Moderate-Intensity Physical Activity, Hippocampal Volume, and Memory in Older Adults With Mild Cognitive Impairment

Background. Greater physical activity (PA) is associated with better memory performance and greater hippocampal volume in older adults. However, most studies to date assessed PA via questionnaires and thereby lacked objective characterization of PA (eg, intensity, duration, etc.). Thus, we currently do not have a comprehensive understanding of PA characteristics that are important for neuroprotection, especially among older adults with mild cognitive impairment (MCI). Thus, using triaxial accelerometers, we examined the association between light-and moderate-intensity PA, total duration of PA, hippocampal volume, and memory in older adults with MCI. Methods. This cross-sectional study involved 310 older adults with MCI who completed neuropsychological tests of memory, and structural magnetic resonance imaging. Participants were instructed to wear the accelerometer on an elastic band on their hip at all times for 2 weeks. Average daily duration of light, moderate, and total PA (min/day) was calculated. Results. Moderate PA was associated with hippocampal volume (beta =.167, p =.003) after controlling for age, but light PA (beta = -. 021, p =.713) and total PA (beta =.011, p =.844) were not. Both light and moderate PAs were not associated with memory performance. Structural equation modeling demonstrated that moderate PA was not directly associated with memory but significantly contributed to hippocampal volume; hippocampal volume loss was significantly and directly associated with poor memory performance. Conclusions. Our results suggest that the benefits of moderate PA on memory among older adults with MCI are mediated by hippocampal volume. Furthermore, light PA may not reduce dementia risk among older adults with MCI.