Cognitive and Neural Correlates of Aerobic Fitness in Obese Older Adults

Abstract

Background/Study Context: Aerobic fitness is associated with preserved cognition and brain volume in older adulthood. The current study investigated whether the benefits of aerobic fitness extend to obese older adults, a segment of the population that is rapidly growing and who exhibit compromised cognition and brain structure relative to their nonobese counterparts.

Methods: Measures of obesity, aerobic fitness, cognition (processing speed, executive function, spatial ability, memory), and regional brain volumes (prefrontal gray, prefrontal white, hippocampus) were obtained from 19 obese older adults aged 65 to 75. Hierarchical linear regression analyses were conducted to examine the proportion of unique variance in cognitive and volumetric measures accounted for by aerobic fitness after controlling for covariates (age, gender, and waist circumference).

Results: Aerobic fitness accounted for a significant amount of unique variance in processing speed (adjusted R ² = .44), executive function (adjusted R ² = .34), and hippocampal volume (adjusted R ² = .27).

Conclusion: This novel pattern of results suggests that obesity does not preclude the benefits of fitness for cognition and brain volume in older adults. Fitness appears to be a beneficial factor for maintenance of processing speed, executive function, and hippocampal volume, which are vulnerable to age- and/or obesity-related decline.

Acknowledgments

This study was supported by NIH grants AG025501 (to D.T.V.) and DK56341 and UL1RR0224992 (Washington University Clinical Nutrition Research Unit and Clinical and Translational Science Award respectively). Julie Bugg was supported by National Institute on Aging grant 5T32AG00030. The authors thank Lindsay Casmaer, Marlisa Isom, and Tessa Mazzocco for assistance with this project.

Notes

Note: (1) VO_{2 peak} relative to ALM = VO2 _adjusted; (2) The mean maximum HR increases to 142 when 4 subjects taking beta-blockers or calcium channel blockers, which can lead to less reliable HR estimates, are removed.

¹There were two measures of obesity, BMI and waist circumference, in the present study. The measures were strongly correlated (r(17) = .82, p < .001). Therefore, we elected to treat one as a potential covariate rather than both so as not to restrict power. We chose waist circumference because of prior studies showing negative effects of this measure of obesity on cognition (West & Haan, 2009) and brain volume (Jagust et al., 2005), independent of BMI. Controlling for obesity (i.e., waist circumference) in the regression analyses permits one to conclude that any observed relationships between aerobic fitness and cognition or brain volume relate to varying degrees of fitness and not obesity, which has been shown in past studies to covary with fitness.

²The minimum sample sizes needed to observe a significant relationship between aerobic fitness and the following outcomes were computed based on a model in which power was specified at .80, three covariates and one predictor variable were included, and effect sizes were estimated to be equivalent to those obtained in the current study. Sample sizes were calculated for alpha levels of .01, .05, and .10, respectively: spatial ability (ns = 36, 25, 20); recollection estimate (ns = 132, 89, 70); familiarity estimate (ns = 65, 44, 35); prefrontal gray matter volume (ns = 84, 57, 45); prefrontal white matter volume (ns = 71, 48, 38). We thank an anonymous reviewer for suggesting the inclusion of these estimates.