Oct. 19, 2010 -- Taking fish oil (DHA) supplements during pregnancy, widely thought to help mothers' moods and children's cognitive skills, does not appear to reduce the risk of postpartum depression of mothers or boost the language development and cognitive skills of their children, according to a new Australian study.
''Our data suggest that there is no need for apparently healthy pregnant women to take DHA supplements," says researcher Maria Makrides, PhD, deputy director of the Women's and Children's Health Research Institute and professor of human nutrition at the University of Adelaide in Australia.
She also found no differences in cognitive and language skills of the infants at 18 months, whether their mothers took DHA supplements or did not.
However, a spokesperson for the supplement industry sees weaknesses in the study.
The study is published in the Journal of the American Medical Association.
DHA, Moms, and Infants
In the past few years, studies in Europe and the U.S. have found that higher intakes of fatty acids known as n-3 long-chain polyunsaturated fatty acids (LSPUFA) from fish and seafood during pregnancy are linked with a reduced risk of symptoms of depression in mothers after they give birth and an improvement in children's language and cognitive skills.
It's believed that the DHA or docosahexaenoic acid in fish oil may be the reason for the benefit.
Expert guidelines recommend that women eat an average of 200 milligrams of DHA a day during pregnancy, although most women in the U.S. and other countries eat very little fish and don't get enough DHA.
Studies of DHA's effect in human pregnancies have yielded mixed results, Makrides says.
DHA and Depression: A Closer Look
Makrides and her colleagues evaluated 2,320 women randomly assigned from the 21st week of pregnancy on to take either three 500-milligram fish oil capsules (containing DHA) daily or three 500-milligram capsules of vegetable oil daily.
The mothers took a standard test about depression symptoms at six weeks and six months after delivery.
The researches evaluated 694 children at age 18 months, testing such developmental skills as sensorimotor development, memory, simple problem solving, and language.
At six months after birth, the percent of women with high levels of depressive symptoms did not differ much between the two groups, Makrides found. While 9.6% of those taking DHA had high levels of depression, 11% of the mothers taking the vegetable oil capsules did.
In the subgroup of women who had a previous history of depression, they found a 3% or 4% reduction in symptoms, she says. "It may be that these women will benefit from supplementation, but other studies are needed to confirm this," she says.
The mothers taking DHA did have fewer preterm births before 34 weeks' gestation. While 1% of the DHA mothers had a baby before 34 weeks, 2.25% of those in the vegetable oil group did. However, more of the DHA mothers went over the due date enough to require interventions such as induced labor or cesarean deliveries.
When tested at 18 months, the average cognitive and language scores of the children did not differ between groups.
It could be that a longer-term assessment is needed, Makrides says. "We are already planning to assess all the children again at 4 years."
Makrides reports serving on the scientific advisory boards of Nestle, Fonterra (a dairy company), and Nutricia (a medical nutrition company).
DHA and Effects: Industry Speaks
The study findings are inconsistent with those of many previous studies, says Duffy MacKay, ND, vice-president of scientific and regulatory affairs for the Council for Responsible Nutrition in Washington, D.C., a trade association representing manufacturers and ingredient suppliers of dietary supplements.
He also sees some weaknesses in the study. "The timeliness of the intervention may be off," he says, explaining that starting the supplements earlier than 21 weeks may have been better.
Some researchers question whether the most valuable nutrient for depression is DHA or another fatty acid, EPA. So knowing the levels of both EPA and DHA in mothers and infants would have been good information, he says.
Makrides' plan to assess the children later is a good one, he says.
His advice on DHA and EPA? "Make sure you get these nutrients, whether getting them from food or supplements."
DHA During Pregnancy: Conclusions
''This is the largest and most well conducted study of its type," Makrides says, "so we have a conclusive result about the fact that there is little or no effect of DHA supplementation during normal pregnancy on postpartum depression or early childhood neurodevelopment."
She does concede that further work is needed to determine the benefits of DHA for women with a history of depression or those at risk of delivering prematurely.
DHA During Pregnancy: Second Opinion
The final word is not yet in, says Emily Oken, MD, MPH, associate professor of population medicine at Harvard Medical School in Boston, who co-authored an editorial to accompany the study. She writes that the topic requires more investigation, including additional trials such as the Australian one.
It could be that the Australian study did not include women most at risk of postpartum depression, she says.
Until more study is done, Oken says, she advises pregnant women to get the recommended 200 milligrams a day of DHA, preferably by eating fish low in mercury and high in DHA.
"Most women can get [the recommended amount] by eating one or two fish servings a week of fattier fish, such as salmon or herring," she says. "If they can't or won't, it's reasonable and safe to take a supplement."