Aerobic fitness is associated with hippocampal volume in elderly humans

Abstract

Deterioration of the hippocampus occurs in elderly individuals with and without dementia, yet individual variation exists in the degree and rate of hippocampal decay. Determining the factors that influence individual variation in the magnitude and rate of hippocampal decay may help promote lifestyle changes that prevent such deterioration from taking place. Aerobic fitness and exercise are effective at preventing cortical decay and cognitive impairment in older adults and epidemiological studies suggest that physical activity can reduce the risk for developing dementia. However, the relationship between aerobic fitness and hippocampal volume in elderly humans is unknown. In this study, we investigated whether individuals with higher levels of aerobic fitness displayed greater volume of the hippocampus and better spatial memory performance than individuals with lower fitness levels. Furthermore, in exploratory analyses, we assessed whether hippocampal volume mediated the relationship between fitness and spatial memory. Using a region-of-interest analysis on magnetic resonance images in 165 nondemented older adults, we found a triple association such that higher fitness levels were associated with larger left and right hippocampi after controlling for age, sex, and years of education, and larger hippocampi and higher fitness levels were correlated with better spatial memory performance. Furthermore, we demonstrated that hippocampal volume partially mediated the relationship between higher fitness levels and enhanced spatial memory. Our results clearly indicate that higher levels of aerobic fitness are associated with increased hippocampal volume in older humans, which translates to better memory function.

Copyright 2008 Wiley-Liss, Inc.

Figures

FIGURE 1

Figural representation of the mediation model presented in this article. Aerobic fitness (IV) influences spatial memory performance (DV). Hippocampal volume is predicted to mediate this relationship. The proposed model hypothesizes that aerobic fitness causes an increase in hippocampal volume, which in turn causes an improvement in spatial memory.

FIGURE 2

Scatterplots showing that with an increase in fitness (VO2 peak) there is an increase in hippocampal volume (cm3). Correlations for both the left and right hippocampus with fitness remained significant even after including age, sex, and years of education as covariates.

FIGURE 3

In this bar graph, we represent on the Y-axis the variance (R2) in accuracy on the 3-item spatial memory task explained by each factor or combination of factors on the X-axis. A test of mediation examines whether controlling for the variance associated with hippocampal volume significantly reduces the variance in 3-item spatial memory associated with fitness. It is clear that the magnitude of the relationship between 3-item spatial memory performance and fitness is significantly reduced when left hemisphere volume was entered into the regression model thereby indicating a mediating relationship for the left hippocampus on the fitness-spatial memory relationship (P < 0.03).