How does high DHA fish oil affect health? A systematic review of evidence

ABSTRACT

The health benefits of fish oil, and its omega-3 long chain polyunsaturated fatty acid content, have attracted much scientific attention in the last four decades. Fish oils that contain higher amounts of eicosapentaenoic acid (EPA; 20:5n-3) than docosahexaenoic acid (DHA; 22:6n-3), in a distinctive ratio of 18/12, are typically the most abundantly available and are commonly studied. Although the two fatty acids have traditionally been considered together, as though they were one entity, different physiological effects of EPA and DHA have recently been reported. New oils containing a higher quantity of DHA compared with EPA, such as fractionated and concentrated fish oil, tuna oil, calamari oil and microalgae oil, are increasingly becoming available on the market, and other oils, including those extracted from genetically modified oilseed crops, soon to come. This systematic review focuses on the effects of high DHA fish oils on various human health conditions, such as the heart and cardiovascular system, the brain and visual function, inflammation and immune function and growth/Body Mass Index. Although inconclusive results were reported in several instances, and inconsistent outcomes observed in others, current data provides substantiated evidence in support of DHA being a beneficial bioactive compound for heart, cardiovascular and brain function, with different, and at times complementary, effects compared with EPA. DHA has also been reported to be effective in slowing the rate of cognitive decline, while its possible effects on depression disorders are still unclear. Interestingly, gender- and age- specific divergent roles for DHA have also been reported. This review provides a comprehensive collection of evidence and a critical summary of the documented physiological effects of high DHA fish oils for human health.

KEYWORDS:

• 22:6n-3
• Docosahexaenoic acid
• Tuna oil
• Omega-3
• Seafood
• Health benefits

Conflict of interest

The Authors, SGF and GE are employees of Nu-Mega Ingredients Pty Ltd, a manufacturer and supplier of high DHA fish oil products. Nu-Mega Ingredients Pty Ltd. provided support in the form of salaries for authors SGF and GE, but did not have any additional role in the study design, data collection, analysis and interpretation, decision to publish, or preparation of the manuscript.

The authors' responsibilities

SGF, AJS and GE conceived the study. SGF, AJS and GMT developed the selection criteria. SGF and FW performed the literature search and review. SGF, FW, AJS, GE and GMT wrote the paper.

Acknowledgements

This research did not receive any specific grant or other direct monetary support from funding agencies in the public, commercial, or not-for-profit sectors. The authors wish to thank Yi Wan, Mek Cheng and Bo Wang for their assistance in the literature search and technical assistance in drafting the tables, and Bianca Szkuta for the careful revision of the final draft.