A sweeping and inclusive look at facts, fiction and questions surrounding omega 3 fatty acids and their relation to human health. Includes contributions from FAB's Dr Alex Richardson and Professor Michael Crawford.
For years, fish oil capsules have been touted as a shortcut to a healthy heart, brain and joints.
Based on the premise that populations who consume large amounts of fish are healthier, with lower rates of clogged arteries, heart disease, dementia and rheumatoid arthritis — probably because of the high levels of omega-3 fatty acids these foods contain — supplements seemed to be a pragmatic way of getting more omega 3 into our diets.
Many Brits dislike the taste of oily fish, and certain varieties such as salmon and fresh tuna are expensive. So why not simply extract the golden elixir they contain and pop it into a capsule?
Worth it? Supplements seemed to be a pragmatic way of getting more omega 3 into our diets, but a number of studies have rubbished the suggestion
Yet, in recent months, several large studies have poured cold water on the most long-established of these claims: that fish oil supplements protect the heart.
The latest, published by the Cochrane Collaboration — widely perceived as the gold standard for medical decision-making, because it pools together the results of the world’s most reliable trials — concluded that omega-3 supplements have little or no effect on our risk of heart disease, stroke, or early death.
Meanwhile, a separate analysis of ten omega-3 supplement trials published in the Journal of the American College of Cardiology in March reached a similar conclusion.
‘It reaffirms our current knowledge about omega-3 supplements and the advice that we give,’ says Tracy Parker, a dietitian for the British Heart Foundation.
‘Current evidence does not support the use of omega-3 supplements in the general population for the prevention of heart and circulatory diseases.’
It seems many of those taking fish oil for their hearts are somewhat behind the curve. And yet as the review also pointed out, omega-3s are essential for health.
WE STILL DON'T EAT ENOUGH FISH
Two omega 3s in particular: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — both found in oily fish, nuts and seeds, rapeseed oil and leafy green vegetables — have been shown to play an important role in brain function, as well as reducing inflammation in the body which is associated with many chronic diseases.
Some scientists fear this latest study will undermine efforts to increase omega 3 consumption in a nation of already reluctant fish-eaters, with consequences for our health.
So, what’s the truth about fish oil? Have we been wasting our money, or, in paying too much attention to this latest research, do we risk throwing the salmon out with the seawater?
There is no specific recommended daily allowance of omega 3 in the UK, but the Scientific Advisory Committee on Nutrition suggests that we eat at least two portions of fish per week — one of which should be oily, such as salmon, mackerel or sardines.
For adults, a portion size is around 170g of uncooked fresh fish, or a small can of oily fish.
According to the guidelines: ‘This recommendation represents a minimal and achievable average population goal and does not correspond to the level of fish consumption required for maximum nutritional benefit.
Our obsession with fish oil has a long history: the Greek physician Hippocrates believed that dolphin liver oil could improve the skin, while the 18th-century doctor Thomas Percival claimed that cod liver oil could cure arthritis.
Then, in the Thirties, parents started spooning cod liver oil down their children’s necks after it was discovered to contain large amounts of vitamin D and could prevent rickets.
This interest was rekindled in the Seventies, when scientists visiting remote villages in Greenland noticed a paradox: despite an extremely high-fat diet of whale meat, seal blubber and fish, the rate of heart disease in the Inuit population was strikingly low.
WHY FATTY FISH HAS MORE OMEGA 3
They suggested that omega 3s, which are not only present at high levels in oily fish, but in the samples of Inuit blood they had collected, might be the reason. (The omega 3s in fatty fish derive from the fish’s diet of krill or algae, and are stored throughout their bodies — rather than concentrated in their livers, as with white fish such as cod).
However, we can also make omega-3s from alpha-linoleic acid (ALA), a substance found in nuts and seeds, particularly walnuts, and flax and chia seeds.
These fatty acids do several things. For example, they get into the membranes that separate the insides of cells from their external environment, changing how they respond to signals from elsewhere in the body.
‘We think that omega 3s in the cell membrane make cells behave in a more optimal way,’ says Professor Philip Calder, a nutritional immunologist at the University of Southampton.
We also use them to make other important substances. In 1982, the Nobel Prize for Medicine was awarded to three researchers who discovered the role that chemicals called eicosanoids play in our body. Produced from omega 3s — but also the omega 6 fatty acids found in meat, eggs and vegetable oil — these substances regulate many processes in our body, from immunity, to blood pressure, blood clotting and brain cell signaling.
‘The 1982 Nobel Prize put the seal on what is now a huge body of scientific evidence on the function and essentiality of these fatty acids,’ says Professor Michael Crawford, director of the Institute of Brain Chemistry and Human Nutrition in London.
THE LINK TO HEART DISEASE
Relevant to heart disease is the discovery that omega 3s are used to make substances that dampen inflammation. Omega 6s, on the other hand, make substances that promote it.
‘Heart disease is caused by the build-up of fatty material in blood vessel walls, and inflammation is part of that process, so it may be that the inflammation-resolving effects of omega 3s are important there — as well as other things they do such as lowering blood pressure and levels of fats called triglycerides,’ says Professor Calder.
The idea that omega 3s protect the heart was strengthened in 1989, with a study in The Lancet.
Gulp! We spend £420 million on supplements each year, about the same as we spend on gin
Involving 2,033 men who had already experienced a heart attack, it found those who upped their oily fish consumption were 29 per cent more likely still to be alive two years later. ‘A modest intake of fatty fish (two or three portions per week) may reduce mortality in men who have recovered from a heart attack,’ the authors concluded.
Other studies followed, and by 2002, the American Heart Association felt there was enough evidence to release a scientific statement that omega 3s reduce the incidence of cardiovascular disease, advising people to eat at least two servings of fish per week, as well as consuming foods rich in AHA, such as walnuts and flaxseeds. And those with existing cardiovascular diseases should consider taking omega-3 supplements, too, it said.
The British Heart Foundation followed suit, recommending everyone have two portions of fish per week (at least one of them oily); people who’d already had a heart attack should have two to four portions of oily fish, or take fish oil supplements, to reduce their chances of another.
However, the British Heart Foundation changed this advice in 2013, following guidance by the National Institute for Health and Care Excellence (NICE), which said people should stop taking fish oil supplements for the prevention of cardiovascular disease because they were ineffective.
By now, many of those at high risk of heart disease, or who had already suffered a heart attack, were taking cholesterol-lowering statins, or undergoing surgical procedures such as angioplasty (opening up the blocked vessels by inserting a tiny metal tube) or coronary bypass.
NICE felt that the impact of better medications and surgery techniques ‘was far more important in terms of reducing the risk of a second heart attack than taking expensive omega-3 supplements or trying to eat three to four portions of oily fish’, says Tracy Parker.
So it wasn’t necessarily that they weren’t effective, they just weren’t as effective as other options. For the general population the advice remains to have two portions of fish weekly, one of which should be oily.
QUESTIONS ABOUT THE RESEARCH
Consuming this amount of fish, should provide approximately 450mg/day of the omega-3 fatty acids DHA and EPA, however, typical UK intakes are below 150mg/day.
This month’s Cochrane Review was commissioned by the World Health Organisation which is in the process of updating its guidance. It involved combining the results of 79 previous studies — involving 112,059 participants in total — which is known as a meta-analysis.
‘One reason for putting all the trials together is to make sure we have enough people in enough trials for long enough so if there is an effect we can pick it up,’ explains Lee Hooper, a dietitian at the University of East Anglia, who led the study.
Good for you? Eating a Mediterranean diet, which is rich in oily fish, but also fruit and vegetables, nuts, beans and olive oil, is associated with a healthy heart
Its conclusions were a fishslap to the omega-3 supplements industry — if not the fishing industry.
For in contrast to other studies, the Cochrane review also concluded that the evidence for eating oily fish is weak. ‘While oily fish is a healthy food, it is unclear from the small number of trials whether eating more oily fish is protective of our hearts,’ says Lee Hooper.
Yet although they don’t necessarily dispute the findings about supplements, some researchers question the relevance such meta-analyses of nutrition research has — some of the studies Cochrane looked at included healthy men and women, others at those with existing cardiovascular disease.
There was also inconsistency in the type of omega-3 supplement they took, the amount of omega-3s these supplements contained, and how long they were taken for.
Lee Hooper says she took pains to split the analysis into different sub-groups to deal with some of this variability, but other researchers argue that the trials were too mixed to draw firm conclusions.
SUPPLEMENTS VS. OILY FISH
‘The problem with meta-analyses is that you can only work with the evidence you have, so if you put garbage in, you get garbage out,’ says Dr Alex Richardson, a senior research associate at the University of Oxford and director of Food and Behaviour Research.
‘The studies included in this latest meta-analysis are a hotchpotch, because quite frankly there just aren’t enough good-quality studies to answer this question of whether omega-3 supplements reduce the risk of heart disease.’
One reason could be that omega-3 trials tend to be sponsored by supplement companies, which often don’t have the money or motivation to do the kind of large, rigorous trials required of drug companies. ‘You can’t follow people around for years, measuring them and making sure they’re eating everything they’re supposed to,’ says Dr Richardson.
Myth? Unlike drugs, which work quickly, nutrients are thought to take effect over a longer time
Also, unlike drugs, which tend to work quickly, nutrients are thought to exert their effects over a longer timescale — often in synergy with other things in the diet. This may be one reason populations that eat large quantities of fish appear to be healthier.
For example, eating a Mediterranean diet, which is rich in oily fish, but also fruit and vegetables, nuts, beans and olive oil, is associated with a healthy heart.
‘However, if people really don’t like, and won’t touch, fish, I think that is a rational case for the use of supplements because otherwise you really are going to be way down there in terms of your tissue content of EPA and DHA,’ says Dr Richardson, who has previously received research funding from companies that produce omega-3 supplements.
Professor Calder points out that scientific trials of eating fruit and vegetables also haven’t proved that they reduce the risk of deaths from cardiovascular disease or cancer, but no-one disputes that they are healthy.
‘It’s exactly the same for fish,’ he says (Professor Calder has served on the scientific advisory boards of several companies that make supplements).
COULD THEY EASE DEPRESSION?
BY focusing too heavily on cardiovascular health, many fatty acid researchers worry that other benefits of omega 3 consumption are being overlooked, such as their importance to brain health.
‘I would be worried if people changed their behaviour on the basis of this review, because even if not everyone is gaining a health advantage from [eating fish], there would be some people who would lose their health advantage,’ says Professor Calder.
Some of the strongest evidence for the importance of omega 3s to brain health comes from studies of serious depression. Indeed, the American Psychiatric Association recommends people with clinical depression to take omega-3 supplements, after a 2006 meta-analysis of eight studies concluded there was a benefit to doing so.
Studies that look at populations (rather than comparing a group given fish oil compared with those not given it) ‘fairly consistently’ show that those who eat more fish tend to have less depression and less neurodegenerative conditions such as dementia,’ says Dr Simon Dyall, a neuroscientist at Bournemouth University who researches the role of fatty acids in the brain (he has has grants from Efamol Ltd which makes supplements).
He, too, would recommend eating more oily fish, rather than resorting to supplements, but believes they could have a role in brain health nonetheless.
‘The first line should always be “eat more oily fish”, but as a population we tend to be quite averse to doing so.
At the moment the evidence is weak, but it does suggest that taking supplements is better than not taking supplements,’ he says.
About 60 per cent of brain and nerve tissue is composed of fatty acids, including omega 3s.
They make the membranes that encase nerve cells and enable them to transmit electrical signals, and the myelin sheaths that wrap around them and speed up these transmissions; they also provide the raw ingredients for many substances brain cells use to communicate.
This can make it difficult to assess their true importance, says Dr Dyall.
‘When you’re looking at a drug, you can say “it targets this receptor or this particular pathway”, but when you’re looking at fatty acids they are such a fundamental molecule that it’s very complicated to delineate exactly what the pathway is that they are having a positive effect on.’
In the past decade, researchers have woken up to the idea that chronic low-grade inflammation is implicated in just about every chronic non-communicable (i.e. you don’t ‘catch’ it) disease going, from depression, to diabetes to obesity. It is also part of what goes wrong in autoimmune diseases such as rheumatoid arthritis, where the body’s immune cells start attacking the joints.
The impact of taking omega-3s has been reasonably well studied in people with rheumatoid arthritis, says Professor Calder, and the evidence that they can reduce pain in rheumatoid arthritis is quite good: ‘Those studies used very high doses of omega 3s — much higher than most people could take easily,’ he cautions. ‘But that isn’t to say that someone who takes a couple of fish oil capsules per day might not get some pain relief.’
Osteoarthritis — wear and tear of the joints — is also increasingly believed to have an inflammatory component, so it’s possible omega 3s may have a role to play there as well.
SO WHAT'S THE BOTTOM LINE?
Despite the uncertainty about the usefulness of omega-3 supplements, most experts agree on one thing: omega 3 consumption is crucial to human health.
Quite how much of them we need — and whether they can prevent serious diseases from occurring, or merely lessen their impact — remains unclear.
But if you struggle to eat fish, and are concerned about your omega 3 consumption, rather than expensive fish oil pills, there may be another thing you can do, cut down on omega 6.
Omega 3 and omega 6 fatty acids exist in equilibrium with each other in the body; if you consume too many omega 6s — as you would if you eat a lot of meat and/or heavily processed food containing large amounts of vegetable oil — this will tip the balance towards more inflammation, and they will also begin to dominate in cell membranes, reducing cells’ responsiveness to hormonal or electrical signals from elsewhere in the body.
Indeed, this may be another reason fish-eaters appear to be healthier: they simply eat less meat and enjoy a more varied diet overall. The bottom line is that we evolved to eat a diet containing many different types of food.
So we should only be reaching for food supplements as a very last resort.