Pregnant women who take omega-3 supplements in the belief it will give their babies a brain boost might want to reconsider, says a new study, which found no cognitive edge among children whose mothers took the supplements.
Docosahexaenoic acid, or DHA, is one of three omega-3 fatty acids thought to support growth of a baby's brain and tissues.
It is most commonly found in fish, but increasingly it's being marketed to pregnant women in the form of prenatal supplements. A search on Amazon.ca yields more than 40 results, many touting benefits for a baby's brain development.
"Use of these supplements has become common in developed countries, but the effects of DHA have been unclear," said the study's lead author, Jacqueline Gould, a child nutrition researcher with the South Australian Health and Medical Research Institute.
To test the effect, her team gave one group of mothers 800 milligrams of DHA daily during the last half of pregnancy. The other group was given a placebo.
In the latest study, researchers followed up with more than 500 of those mothers' children at age seven and tested them for a variety of developmental outcomes, including IQ, language, academic abilities, and executive functions such as memory and problem solving.
They found no difference between the two groups, besides slightly higher perceptual reasoning among those born to mothers who received DHA supplements. The results mirrored those found when the children were tested at age four.
"Our findings do not suggest that the DHA supplements caused benefit or harm for child development," Gould said.
Best to get it from food
"It's a good reminder to be wary of misinformation or all that marketing which goes into selling supplements that may not be necessary," said Jennifer House, a registered dietitian in Calgary.
Instead, House says it's always best to get omega-3 fatty acids like DHA from food such as salmon or trout, because they contain other nutrients including vitamin D, zinc, and iron.
Dietitians of Canada, as well as Health Canada, recommend that pregnant women eat 150 grams, or two servings the size of a deck of cards, of cooked fish each week.
For those who are concerned about mercury, Health Canada provides guidelines on which fish to avoid, like tuna, shark, and swordfish. But it says "the benefits of eating fish are greater than not eating fish, when pregnant women choose the recommended types and amounts."
House adds that a standard prenatal multivitamin, which includes folic acid and iron, should be enough for most women.
DHA might have other benefits
Ken Stark, an associate professor who studies omega-3 fatty acids at the University of Waterloo, says one of the challenges of this study is that it doesn't include information on the mothers' diets during pregnancy.
He points out that researchers tested the level of DHA in the blood of newborns' umbilical cords, and found that even the babies from mothers who didn't take supplements had relatively normal levels of DHA, suggesting the mothers were likely consuming enough of the fatty acid.
He also says animal studies have shown the brain is relatively good at retaining levels of DHA compared with other tissues, something he calls the "brain effect."
"It doesn't look like the control group in this original study were really that low in omega-3, and once you get that and the brain effect, if you're not really low [in DHA] then you're really not going to see much improvement with extra DHA," he says.
But he notes that DHA can have other benefits beyond brain development. He recently co-authored a study that found fish oil supplements reduced a baby's risk of developing asthma. Other research has found that DHA supplements can reduce the risk of pre-term births.