Author Affiliation: Department of Kinesiology, University of Waterloo, Sunnybrook Research Institute, Waterloo, Ontario, Canada.
My colleagues and I thank Dr Smith for his interest in our article.1 Dr Smith raises the possibility that cardiorespiratory fitness may mediate the relationship between activity energy expenditure (AEE) and cognitive impairment. Though physical activity is 1 predictor, AEE itself is only weekly associated with cardiorespiratory fitness.2 As a result, other mechanisms such as alteration in brain-derived neurotrophic factor levels and improvement of vascular function are likely to contribute to the relationship.3
Middleton LE. Physical Activity, Vascular Health, and Cognitive Impairment—Reply. Arch Intern Med. 2012;172(1):83-84. doi:10.1001/archinternmed.2011.616