Abstract MP059: Incremental Light Activity Associated with Greater Brain Volume in Individuals Not Meeting the Physical Activity Guidelines: Cross Sectional Observations from the Framingham Heart Study

Background: Recent evidence suggests that dementia appears linked to subclinical vascular changes, which may be attenuated by physical activity. The Physical Activity Guidelines for Americans (PA-Guidelines) are currently set at 150 min of moderate-to-vigorous physical activity (MVPA) per week, as a target for adults to achieve favorable health outcomes, but make no specific recommendations for prevention of dementia. Many Americans fall well below the PA-Guidelines. The aim of this investigation was to determine whether there is a continuum of lower intensities and volumes of physical activity associated with healthy brain aging even in individuals not meeting the PA-Guidelines. Methods: We included Framingham Heart Study (FHS) participants who wore an Actical accelerometer for ≥3 valid days (>10 h wear time per day) on their right hip during the most recent cohort examinations and completed brain magnetic resonance imaging (MRI) an average of 1.7 (±0.9) years later (n=2534): Offspring exam 9, Third Generation exam 2, and corresponding examinations of the Omni cohorts. Participants were excluded from this analysis if they had prevalent stroke or dementia (n=63) or met the 150 min MVPA per week PA-Guidelines (n=1158). Non-wear time (defined as 60 min of zero-counts, with two interruptions allowed) was removed. Sedentary time (<200 counts/min, <1.5 metabolic equivalents [METs]) and light activity (201-1485 counts/min, 1.5-3 METs) were only accumulated during 6 am-10 pm, were represented as proportions of wear time to account for differences in wear time among participants, and standardized to a 16 h day. MVPA (>1486 counts/min, ≥3 METs) and steps were accumulated at any time of day. The relations of physical activity measures to brain MRI measures were assessed using multivariable linear regression. Results: More than 53% of FHS participants did not meet the PA-Guidelines for MVPA during their last exam, and were thus included in this investigation (n=1313, 56 [±14] years old, 60% women). These participants took an average of 6149 [±3079] steps, spent 10.5 [±6.1] min MVPA, 13 h 36 min [±48 min] sedentary and 2 h 14 min [±48 min] in light activities per day. Each additional 40 min of light activity (spent in 1.5-3 METs) or 42 min less time spent sedentary was associated with 0.22% [±0.07%] greater total cerebral brain volume (TCBV), after adjusting for age, sex, body mass index, smoking, diabetes mellitus, and cardiovascular disease (p=0.001), equivalent to approximately 1.1 years less brain aging. Greater light activity and lower sedentary time were also associated with greater hippocampal volume (p<0.005). Conclusions: Our investigation demonstrates, in a community setting, that there may be a negative association of light physical activity with brain aging even among individuals not meeting the PA-Guidelines for MVPA.