 One of the reasons breast-fed 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 did not, based on data like this, where infants given control formula without DHA didn't do as well as those given DHA fortified formula. Neither did as well as the breast-fed infants who serve as the gold standard. But 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 however much is naturally found in breast milk. However, the DHA level in breast milk is extremely variable, depending on what the mom is eating. For example, there's all these healthy populations that don't eat any seafood and have much lower levels in their milk, and they seem fine, so that 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 milligrams a day of DHA during pregnancy. Of course, this isn't as simple as encouraging women to eat more fish because of the toxic pollutants, such as mercury, such that for most fish, such as tuna, the brain damage caused by the mercury would exceed the benefit from the DHA. And some pollutants like PCBs can get stuck in our bodies for decades, and 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 product, so much so that, 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 get it from, and 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. But until recently, we thought everyone should take these long chain omega-3s for their heart, but the balance of evidence is now such that doctors should no longer be recommending fish oil intake or fish consumption solely for prevention of coronary heart disease. But what about for expectant and breastfeeding mothers? What's the latest science show? Put all the studies together and turns out, adding DHA to formula does not appear to help infant cognition after all, similar to other recent compilations of evidence that showed no significant benefit. In fact, at least four meta-analyses or systematic reviews have reached a similar conclusion. Now, these were mostly based on a standard series of measurements known as the Bailey scales for infant development. Maybe if other tests were used, there'd be different results. But so far, no luck, given 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 benefits for 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 that showed benefit had some problems. And so we really don't know at this point. But hey, if all the studies so far show either nothing or benefit, why not just take them on the side of caution? Yeah, no demonstrable clear and consistent benefits, but there's 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 800 milligrams of DHA a day during pregnancy, infant girls exposed to the higher dose DHA in the womb had lower language scores and were more likely to have delayed language development than girls from women in the control group. So the absence of clear positive effects, along with the possible presence of negative effects, and the children raised the question whether DHA supplementation is justifiable. But it was a really large dose, suggesting that there may be an optimal DHA level below and above which DHA might be detrimental to the developing brain. So maybe too much is detrimental. What about too little? I'll cover that next.