Total daily physical activity and the risk of AD and cognitive decline in older adults

Abstract

Objective: Studies examining the link between objective measures of total daily physical activity and incident Alzheimer disease (AD) are lacking. We tested the hypothesis that an objective measure of total daily physical activity predicts incident AD and cognitive decline.

Methods: Total daily exercise and nonexercise physical activity was measured continuously for up to 10 days with actigraphy (Actical®; Philips Healthcare, Bend, OR) from 716 older individuals without dementia participating in the Rush Memory and Aging Project, a prospective, observational cohort study. All participants underwent structured annual clinical examination including a battery of 19 cognitive tests.

Results: During an average follow-up of about 4 years, 71 subjects developed clinical AD. In a Cox proportional hazards model adjusting for age, sex, and education, total daily physical activity was associated with incident AD (hazard ratio = 0.477; 95% confidence interval 0.273-0.832). The association remained after adjusting for self-report physical, social, and cognitive activities, as well as current level of motor function, depressive symptoms, chronic health conditions, and APOE allele status. In a linear mixed-effect model, the level of total daily physical activity was associated with the rate of global cognitive decline (estimate 0.033, SE 0.012, p = 0.007).

Conclusions: A higher level of total daily physical activity is associated with a reduced risk of AD.

Figure 1. Total daily physical activity over 10 consecutive days

A graphical summary of total daily physical activity from a single Memory and Aging participant. In this recording, the device recorded and averaged physical activity every 15 seconds for 10 complete days from 7 pm on November 3 through 7 pm on November 13. The time of day is displayed on the top of the figure (0.00 to 0.00). Activity can be seen to vary during the day, with low or absent activity usually noted between 23:00 and 7:00, when the participant was likely sleeping. The column on the right of the figure shows the total daily physical activity counts which were averaged to obtain mean total daily physical activity.

Figure 2. Total daily physical activity and risk of AD in old age

Expected risk of Alzheimer disease (AD) based on the entire cohort is illustrated for 2 hypothetical average participants with high (dotted line: 90th percentile, 4.90 × 10⁵ activity counts per day) and low levels (solid line: 10th percentile, 1.24 × 10⁵ activity counts per day) of total daily physical activity.