The association between seven-day objectively measured habitual physical activity and 24h ambulatory blood pressure: the SABPA study
Few studies have examined objective physical activity in relation to 24 h ambulatory blood pressure (BP). We aimed to assess the association of 7-day objectively measured habitual physical activity with ambulatory BP in a sample of African and Caucasian school teachers (n = 216, age 49.7 years) from the sympathetic activity and blood pressure in Africans prospective cohort study. Hypertension (ambulatory systolic BP ≥ 130 and/or diastolic BP ≥ 80 mm Hg) was prevalent in 53.2% of the sample, particularly in black Africans. The hypertensive group spent significantly more awake time in sedentary activity (51.5% vs 40.8% of waking hours, P = 0.001), as well as doing less light- (34.1% vs 38.9%, P = 0.043) and moderate-intensity (14.0% vs 19.7%, P = 0.032) activities compared with normotensives, respectively. In covariate adjusted models, light-intensity activity time was associated with lower 24 h and daytime ambulatory systolic BP (β = -0.15, 95% confidence interval (CI): -0.26, -0.05, P = 0.004; β = -0.14, CI: -0.24, -0.03, P = 0.011) and diastolic BP (β = -0.14, CI: -0.25, -0.03, P = 0.015; β = -0.13, CI: -0.24, -0.01, P = 0.030), as well as resting systolic BP (β = -0.13, CI: -0.24, -0.01, P= 0.028). Sedentary time was associated only with 24 h systolic BP (β = 0.12; CI: 0.01, 0.22), which was largely driven by night-time recordings. Participants in the upper sedentary tertile were more likely to be ‘non-dippers’ (odds ratio = 2.11, 95% CI: 0.99, 4.46, P = 0.052) compared with the lowest sedentary tertile. There were no associations between moderate to vigorous activity and BP. In conclusion, objectively assessed daily light physical activity was associated with ambulatory BP in a mixed ethnic sample.