The double-burden of poverty on cognition hypothesis: a systematic review of the mechanisms of the effect of poverty in early life on the development and expression of cognition in adolescence and adulthood.

Given the established detrimental effect of poverty in early life on later cognition, understanding the mechanisms underlying this relationship is important to design interventions to mitigate such inequities. However, eliminating inequities may not be enough. It is likely that poverty in early life is also associated with reduced qualification and job opportunities, in which case the benefit of healthy cognitive development could be mitigated or even neutralized. We referred to this potential effect of early poverty on both the development and expression as the double-burden hypothesis (DBH). This study systematically reviews the literature on the mechanisms by which childhood poverty can affect cognitive outcomes later in life and includes original studies that either quantified the role of mediators of the effect of early-life socioeconomic position (SEP) on cognition or that assessed whether early SEP modifies the relationship between later IQ and income. Of the 27 articles selected, all studied mediation and consistently identified educational attainment and adult SEP as key mediators. However, much of the available evidence is limited by retrospective measures, confounding, and selection bias. This suggests that while direct effects of childhood poverty might exist, most of its impact on later-life cognition operates through modifiable mechanisms. Reinforcing the importance of interventions that target early-life environments to reduce the long-term impacts of childhood poverty. Further studies with robust methods are needed to confirm these findings and provide more reliable estimates. Moreover, the present review shows that effect modification is an underexplored route to further develop effective, equitable interventions.