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Childhood social class and cognitive aging in the Swedish Adoption/Twin Study of Aging

  1. Nancy L. Pedersena,d
  1. aDepartment of Medical Epidemiology and Biostatistics, Karolinska Institutet, 171 77 Stockholm, Sweden;
  2. bAging Research Center, Karolinska Institutet & Stockholm University, 171 77 Stockholm, Sweden;
  3. cInstitute for Gerontology, School of Health and Welfare, Jönköping University, 553 18 Jönköping, Sweden;
  4. dDepartment of Psychology, University of Southern California, Los Angeles, CA 90007;
  5. eDepartment of Psychology, University of California, Riverside, CA 92521

  1. Edited by Bruce S. McEwen, The Rockefeller University, New York, NY, and approved May 16, 2017 (received for review December 15, 2016)

Significance

There is a previously well-established relationship between socioeconomic status and cognitive ability. By having access to repeated measures of cognitive data across the second part of the life span, we were able not only to study the influence of childhood social class on mean-level cognitive performance, but also on change over time. Using reared-apart monozygotic and dizygotic twins and a control sample of twins reared together, we studied the effects of childhood socioeconomic environment on cognition in later life. We found an association between childhood social class and mean levels of cognitive performance, but not longitudinal trajectories of change. When controlling for genetic influences, there was no association of childhood social class and cognitive performance late in life.

Abstract

In this report we analyzed genetically informative data to investigate within-person change and between-person differences in late-life cognitive abilities as a function of childhood social class. We used data from nine testing occasions spanning 28 y in the Swedish Adoption/Twin Study of Aging and parental social class based on the Swedish socioeconomic index. Cognitive ability included a general factor and the four domains of verbal, fluid, memory, and perceptual speed. Latent growth curve models of the longitudinal data tested whether level and change in cognitive performance differed as a function of childhood social class. Between–within twin-pair analyses were performed on twins reared apart to assess familial confounding. Childhood social class was significantly associated with mean-level cognitive performance at age 65 y, but not with rate of cognitive change. The association decreased in magnitude but remained significant after adjustments for level of education and the degree to which the rearing family was supportive toward education. A between-pair effect of childhood social class was significant in all cognitive domains, whereas within-pair estimates were attenuated, indicating genetic confounding. Thus, childhood social class is important for cognitive performance in adulthood on a population level, but the association is largely attributable to genetic influences.

Footnotes

  • ↵1To whom correspondence should be addressed. Email: malin.ericsson{at}ki.se.

Freely available online through the PNAS open access option.

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