The purpose of this study was to examine the associations between daytime and nighttime ambulatory blood pressure (ABP) on carotid IMT when controlling for daytime physical activity (PA) in a sample of 201 healthy older adults (mean age 66.9 yrs, 49.8% females) who were part of the 6 year follow-up of the Pittsburgh Healthy Heart Project (PHHP). Daytime ABP and nighttime ABP were assessed every 45 minutes over a period of 3 days and 2 nights. Physical activity was measured by a wrist accelerometer, a waist accelerometer, and a self-report measure of physical activity. Regression analysis was used to analyze the association of daytime and nighttime ABP with carotid IMT and to determine the type of PA measure (wrist, waist, or self-report), and the time interval (1, 5, 10, 15 minutes prior to ABP) that has the greatest influence on daytime ABP. Results showed that PA 1 minute (wrist) and 10 minutes (waist) prior to ABP assessment accounted for 9% of the variance in daytime ABP. When entered separately into a regression model, both daytime SBP (F(1,194)=6.33, p=.01) and nighttime SBP (F(1,194)=6.46, p=.01) significantly predicted IMT. When entered simultaneously into the model, both daytime SBP(F(1,193)=1.81, p=.18) and nighttime SBP(F(1,193)=1.94, p=.17) lost their significance. However, after adjusting for PA, daytime SBP (F(1,193)=3.47, p=.06) was a marginally stronger predictor of IMT than nighttime SBP. This finding supports the specific prognostic importance of daytime ABP and, to that extent, may support work on a greater understanding of the daytime variables that uniquely influence daytime ABP as potential correlates of CVD risk
