Fish oil during pregnancy – benefits questioned

New research led by the University of Adelaide challenges advice that pregnant women should increase their intake of fish oil. The study, published today in the Journal of the American Medical Association (JAMA), found that consumption of fish oil during pregnancy did not decrease post-natal depression or improve cognitive and language development in offspring during early childhood.

A copy of the paper and press release are available.

To follow up with New Zealand experts on the topic, contact us on 04 499 5476. Our colleagues at the AusSMC have rounded up the following commentary:

Dr Peter Clifton, Baker IDI Heart and Diabetes Institute; Affiliate Professor in the Department of Medicine at the University of Adelaide, comments:

“This excellent large study appears to settle the debate about whether pregnant women should supplement with DHA-rich oils, and like the post menopausal hormone interventions of the past decade show that epidemiology only provides clues that need to be pursued in rigorous clinical trials and cannot be relied on for making recommendations. So much of the apparent benefit of certain nutrients seen with epidemiology are due to behavioural confounders, no matter how well adjusted the study may be. The authors are to be congratulated on a great study and a clear paper.”

Dr Natalie Sinn, Research Fellow at the University of South Australia’s Sansom Institute for Health Research, comments:

“The trial is well conducted and rigorously designed, and with a large sample size which gives a lot of confidence in the findings. The results do not support those of previous studies implicating omega-3 fatty acids for depression and infant brain development. However I think that some very important caveats need to be made.

“With regard to depressive symptoms, the sample did not focus on women who had depression and so cannot necessarily be generalised specifically to women who have or are at risk of clinical postnatal depression. Studies that have indicated improved depressive symptoms (not post-natal depression) have been conducted with clinically depressed samples.

“More importantly, with regard to developmental outcomes, psychological assessments are notoriously hit-and-miss when it comes to detecting nutritional influences, and particularly global tests as were used in this study. We cannot conclude from this study that DHA did not assist infant cognitive development, only that it did not influence performance on the selected tests. Indeed, a couple of notable, well-designed omega-3 studies found highly meaningful real-life outcomes (improved literacy in underperforming children and reduced reprimands for violent behaviour in juvenile offenders) that were not detected in psychological assessments that were used in those studies.

“Therefore we need to be very cautious about drawing any firm conclusions from these results. Given the established importance of DHA for brain structure, development and function, coupled with the low intake of the Australian population, I believe we have to be very careful about advising women that they do not need to take DHA in pregnancy based on the results.”

Comments from the authors of the research:

Professor Maria Makrides is lead author of the paper and a Professor of Human Nutrition in the Discipline of Paediatrics at The University of Adelaide:

“We undertook a large randomised controlled trial to determine whether increasing DHA during the last half of pregnancy will result in fewer women with high levels of depressive symptoms and enhance the neurodevelopmental outcome of the children and found that supplementation with DHA during pregnancy does not lower levels of postpartum depression in mothers or improve cognitive and language development in their offspring during early childhood.

“The trial involved 2399 women who were randomly allocated to a DHA-rich fish oil or vegetable oil capsules from about 20 weeks of pregnancy until birth. Post partum depression was assessed at 6 week and 6 months after the birth of the baby and the development of children was measured at 18 months.

The study involved five centres around Australia.”

Associate Professor Barbara Meyer is an author of the paper, which she worked on as part of the DOMInO Investigative Team. She is an Associate Professor in the School of Health Sciences and Director of the Metabolic Research Centre at the University of Wollongong:

“We conducted this trial as we believed that supplementation with DHA in the last trimester of pregnancy would reduce the risk of maternal post-partum depression and improve cognitive development in the offspring, however, the DOMInO trial outcomes did not support this. Our data showed that there was no difference in high levels of depressive symptoms during the first 6 months postpartum in the DHA group (9.7%) and control groups (11.2%) (Table 2 in paper). But this result needs to be taken into context and as explained in the paper, the lower than expected rate (16%) of women with high levels of depressive symptoms in the control group (11.2%) may be explained by simply taking part in a trial (i.e. interacting with people/researchers) can help prevent depressive symptoms (page 1681 in paper). The DHA supplemented group also tended to have (as it did not reach statistical significance) fewer new medical diagnosis of depression during the study period (Table 2). Furthermore, although not significant, these results may be more applicable to women with previously diagnosed depression because of the higher prevalence (20-26%) and also the higher absolute effect size (page 1681 in paper), and therefore further studies should be conducted in women with a history of depression.

“As this is the first study of its kind to be reported and other countries are currently conducting similar trials, it would be interesting to see their outcomes, especially if their women in the control group have a higher prevalence of women with high levels of depressive symptoms.”