Fish oil's reputation for protecting our hearts and minds has taken some hits lately. Despite earlier promises of a benefit for ageing brains, one study reported last year that omega-3 supplements didn't appear to improve cognitive function in older people, while another review looking at prevention of heart disease and stroke concluded fish oil was not much help there, either.
In other areas, such as mental health, the oil's benefits should not be written off.
''Even though research into fish oil's effects on depression has had mixed results, it's an evolving story,'' says Gordon Parker, scientia professor at the school of psychiatry at the University of NSW. He believes the reason for conflicting findings may be that different formulations of fish oil supplements have different effects.
''We still need to work out which formulation is best for depression and at what dose,'' he says.
Fish oil contains omega-3 fats with names commonly known by their initials. There's EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both of which help regulate the brain chemicals that affect mood, and cool the inflammation thought to contribute to depression, arthritis, heart disease and dementia. To get enough of these fats we need fish. Two to three serves of oily fish, such as sardines, salmon, trout or mackerel, weekly delivers the daily 500 milligrams of omega-3 fat recommended by the Heart Foundation. Although we can make some of these fats ourselves by eating plant foods such as flaxseed, chia seeds and walnuts, which contain another omega-3 fat (ALA), we produce only a small amount.
For helping with depression, fish oil supplements containing more EPA than DHA appear to be the most effective, but more studies are needed, says Parker, former director of the Black Dog Institute, which specialises in treating and researching mood disorders. Although finding the optimal dose for depression is a work in progress, the institute generally recommends two 500 milligram capsules daily.
''Fish oil may also help protect young people from serious mental illness. An Australian study of adolescents at risk of schizophrenia found those taking fish oil supplements had a much lower risk of developing psychosis,'' he says. ''Although the general advice is two to three serves of oily fish each week, for adolescents and young people with an increased risk of psychosis or mood disorder, there's an argument for taking three or four capsules daily of a fish oil supplement containing 180 milligrams of EPA and 120 milligrams of DHA.''
Parker is working on a study* to see if fish oil helps women with bipolar disorder keep their moods stable during pregnancy. Pregnant women with bipolar are between a rock and a hard place - using mood-stabilising drugs is linked to an increased risk of pregnancy complications, but avoiding medication can seriously affect their mental health.
''We know that omega-3 supplements are safe in pregnancy and that they can help with depression in bipolar disorder when they're used in conjunction with medication. Now, we want to find out if omega-3 supplements alone can keep moods stable in pregnancy,'' Parker says.
Differences in the quality of fish oil supplements and the use of different doses can also explain mixed results in studies on cardiovascular disease, according to the Heart Foundation's director of cardiovascular health, Rob Grenfell. ''There's a lot more to learn about fish oil, but research so far suggests it helps keep blood vessels healthy and reduces the risk of clots by helping thin the blood,'' he says.