I am so annoyed by omega-3s, the fatty acids contained in fish products and some vegetable oils, that I try and steer clear of foods they have been added to. This is quite difficult: everywhere there is assertive marketing of their benefits in products such as pasta, milk, margarine, yoghurt and eggs. Advocates claim they can alleviate or prevent everything from heart disease to children’s behavioural problems to depression.

Traditionally, fish oils have had a medicinal status in British households. Generations of children have been fed spoonfuls of the stuff as a general preventative measure and “brain food”. The problem lies not with the oils but with science, which has taken too long to test these claims properly.

It would be wonderful if there were a key to unlocking these types of problems. But I really don’t like the claims that omega-3s are more beneficial when taken in bigger quantities than you would naturally get in food; and that they possess the power to treat or cure a variety of things when the evidence is more tentative.

It’s not hard to see why they have become so popular – fish oils seem “natural” and thus less harmful than drugs. But the marketing of them seems unfair, tugging at emotions of people more worried about their wellbeing than scientific proof.

I’m especially interested in the claimed effects of omega-3 on depression. Depression makes people see the world and their place in it differently. It can be difficult to have the perspective on an illness that one normally would. Also, relatives or friends are often prepared to do anything that has
“a chance” of working.

In this context, doctors must be careful what treatments they recommend. Some private clinics are keen to use omega-3s for depressive symptoms where the recommended supplements cost between £10 and £20 a month.

So what is the proof? There is some evidence that omega-3 oils are useful after a heart attack but the effect remains rather unclear. Similarly, for the prevention of dementia, a Cochrane review (where all the evidence is synthesised) says: “There is a growing body of evidence…that suggests a protective effect of omega-3…against dementia. However, until data from randomised trials become available for analysis, there is no good evidence to support the use of dietary or supplemental omega-3.”

Last month, the independent Drugs and Therapeutics Bulletin asked whether omega-3s should be recommended as a supplement or initial trial in the treatment of depression. The review notes that in epidemiological studies, where patterns are observed between a population and their diet, higher amounts of fish consumption seem to be inversely related to depression (though an association does not prove cause and effect). There is also some evidence that a lower dietary intake of omega-3 fats is associated with more severe depression.

However, the DTB concludes that “despite the observational evidence with reduced intake of long-chain omega-3 fatty acids, there is no convincing basis for using these nutrients as a sole treatment for the condition. There is limited evidence suggesting that long-chain omega-3 fatty acid supplements might help to relieve depression when given in addition to existing antidepressant medication. However, this needs confirming before we can recommend the routine use of such supplements [for] depression.”

The DTB recommends caution and the gathering of further data, which is definitely a good thing. The problem is that we are desperate for a “cure”, a “magic bullet”. Fish oils may not seem to be at first glance as undesirable as other generations’ purported cure-alls, such as diazepam (or Valium, “mother’s little helpers”), which thousands of people became addicted to. Surely the very idea that control of normal moods should always lie with a tablet is a dangerous precedent to follow.

So what does help? Antidepressants such as fluoxetine may help some people but come with side effects, take weeks to start working and the evidencefor their benefits is patchy. Exercise helps but when it is a struggle to face the world, it can be difficult to push oneself to manage the regular and vigorous exertion that has been shown to improve mood. Sometalking therapies are proven to help, though waiting lists are usually long – several months in my area, for instance. The computer programs that deliver some cognitive therapies may be useful for some but many people need human warmth when unburdening themselves and the insight that others can bring.

So omega-3s might well have a role in treating depression. Then again, they might not. If we are going to learn anything from past supposed miracle cures, it is that we have to get the evidence in first, not after we have assumed that something works. It would make far more sense to put everyone using omega-3s for depression into a clinical trial where we could examine their effects in a fair way. It’s time to sort out the helpful from the hype.

Margaret McCartney is a GP in Glasgow
More columns and further reading at www.ft.com/mccartney

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