A new study at Columbia University Mailman School of Public Health, and the Robert Butler Columbia Aging Center and Université Paris-Dauphine—PSL, found that having three or more versus two children has a negative effect on late-life cognition. The results further indicated that this effect was strongest in Northern Europe, where higher fertility decreases financial resources but does not improve social resources in this region. This is the first to study the causal effect of high fertility on late-life cognition.