Will fish oil give us cancer?
People often feel frustrated when advice about what’s healthy changes.
Just when you think you’re doing the right thing, eating the right foods, maybe taking beneficial supplements, along comes a news report that makes it look like that was all wrong. The experts have ‘changed their minds’ again, leading us to conclude that we might as well not even try being healthy. “Everything will kill you!” people say.
Such was the case recently, when it was reported with some sensation that omega-3 fatty acids – those ‘good fats’ found in oily fish and fish oil supplements – rather than reducing the risk of disease, actually increase the risk of prostate cancer in men. A study published in the Journal of the National Cancer Institute reported that men with high concentrations of marine-derived omega-3s in their blood showed a 43 per cent higher risk of developing prostate cancer than those with the lowest levels.
On the surface, that sounds alarming. My husband told me he was going to stop taking his omega-3 supplement after seeing the news report. You might also conclude it’s a good idea to eat less fish.
However, it takes some digging into the detail to find the real story. What hasn’t been reported – and is seldom reported with stories like this – is that the study in question has since been widely criticised by scientists and cancer experts. That’s because they feel the researchers (and the news reports) overstated the evidence. The research was not good enough to say ‘omega-3s cause cancer’. For example, the researchers didn’t look at how the men in the study got their omega-3s – whether they got it from fish or from supplements, or at the different types of omega-3s present. No information was gathered about the rest of the men’s diets either, so we don’t know what else they were eating. Could some of the men be taking fish oil but not eating many fruits and veges? Eating lots of red and processed meat? We don’t know.
Critics also say that the difference between ‘high’ and ‘low’ levels of omega-3 quoted was just 0.2 per cent, and that both groups actually fall within the ‘normal’ range. Following the logic of the researchers’ conclusion, then, we should expect that populations with very high intakes of oily fish – such as Japan – should have “incredibly high” levels of prostate cancer, which they don’t. There was also criticism of the methodology used to get the omega-3 measurements, and the fact that this study was not actually designed to look at the relationship between omega-3s and prostate cancer; it was part of a larger study looking at other things.
So what’s the outtake here? It is tricky as a consumer to know what to think, especially with the way these kinds of things are reported in the news – it’s the nature of the news business to pick the most sensational aspect of any story. As lay people we shouldn’t have to go rummaging through academic journals to try and make head or tail of what we read in the paper.
My advice is that it’s prudent to pause any time you see a report on an issue of health like this, and ask: what does this actually prove? It’s really worth understanding that there’s a difference between association – which this study does seem to show – and cause and effect, which it really doesn’t prove at all. Interestingly, data from the same group also seemed to show that men who smoked and men who drank alcohol had lower risk of cancer than non-smokers and non-drinkers. Yet no-one is recommending starting smoking to avoid cancer.
When it comes to omega-3s, there has been and continues to be a lot of research into all sorts of areas. It’s probably fair to say that the evidence around the benefits of supplements is not conclusive. However, the benefits of eating fish and seafood are widely acknowledged. So our best bet, as is often the case, is to eat real food. Fish – especially oily fish like salmon and tuna – a couple of times a week is still a great idea.