By Otto Baynes

In spite of decades of study, medical science is still unclear about many of the frequently touted health benefits of fish oil. Recommendations for the use of fish oil as a supplement often stem more from anecdotal cultural evidence than they do from definitive scientific evidence.

Fish oil is promoted for cardiovascular well-being, osteoporosis, menstrual cramps, certain psychological disorders, and for treatment of the symptoms of rheumatoid arthritis. Before tackling each of these sets of claims, however, it’s important to have a basic understanding of how fish oil acts to protect the body.

How Fish Oil Works

There isn’t anything inherent to the tissues of oily fish that promotes good health. It’s that these fish consume lots of microalgae, which are a source of two particular omega-3 fatty acids – EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Fish like salmon, tuna and sardines thus become the world’s richest concentrations of these two beneficial fatty acids by way of their diet.

Aside from filling a basic nutritional need, EPA and DHA reduce inflammation throughout the body. Unfortunately, that’s about the only thing science is absolutely certain of. While they seem to slow the progress and ease the symptoms of certain diseases, the exact mechanism by which they do so is not yet known.

Cardiovascular Health

Fish oil is most commonly advertised as being beneficial to “heart health”, but scientific studies have actually been very mixed on this point. A 2004 review of studies from the previous two years (1) found that those taking fish-based omega-3 supplements over a period of at least six months didn’t have any reduction in risk of cardiac events or mortality. A 2012 review of 14 previous major studies (2) also found insufficient evidence for omega-3 supplementation reducing cardiac events in patients with a history of cardiac disease. These results don’t discount a number of individual studies in which long-term EPA and DHA supplementation seemed to provide clear benefit, but they demonstrate that it’s impossible to conclusively say that fish oil helps to prevent cardiac events.

Evidence that fish oil reduces triglycerides (harmful fats) in the blood is more promising, though also still not conclusive. A comprehensive 2009 review of 47 studies of this nature that specifically used fish oil supplements with hyperlipidemic subjects found that there was a significant reduction of triglycerides (3). However, in some of these studies, LDL (“bad”) cholesterol was also raised.

Much of the belief in fish oil’s heart health benefit comes not from medical studies, but from cultures that traditionally eat a lot of fatty fish and have unusually low rates of cardiac disease. Examples are the Eskimos of Greenland (4), Inuit of Canada (5) and the traditional Japanese diet (6). While these cultures provide strong anecdotal evidence, it has yet to be validated by scientific testing.

Arthritis

Fish oil has been used to treat rheumatoid arthritis since the 1700s, and modern medical science tends to support its usefulness in treating symptoms (7). The benefit is restricted to temporarily easing pain and stiffness, however; it doesn’t slow the progress of the disorder.

Other Uses

The body of evidence supporting other uses for fish oil is much smaller.

At least one study of elderly women indicates fish oil supplementation improves calcium intake and bone density (8).

Two studies have shown relief of menstrual cramp pain in women, but one was paired with vitamin B12 supplementation (9,10).

A review of studies of the effect of omega-3 supplementation on psychiatric disorders indicated it may be very effective in managing symptoms of schizophrenia and depression (11). A meta-analysis of studies published up to 2013 also concluded that omega-3 supplementation was helpful in patients diagnosed with major depressive disorder (12). However, both studies caution that these results are preliminary and that further study is needed.

So What Is It Good For?

Fish oil’s history in easing arthritis symptoms is long and proven. The evidence for cardiovascular health is a little more reliant on incomplete medical study and cultural anecdote, but it’s still pretty strong. It shows at least some promise for all the other conditions listed, but further study is needed before it can be said with confidence that it will definitely help.

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