Caution advised over fish oil in pregnancy

Omega-3 is recommended in pregnancy, but new research suggests care is needed to avoid oxidised fish oil.

Dr Ben Albert suggests, in light of his team’s research, fish oil should be stored in cool, dark places.

A group of scientists from the University of Auckland’s Liggins Institute is sounding a warning after new research finding highly oxidised fish oils may be harmful in pregnancy.

Fish oil goes off or ‘oxidises’ very easily. The researchers wanted to find out whether there could be negative health effects from oxidised oils, in particular, whether they could be harmful in pregnancy.

 Pregnant rats were given fish oil in a range of doses and levels of oxidation, plus a control. See American Journal of Physiology: in press; 2022.

It would not be possible to do this research in humans, so an animal-based study was conducted, according to strict legislative and ethical protocols.*

All the animals appeared healthy during pregnancy, says Dr Ben Albert.  However, in a group which received human-relevant doses of highly oxidised oil, six percent of the offspring died.

In a 2015 study by Liggins researchers, of 32 fish oil products on store shelves, one was around this level of oxidation and the other products were less oxidised (see section below)

 In the newly published trial, fish oils within recommended levels of oxidation, when given at human-relevant doses, did not cause any harm to the offspring.

“This research tells us is that women who are pregnant should avoid highly oxidised fish oil and should do what they can to make sure that the fish oil they take stays unoxidised,” Albert says.

“Around the world, few products on store shelves seem to be oxidised above the levels that we have now shown to be safe in rat pregnancy. But it’s also important to prevent fish oil supplements from going off at home.”

The Ministry of Health recommends women eat oily fish to get their omega-3, but fish oil supplements are a popular option.

“If you choose to take fish oil, buy small containers rather than large ones, and store them in dark and cool places, like the fridge.”

The authors would like to see regulation of fish oils, with oils tested by an independent agency and shown to be within the recommended levels of oxidation before they’re sold.

Earlier research suggests half fish oil products oxidised

In 2015, Liggins Institute research showed most fish oil capsules sold in New Zealand had omega-3 fatty acid levels below those indicated on the label.

The researchers carried out detailed analysis of EPA and DHA content and degree of oxidation of fish oil capsules marketed in New Zealand.

Their results showed that only three of the 32 products tested contained the concentrations listed on the label while over half exceeded the recommended levels of oxidation products.

In addition, they found these measurements were unrelated to “best-before” dates, price or country of origin (Nature: Scientific Reports, 21 January 2015).