Here’s why I’ll keep taking fish oil pills despite the dementia study

Last week I read a headline that nearly made me choke on my fish-oil pill.

For years I’ve been taking a daily omega-3 supplement because I don’t eat enough oily fish.

This matters – partly because of the possible heart and anti-inflammatory benefits, but for me, mainly because the disease I fear most is dementia and my hope is that omega 3 will help prevent it.

So when I saw the headline about a new study suggesting omega-3 supplements might not protect against dementia but could actually be linked with faster decline, I panicked – not just worried about myself, but what I advise others, too.

The research, just published in The Journal of Prevention of Alzheimer’s Disease, was based on data from the Alzheimer’s Disease Neuroimaging Initiative, a major US dementia study where older adults are being monitored over years with memory checks, brain scans and various blood tests.

The researchers compared 273 people who take omega-3 supplements daily, with 546 similar non-users – and found that those taking fish-oil pills appeared to decline faster on several cognitive scores.

Interestingly, the researchers did not find that this was explained by more amyloid or tau plaques, or brain shrinkage – the classic changes we associate with Alzheimer’s.

Rather, they suggested the link may have been as a result of the brain’s poorer ability to use glucose due to oxidative stress. Oxidative stress is, put simply, a form of chemical wear and tear inside the body.

Researchers compared 273 people who take omega-3 supplements daily, with 546 similar non-users – and found that those taking fish-oil pills appeared to decline faster on several cognitive scores (picture posed by model)

This was the researchers’ theory – and it makes sense biologically, as we know that fish oils are delicate fats and if they are old, poor quality, or badly stored, they can become oxidised. And they could, in theory, add to the very oxidative stress we are trying to reduce.

So am I worried? The study was observational – where researchers look at what people are already doing, and then search for associations; for example, between using omega 3 and cognitive decline.

This sort of study can be useful because it suggests avenues for further research, but – crucially – it cannot easily prove cause and effect.

The problem is that people who forget names, misplace keys, struggle to find words or have a family history of dementia are understandably more likely to worry about their memory, and may be at higher risk anyway, and want to do something about it. They therefore buy fish oil pills because they’ve read how good they are for preventing dementia.

The curse of observational nutrition research is that it can make almost anything look good or bad depending on how the research is conducted.

Coffee once looked harmful in observational studies, because coffee drinkers were more likely to smoke.

Which is why, with a frightening headline, I want to know what the randomised controlled trials show.

These are studies where people are randomly assigned to receive either the treatment being tested or a placebo.

And when it comes to omega 3s and cognitive function, in a major review published recently in Scientific Reports, analysis of 58 randomised controlled trials from multiple countries suggested that omega-3 supplements may be associated with slightly better cognitive outcomes – or slower decline in some areas, particularly memory.

Although this is a much higher standard of evidence than an observational study, it is by no means perfect.

Not least as it pulled together lots of different studies involving different doses – and very different patients, from healthy adults to people who already had memory problems or dementia.

And many of the studies were short – the real benefit, or harm, of fish oils may only become clear after taking them for years.

The fairest reading of all this is that fish oils are neither magic nor poison, but that they may be somewhat beneficial.

In my view, if people are going to take omega 3s, choose a high-quality supplement (i.e. a known brand and within its use-by date) containing roughly 1,000mg a day of the omega-3 fats EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) – these are the main omega-3 fats found in oily fish and are thought to have most of the potential health benefits.

And remember, omega 3s were never only about dementia anyway.

Professor Rob Galloway has been taking a daily omega-3 supplement for years because he doesn’t eat enough oily fish. The disease he fears most is dementia and his hope is that omega 3 will help prevent it

The strongest evidence for the supplements is in reducing triglycerides, a type of blood fat linked with cardiovascular risk (indeed, people with very high triglyceride levels are often prescribed high doses of omega 3).

There is also evidence of anti-inflammatory effects, which is why some people with arthritis report less stiffness and joint pain taking them.

They may modestly help symptoms in some people with depression, too.

None of this means everyone has to take them. Nor does it mean they undo a bad lifestyle.

And if large, well-conducted randomised trials eventually show omega-3 supplements genuinely accelerate dementia or cause significant harm, I will stop taking them myself.

That is what medicine should be: not blind loyalty to a specific belief or supplement – and not panic about headlines – but following the evidence as it evolves.

@drrobgalloway