Low-intensity daily walking activity is associated with hippocampal volume in older adults

Abstract

Hippocampal atrophy is associated with memory impairment and dementia and serves as a key biomarker in the preclinical stages of Alzheimer's disease. Physical activity, one of the most promising behavioral interventions to prevent or delay cognitive decline, has been shown to be associated with hippocampal volume; specifically increased aerobic activity and fitness may have a positive effect on the size of the hippocampus. The majority of older adults, however, are sedentary and have difficulty initiating and maintaining exercise programs. A modestly more active lifestyle may nonetheless be beneficial. This study explored whether greater objectively measured daily walking activity was associated with larger hippocampal volume. We additionally explored whether greater low-intensity walking activity, which may be related to leisure-time physical, functional, and social activities, was associated with larger hippocampal volume independent of exercise and higher-intensity walking activity. Segmentation of hippocampal volumes was performed using Functional Magnetic Resonance Imaging of the Brain's Software Library (FSL), and daily walking activity was assessed using a step activity monitor on 92, nondemented, older adult participants. After controlling for age, education, body mass index, cardiovascular disease risk factors, and the Mini Mental State Exam, we found that a greater amount, duration, and frequency of total daily walking activity were each associated with larger hippocampal volume among older women, but not among men. These relationships were specific to hippocampal volume, compared with the thalamus, used as a control brain region, and remained significant for low-intensity walking activity, independent of moderate- to vigorous-intensity activity and self-reported exercise. This is the first study, to our knowledge, to explore the relationship between objectively measured daily walking activity and hippocampal volume in an older adult population. Findings suggest the importance of examining whether increasing nonexercise, lifestyle physical activities may produce measurable cognitive benefits and affect hippocampal volume through molecular pathways unique to those related to moderate-intensity exercise.

Keywords: African Americans; aging; brain; cognition; physical activity.

Figure 1. Distribution of walking activity by intensity

Moderate- to vigorous-intensity walking activity contributed to only 9.5% of total steps/day and 2.1% of total minutes of activity/day; Note. low-intensity activity: <100 steps/min; moderate- to vigorous-intensity activity: ≥ 100 steps/min

Figure 2. Relationship between daily walking activity and brain volume

A. Greater total daily walking activity was associated with larger hippocampal volume (adjusted for intracranial volume; ICV) in women. Associations remained significant for low-intensity daily walking activity, and after adding covariates exercise, moderate- to vigorous-intensity daily walking activity, age, years of education, body mass index (BMI), cardiovascular disease burden, and Mini Mental State Exam (MMSE). B. Total daily walking activity was not significantly associated with thalamus volume in women.