Aging causes decline in brain health, which has a complex relationship with fitness and cognition. Here, we aimed to disentangle the interactions between these outcomes in healthy older adults. MRI was used to acquire anatomical and cerebrovascular reactivity (CVR) in all participants. VO2max and cognitive outcomes were also tested. Results revealed that increased CVR was associated with decreased fitness and cognitive performance, whereas increased grey matter volume was associated with increased fitness. It is apparent that the relationship between brain health and fitness and cognitive outcomes is intricate and other parameters, such as cerebral blood flow, are necessary to gain further understanding.