Long-chain omega-3 fatty acid supplementation for pregnant or breastfeeding women had no strong effect on their children’s cognition or birthweight[5]
What was studied? The cognition and birthweight of children whose mothers supplemented fish oil while pregnant or breastfeeding, through meta-analyzing randomized, controlled trials.
Why study it? The long-chain omega-3 polyunsaturated fatty acids found in fish oil, especially docosahexaenoic acid (DHA), have been shown to be essential in learning and memory in primate experiments, and in neuronal development in other animal experiments. However, whether supplementation will help the cognition of developing human minds is still an open question.
What was(n’t) found? There was no statistically significant effect on any cognitive measure or birthweight.
How null was it? The result was not strongly null for three big reasons. The first was that most of the trials were small and had large dropout rates, making it difficult to see even moderate effects in many cases. Second, supplementation would probably have the greatest effect before 20 weeks of gestation, but none of the examined trials started supplementation that early (although this is a big logistical challenge and would be hard to do practically). Finally, while there were no statistically significant effects observed, the 95% confidence intervals suggest that the data were mostly compatible with small effects on attention and birthweight. Thus, there may be some small effect in these two domains.
DHA supplementation didn’t have a big effect on the executive function of school-aged children[6]
What was studied? The effect of 300 milligrams of daily docosahexaenoic acid (DHA) supplementation on school-aged children’s executive function, which is the ability to exert self-control, shift focus consciously, and process information.
Why study it? DHA accumulates in parts of the brain that develop rapidly in childhood through mid-adolescence and are important for executive function. DHA levels in certain parts of the brain have also been found to be associated with stronger brain activation. However, it’s still unclear whether supplementation with DHA could actually improve functioning in school-aged children.
What was(n’t) found? No effect on any metric of executive function, including cognitive flexibility and working memory, was found.
How null was it? The trial was well designed and preregistered with a clear primary outcome. However, the dose may have been too small or the time frame too short to see a clear effect. Confirmation of these results at higher doses with a wider battery of cognitive tests for confirmation may be helpful.
Zinc supplementation, both with and without iron co-supplementation, has no clear effect on childhood motor or mental development[7]
What was studied? Randomized controlled trials exploring the effect of zinc supplementation on development metrics in children up to 5 years old were meta-analyzed.
Why study it? Zinc is important for neuronal development, but about 7.5% of children in high-income countries and over 50% in lower-income countries may be zinc deficient. However, zinc can lower iron blood levels because the two elements interfere with each others’ absorption.
What was(n’t) found? No measure of childhood motor or mental development was strongly affected by zinc supplementation, whether or not it was co-administered with iron.
How null was it? The authors were unable to meta-analyze trials in which the children were older than one year due to major differences between the studies they found. They rated the quality of evidence for zinc’s effect on children under one year as being low to moderate. However, it was harder to evaluate zinc’s longer-term impact, although they did assess the longer-term data qualitatively and found no major effect.