Turns out materialism is pretty tightly correlated with self-esteem:
We examine age differences in materialism with children and adolescents 8–18 years old. In study 1, we find materialism increases from middle childhood to early adolescence and declines from early to late adolescence. Further, we find that age differences are mediated by changes in self‐esteem occurring from middle childhood through adolescence. In study 2, we prime self‐esteem to obtain further evidence of a causal link between self‐esteem and materialism. As expected, we find that inducing high self‐esteem decreases expressions of materialism. Inducing high self‐esteem reduces materialism among adolescents so dramatically that age differences in materialism disappear.
Source: “Growing up in a Material World: Age Differences in Materialism in Children and Adolescents” from “Journal of Consumer Research”
Yeah, the study was done on adolescents but I’d be surprised if it wasn’t very applicable to adults as well.