As a young child I recall my grandmother giving me the largest spoonfuls of cod liver oil, coaxing me with the promise of an equally large spoonful of golden syrup. It was probably a throwback to her own childhood when the post-war government sought to provide infants with a cod liver oil supplement.
The belief that foods rich in omega-3 fatty acids are good for us goes much further back than those days, however. The Greek physician Hippocrates wrote about using dolphin liver oil to treat skin conditions well over 2,000 years ago. Early Shetland islanders are reported to have used cod liver oil to treat “old pains”; shark-liver ointment was being used in the 1700s to treat rickets; and the English physician Thomas Percival had cod liver oil entered into the 1771 British Pharmacopoeia for the treatment of arthritis.
The modern interest in omega-3s dates back to a Danish study on the Inuit population of Greenland in the 1970s, when researchers Hans Olaf Bang and Jørn Dyerberg found the Inuits had lower rates of coronary heart disease than Danish populations. After analysing the diet of seven Inuits they suggested that this was because they were eating more of the omega-3 fatty acids found in marine sources like oily fish, algae and cod liver.
This led to an explosion of research into marine omega-3s. It was not long before it became a mainstay of supermarket labels, and the world’s expert agencies set recommended daily intakes for maintaining good health.
Yet the credibility of marine omega-3s took a knock in 2014 when Canadian cardiologist George Fodor co-published a scathing systematic review of the work by Bang and Dyerberg. He showed that the reason the Greenland hospital records showed what they had was likely because the Inuits lived so far away that their heart disease often went unreported. In fact, they had equivalent rates to their Danish counterparts.
Various overarching analyses into marine omega-3s have done further damage to their reputation as a treatment for specific diseases. These have shown marine omega-3 supplements to be largely ineffective in relation to heart disease, diabetes and protecting muscle mass in cancer patients. As for treating old pains and rickets, this is now widely attributed to the vitamin D in fish-oil products.
So where does this leave us? There may be legitimate reasons for omega-3 supplements being ineffective in some clinical trials. Not all supplements contain what they say on the label, as demonstrated by a 2015 study. That study and another found levels of toxic compounds exceeding international limits that could affect the results of clinic trials and yet are rarely if ever acknowledged in research.
In the case of heart disease, there may be another explanation. Where the damning analyses appeared to show there were no heart benefits from taking marine omega-3 supplements, a systematic review from 2006 of previous findings indicated these may have overlooked something important: you only need to eat about 300mg of marine omega-3s a day to maximise protection from heart disease. Because this amount is easy to achieve from food, the “control” group of people in a trial taking no supplements would – if they were eating oil fish – potentially respond no differently to the group who were taking the supplements.
There might be a similar mitigating factor over muscle-mass protection: those cancer patients in studies who are not meant to be taking omega-3 supplements but are aware of the benefits might sometimes distort the results by taking them anyway. Studies which have tried to control for this issue or better confirm compliance have reported largely positive effects.
Given these apparent benefits, researchers have wondered whether marine omega-3s might prevent the major societal problem of muscle wasting in older people. Where younger adults need to eat an optimal amount of high-quality protein per meal to help stimulate muscle growth, older people need a substantially higher dose because their muscles are resistant to the effects of protein. Research suggests that marine omega-3 supplementation may help lower that resistance. Further studies have shown that older people can also improve their skeletal-muscle function if they either take supplements for 90 days while weight training or for six months on their own.
These studies might have focused on older people, but they helped inspire a boom in young bodybuilders taking fish oil. Our research team at the University of Stirling recently investigated how marine omega-3s affected the muscle-growth response in this group when combined with protein and weight training. We found it didn’t make much difference, though admittedly our volunteers were consuming slightly more than the optimal amount of protein for muscle growth.
We still need to research whether omega-3 supplements might help young trainers consuming sub-optimal amounts of protein – for instance while cutting calories to make weight for weight-category sport. There are meanwhile increasing amounts of data indicating marine omega-3s may help other body functions important to sporting performance – immune and lung function, for example – but again these need to be more robustly confirmed in athletic populations.
So although the shine may have come off omega-3 fatty acids a little in recent years, there are still positives. As well as the possible mitigating factors around heart disease and cancer muscle wasting, previous findings demonstrating the importance of omega-3s for pregnancy and brain development still stand.
Ultimately these are nutrients that the body can’t make on its own. It therefore makes good sense for most of us to follow the official recommended intake of one portion of oily fish per week (140g when cooked contains about 250mg of omega-3). For older people seeking to protect muscles, the research suggests much more: 3g-5g of omega-3 per day. Since guidance also recommends against eating more than four portions of oily fish per week due to possible mercury toxicity, that’s best achieved through supplements. Where once it was our grannies that made us take cod-liver oil, it may be our turn to encourage them to consume it instead.