness of the supplements and whether there are any harmful side effects,” he says.
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