Change in BMI and cognition in middle-aged and older adults : the Seattle longitudinal study

Abstract

Prior literature on the relationship between Body Mass Index (BMI) and cognition has been inconsistent. Thus, these relationships were examined in 1,023 participants (54.5%female) from the 1998 and 2005 waves of the Seattle Longitudinal Study (SLS). Participants were divided into two groups for the purpose of comparison, a middle-aged group (n=587; Age Range=40-64 years) and an older adult group (n=436; Age Range=65-93 years). The SLS records cognitive data in six abilities. Health variables included BMI, hypertension and smoking. Hierarchical multivariate regression analyses were used to examine relationships amongst change in BMI, cognition, hypertension, and smoking at both time points. Mean BMI for the study sample did not significantly change over time, but had a significant impact on predicting change in cognitive factor scores. A reduction in performance for change in verbal memory was identified with increased change in BMI for middle-aged adults, and an improvement in performance with change in verbal memory and change in spatial orientation with decreased change in BMI for older adults were found. Hypertension was not a significant mediator of the BMI- cognition relationships. However, smoking status was found to be a full mediator of the BMI-cognition relationship. Previous smoking at some time in the past explained the association between change in verbal memory and BMI over a seven-year period. The implications of this study yield new contributions to how increased BMI can negatively influence change in cognitive function in midlife adults, and how this association may change in older adulthood.