Pregnant women have a lot to worry about when it comes to keeping their bodies and their developing babies healthy. Now researchers in Australia report that fish-oil supplements, a popular nutritional boost that many moms-to-be thought helped boost their mood and their little ones’ brain development, doesn’t do much for either.
In a study of more than 2,300 pregnant women at five Australian hospitals between 2005 and 2008, scientists found that those who took fish-oil supplements — mostly in the form of docosahexaenoic acid, or DHA, a breakdown product of the original fatty fish oil — had the same rates of postpartum depression as those taking a placebo. (More on Time.com: 5 Pregnancy Taboos Explained (or Debunked))
In addition, the children born to women taking DHA showed no significant improvements in cognitive development at 18 months compared with those born to women not taking the supplements.
The results contradict previous findings in population-based studies that asked women about their DHA consumption after giving birth; those studies showed that women who consumed higher levels of fish oil had a 6% to 7% reduction in depressive symptoms following delivery than those who ate less. But the current study’s findings are considered more reliable, since the investigators randomly assigned women to take either DHA or placebo and then observed rates of postpartum depression and measured childhood development markers such as language and other cognitive skills.
The fact that the trial did not find any mood or cognitive benefits to the fish-oil supplements, however, doesn’t mean that women should stop eating fish or stop taking fish-oil supplements. The authors did find one positive correlation, and that was between DHA use and a lower risk of preterm birth, before 34 weeks (doctors consider 39 weeks full term). “There is no strong evidence supporting the benefits of these supplements,” says Dr. Emily Oken, a professor of population medicine at Harvard Medical School, who wrote an editorial accompanying the paper in the Journal of the American Medical Association. “But my personal advice as a physician and mother is I encourage people to try to eat fish lower in mercury and higher in DHA, such as salmon, trout, herring and anchovies. Eating one or two servings of these fish a week will get women their recommended intake of DHA of 200 mg per day.” (More on Time.com: Photos: Pregnant Belly Art)
Although this particular study did not find any benefits for postpartum depression, Oken notes that about a third of the women who initially signed up for the trial were ineligible because they were already consuming the recommended amount of DHA. These women may have been supplementing their diet with the fish oil already because they were at higher risk of depression, and she says that these women may be the ones to benefit most from higher doses of DHA — in the study, the volunteers were taking 800 mg daily.
And with respect to fish oil’s benefits for cognitive development in children, other smaller studies found that the effects of gestational DHA exposure may not show up in toddlers until they are several years old, when language skills are more established.
While the new study may discourage pregnant women from supplementing their diet with fish oil, Oken notes that there are other known benefits of the oil, such as protection from heart disease, as well as the possibility that it may still improve cognitive development in older kids. “I don’t think women should feel like they are harming their children if they chose not to eat fish or include fish in their diet,” she says. “But at the same time, we as physicians and public health officials could do a better job in letting women know that they can reasonably consume fish while they are pregnant without worrying about mercury.”
At the very least, she says, women should continue to aim for consuming at least the recommended 200 mg a day. The study did not show any harm from that, and it could help prevent preterm births, which can put the baby and mother at risk of additional health problems.
More on Time.com: