By Professor Wayne Cutfield
For years, women have been told that taking fish oils in pregnancy could boost their babies’ brain development.
In New Zealand, somewhere between 10 and 20 per cent of pregnant women now take fish oil supplements.
The problem is, there’s strong and growing evidence that fish oil supplements won’t make your baby smarter.
More worryingly, our new study published today suggests that we can’t rule out harmful effects from taking oxidised (“off”) fish oil supplements in pregnancy.
Female rats were given either unoxidised fish oil, a highly oxidised fish oil, or water (the control group) daily throughout pregnancy. It’s common practice in animal experiments to give a more potent formulation initially to determine if there is any effect, then vary the doses in subsequent studies. The dose we used is one commonly used in fish oil studies in rats.
We expected some negative health effects, because omega-3 fatty acids break down to toxic chemicals through oxidation. What we didn’t expect was that almost 30 per cent of the newborns in the oxidised group would die in their first two days of life – a mortality rate eight times that of the newborns in the control group – but that’s what we found.
Why would oxidised fish oil fed to pregnant rats cause their babies to die? We don’t know – because we didn’t anticipate this effect, we didn’t design our experiment in a way that would reveal mechanisms.
We hope to do future studies to examine what happens in pregnant rats when you vary how oxidised the fish oil is, and to understand exactly how the oxidised fish oil harms the baby rats.
Of course, if women could be confident that the fish oil supplements they buy in New Zealand aren’t oxidised, there would be no health concern.
But they can’t. Our earlier study, published in Scientific Reports in January 2015, tested 36 brands of fish oil supplements sold here. We used the international industry standard test of oxidation – the same one recommended by the Australian Therapeutic Goods Administration, WHO and the Food and Agriculture Organization of the United Nations.
From fish to capsule
There have now been five studies conducted in four continents that all show a very similar picture: retail fish oil is often oxidised beyond recommended levels at purchase. Clearly this is not a problem unique to New Zealand. All of these studies were conducted by independent researchers.
We found that 83 per cent were oxidised beyond international recommended levels. How “off” they were had nothing to do with best-before date, price, or the country of origin.
Omega-3 fatty acids are known to be chemically fragile or “unstable”, and can easily break down when exposed to natural conditions such as light, heat and oxygen. And the journey from fish to capsule can take 18 months.
We don’t want to cause undue panic. Oxidised fish oil is unlikely to carry serious health risks in humans – we haven’t seen a spike in birth complications or newborn conditions with the growing use of fish oil supplements.
But, at the moment, we just don’t know the health risks to the unborn baby. And there’s no way of knowing if the fish oil a pregnant woman takes is oxidised or not.
As medical researchers, we observe the axiom: “do no harm”.
On that basis, we recommend that, until further research determines the risk to humans, pregnant women shouldn’t take fish oil supplements.
Wayne Cutfield is Professor of Paediatric Endocrinology at the Liggins Institute, and an expert on insulin sensitivity and action in children. He leads clinical research which shows how environmental influences early in life can affect childhood growth and development in ways that could lead to chronic conditions in adult life. A former director of the Liggins Institute, he is now Interim Director of the National Science Challenge: A Better Start – a cross-institution research programme based at the institute.