Background Recent estimates suggest that dementia incidence is decreasing in the US possibly due to better management of cardiovascular disease (CVD) risk factors, but these studies lack repeated cross-sectional assessment among a representative US sample. Our objective was to assess temporal trends in cognitive performance in relation to CVD risk factors among older National Health and Nutrition Examination Survey (NHANES) participants.
Methods We used repeated cross-sectional assessment of 5711 participants ≥60 years of age from four NHANES cycles: 1999–2000, 2001–2002, 2011–2012 and 2013–2014. Cognitive function was assessed during each cycle with the Digit Symbol Substitution Test (DSST). We estimated mean DSST score at each cycle and annual trend in DSST before and after adjustment for age, sex, race/ethnicity, education, smoking status, blood pressure, glucose status and body mass index.
Results DSST scores was significantly higher for 2011–2012 (difference: 6.7, 95% CI 4.4 to 9.0) and 2013–2014 (difference: 6.2, 95% CI 4.0 to 8.5), but not 2001–2002 (difference: 2.3, 95% CI −0.01 to 4.6) as compared with 1999–2000 before adjustment. We observed a linear trend for higher annual DSST score before adjustment (DSST/year: 0.44, 95% CI 0.31 to 0.57) and after adjustment for age, sex, race/ethnicity, educational attainment and CVD risk factors (DSST/year: 0.17, 95% CI 0.08 to 0.26). Educational attainment was most strongly associated with the attenuation in the trend in cognitive function (77% of trend attenuation and 20% of variance in DSST).
Conclusion Cognitive function is improving over time for US adults aged ≥60 years. These improvements are strongly associated with greater educational attainment and irrespective of the changing US demographic and cardiovascular health profiles.
- cardiovascular disease risk factors
- epidemiological methods
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Contributors MB had full access to the data in this analysis. As such, he is the guarantor of this work, takes responsibility for the integrity of the data and the accuracy of the data analysis and affirms that the manuscript is an honest, accurate and transparent account of the study being reported. All authors made substantial intellectual contributions participating in creating and designing the study, analysing and interpreting the data and reviewing this manuscript.
Funding MB was supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health under Award Number T32HL069771 to conduct the current work while at Northwestern University in Chicago, Illinois, USA. AA was supported by the NHLBI of the National Institutes of Health under Award Number U01HL096902.
Disclaimer The views expressed in this manuscript are those of the authors and do not necessarily represent the views of the NHLBI; the National Institutes of Health or the US Department of Health and Human Services. MB has presented a preliminary version of this work as a poster at the American Heart Association Scientific Sessions in Chicago, Illinois, USA, in November 2018.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.