One of the reasons breastfed infants may have better cognitive and visual development is because human milk contains long-chain, polyunsaturated fatty acids like the omega-3 DHA, while most available infant formulas do not, based on data I discuss in my video Should Pregnant and Breastfeeding Women Take DHA?. Infants given control formula without DHA didn’t do as well as those given DHA-fortified formula, and neither group did as well as the breastfed infants, who serve as the “gold standard.” This was enough to convince formula manufacturers to start adding DHA to their infant formula starting back in 2002.

The question then became how much to add? Easy, right? Just add the amount that is naturally found in breast milk. However, the DHA level in breast milk is extremely variable depending on what the mom is eating. There are a number of healthy populations who don’t eat any seafood, for example, and they have much lower levels in their milk yet seem fine. So this makes it difficult to determine the optimal amount to add to formula or, for that matter, what to recommend for pregnant and breastfeeding women. “Consensus guidelines recommend that women should aim to consume an average of 200 mg” of DHA daily during pregnancy. “Simply encouraging pregnant women to eat more fish is not so simple, because most fish are to some extent contaminated” with toxic pollutants, such as mercury. (See my video Mercury vs. Omega-3s for Brain Development for more on this.) For most fish, such as tuna, the brain damage caused by the mercury would exceed the benefit from the DHA.

Additionally, some pollutants, like PCBs, can get stuck in our bodies for decades, so it’s not enough to just eat clean during pregnancy.

What about purified fish oil? The methods supplement manufacturers use, like distillation, leave considerable amounts of PCBs and other pollutants in the products, so much so that when taken as directed, salmon, herring, and tuna oils would exceed the tolerable daily intake of toxicity.

Thankfully, one can get the benefits without the risks by getting DHA from algae instead, which is where the fish eventually get it from themselves. So, pregnant and breastfeeding moms can cut out the middle-fish and get DHA directly from the source—at the bottom of the food chain where we don’t have to worry about toxic pollutants.

Until recently, we thought everyone should take these long-chain omega-3s for their heart. However, the balance of evidence is now such that doctors “should not recommend fish oil intake or fish consumption solely for the primary or secondary prevention of CHD,” coronary heart disease. But what about for expectant and breastfeeding mothers? What does the latest science show? Putting all the studies together, it turns out adding DHA to formula does not appear to help infant cognition after all, similar to other recent compilations of evidence that show “no significant benefit.” In fact, at least four meta-analyses, or systematic reviews, have reached a similar conclusion. These were based mostly on the standard series of measurements known as the Bayley Scales for Infant Development. If other tests were used, would there be different results? So far, no. Giving women DHA supplements during pregnancy did not appear to help with other outcomes, like attention span or working memory, either.

Although there may be no significant benefit to infant cognition, what about other things like vision? Six trials have been done to date supplementing pregnant women. Four showed no effect, and the two trials that showed benefit had some problems. So, while we really don’t know at this point, if all the studies so far show either nothing or benefit, why not just take them to err on the side of caution?

There may not be any demonstrable “clear and consistent” benefits, but there are new studies on this coming out all the time. If it’s harmless, maybe women should just take it to be on the safe side? The problem is that it may not be harmless in large doses. In a study in which women were given a whopping 800mg of DHA a day during pregnancy, infant “girls exposed to higher-dose DHA in utero [in the womb] had lower language scores and were more likely to have delayed language development than girls from the control group.”

So, the “absence of clear positive effects and the possible presence of negative effects in the children raise the question whether DHA supplementation is justifiable…” But it was a really large dose, suggesting that there may be “an optimum DHA level below and above which DHA might be detrimental to the developing brain.”

So, maybe too much is detrimental, but what about too little? I discuss that in Should Vegan Women Supplement with DHA During Pregnancy.

Other videos on the concerns about the pollutants in the aquatic food chain include:

For more on fish oil, see:

In health,

Michael Greger, M.D.