Fish oil not as good for pregnant mums as thought: Study

By Dr. Ananya Mandal, MDOct 19 2010

According to a new Australian study, taking fish oil / docosahexaenoic acid (DHA) supplements during pregnancy 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 researcher Maria Makrides, deputy director of the Women's and Children's Health Research Institute and professor of human nutrition at the University of Adelaide in Australia, “Our data suggest that there is no need for apparently healthy pregnant women to take DHA supplements.” The study is published in the Journal of the American Medical Association. A spokesperson for the supplement industry suggested weaknesses in the study.

There is a lot of literature that has shown 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 is believed that the DHA or docosahexaenoic acid in fish oil may be the reason for the benefit. Current guidelines also suggest that women eat an average of 200 milligrams of DHA a day during pregnancy.

For their study Makrides and her colleagues evaluated 2,320 women who were randomly given either three 500-milligram fish oil capsules (containing DHA) daily or three 500-milligram capsules of vegetable oil daily from the 21st week of pregnancy. After six weeks and six months of delivery they took a test on depression. Also 694 children at age 18 months were evaluated testing such developmental skills as sensorimotor development, memory, simple problem solving, and language.

Results showed six months after birth, the percent of women with high levels of depressive symptoms did not differ much between the two groups. While 9.6% of those taking DHA had high levels of depression, 11% of the mothers taking the vegetable oil capsules did. The difference was not statistically significant.

The women who already were suffering from depression were found to have a 3% or 4% reduction in symptoms. Makrides said, “It may be that these women will benefit from supplementation, but other studies are needed to confirm this.”

DHA supplementation however reduces the risk of 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.

When tested at 18 months, the average cognitive and language scores of the children did not differ between groups. Longer assessment of the children is on the cards. Makrides says. “We are already planning to assess all the children again at 4 years.”

Makrides is a part of the scientific advisory boards of Nestle, Fonterra (a dairy company), and Nutricia (a medical nutrition company).

Makrides concluded saying, “This is the largest and most well conducted study of its type… 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.”

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 feels that the results of the study are inconsistent with previous literature. He pointed out some weaknesses, “The timeliness of the intervention may be off.” He suggested 21 weeks of pregnancy may be too late to start the supplements to get benefits. Makrides' plan to assess the children later is a good one, he says.

Emily Oken, associate professor of population medicine at Harvard Medical School in Boston, who co-authored an editorial to accompany the study added that further work is needed. It could be that the Australian study did not include women most at risk of postpartum depression, she says. Till further evidence she says pregnant women are advised to take their supplements. “Most women can get [the recommended amount] by eating one or two fish servings a week of fattier fish, such as salmon or herring…If they can't or won't, it's reasonable and safe to take a supplement,” she added. “I think there are two things that are quite clear,” said Oken. “One is that it's safe to take fish oil supplements. The second is that they reduce the rate of preterm births.”