Differing Effects of Education on Cognitive Decline in Diverse Elders with Low Versus High Educational Attainment

Educational attainment is a key component of successful cognitive aging and a major protective factor in dementia (Stern, 2009). Recently, there has been growing debate over whether and how early-life educational experiences alter late-life cognitive trajectories. As summarized by Antsey & Christensen (2000), many studies published in the 1990's analyzed two occasions of measurement and documented an association between more years of education and attenuated rates of late-life cognitive decline (Albert et al., 2995; Arbuckle, Maag, Pushkar & Chaikelson, 1998; Butler, Ashford & Snowdon, 1996; Evans et al., 1993; Farmer, Kittner, Rae, Bartko & Regier, 1995). As summarized by Zahodne et al. (2011), more recent studies using three or more occasions of measurement and growth curve modeling have failed to identify this association (Christensen et al., 2001; Karlamangla et al., 2009; Tucker-Drob, Johnson & Jones, 2009; Van Dijk, Van Gerven, Van Boxtel, Van der Elst, & Jolles, 2008; Wilson et al., 2009; Piccinin et al., 2013). In explaining these discrepant results, researchers have highlighted analytic differences across studies (Zahodne et al., 2011; Piccinin et al., 2013). For example, many early studies using regression-based approaches conditioned on the baseline measure of cognition. Conditioning on baseline cognitive level has been shown to produce biased effect estimates when the variable of interest is strongly related to baseline cognitive level, as is certainly the case with years of education (Glymour et al., 2005). Piccinin et al., (2013) recently addressed the issue of analytic variability in the literature by reporting results from six independent longitudinal studies of aging using a common analytic approach (i.e., growth curve model with time-in-study time basis) with a common set of predictors (i.e., age, sex, years of education) centered at common values. In that study, no association between education and cognitive decline was found for four out of the six studies. In contrast, higher education was associated with slower rates of cognitive decline in the Origins of Variance in the Oldest-Old dataset (Cederlof & Lorich, 1978; Pedersen, Lichtenstein & Svedberg, 2002), which featured relatively low average education (i.e., 7 years). Finally, education near the median (11 years), but not additional years, was associated with slower cognitive decline in the Canberra Longitudinal Study dataset (Christensen et al., 2004). These results present the intriguing possibility that only early education influences late-life cognitive trajectories, whereas additional years of education beyond some minimum confer no additional protection. For example, Lyketsos, Chen, and Anthony (1999) have proposed that additional education beyond nine years is not associated with additional reduction in cognitive decline. Another issue regarding the association between education and late-life cognitive decline that has been relatively overlooked by the epidemiologic literature relates to potential mechanisms. For example, education may influence later-life cognitive trajectories by promoting aspects of cognitive and neural development during a sensitive period of childhood that protect against late-life cognitive decline. Another (non-mutually exclusive) possibility is that educational attainment sets an individual up for a lifetime of advantageous experiences, both cognitive (e.g., cognitively-demanding occupation and leisure activities) and non-cognitive (e.g., higher income, better quality neighborhoods, increased access to high-quality healthcare). The overall goal of this study was to more thoroughly investigate the relationship between education and the rate of late-life cognitive decline in a racially, ethnically, and educationally diverse population. Specific aims were to: (1) quantify the relationship between years of education and late-life cognitive decline; (2) determine whether years of education is only associated with late-life cognitive decline among individuals with relatively lower education; and (3) test whether associations between education and late-life cognitive decline are independent of or driven by lifetime advantage, as defined by late-life income.