Effects of step count on BP may be mediated by obesity
More daily steps, as measured by the Apple Watch, were associated with lower home BP, but the association became nonsignificant after adjustment for BMI.
According to findings presented at the American College of Cardiology Scientific Session, when adjusted for age, sex, family structure and Apple Watch wear time, for every 1,000-step increase, participants experienced a change in systolic BP of –0.45 mm Hg (P = .015) and diastolic BP of –0.36 mm Hg (P = .006).
In contrast, when researchers included BMI in these adjustments, the observed changes in systolic and diastolic BP became nonsignificant (change in systolic BP, 0.09 mm Hg; P = .58; change in diastolic BP, 0.01 mm Hg; P = .95).
According to the presentation, average daily step count was 7,531 and average home systolic BP was 122 mm Hg and diastolic BP was 76 mm Hg.
“In this sample of community-based participants who are primarily middle-aged, higher physical activity was associated with lower home blood pressure. In our exploration model, it appeared that majority of this association is mediated or accounted for by the body mass index,” Mayank Sardana, MD, clinical fellow at the University of California, San Francisco, said during a consumer web briefing. “I want to stress that this analysis does not establish causality or directionality of association in any way. We cannot say that lower step count led to higher blood pressure based on this study because we know from prior literature that the lower step count as reported by self-report or the use of accelerometer was associated with lower risk of hypertension.”
In the fully adjusted model accounting for BMI, the effect of step count on BP was not significant in men (systolic BP, –0.17 mm Hg; P = .52; diastolic BP, –0.02 mm Hg; P = .91) and women (systolic BP, 0.21 mm Hg; P = .33; diastolic BP, –0.002 mm Hg; P = .99).
Participants were from the electronic Framingham Heart Study (n = 638; mean age, 55 years; 59% women; 10% nonwhite; 29% with hypertension) and wore an Apple Watch daily that transmitted weekly home BP readings (Nokia Withings cuff). Participants wore the watch at least 5 hours per day for at least 30 days and transmitted three or more BP readings during a median follow-up of 280 days.
“This study solidifies our understanding of the relationship between physical activity and blood pressure and raises the possibility that obesity or body mass index accounts for a lot of that relationship,” Sardana said in a press release. “Going forward, it would be useful to look at how smart devices might be leveraged to promote physical activity, reduce the burden of obesity and potentially reduce blood pressure.” – by Scott Buzby
Sardana M, et al. Abstract 1361-129. Presented at: American College of Cardiology Scientific Session; March 28-30, 2020 (virtual meeting).
Disclosure: Sardana reports no relevant financial disclosures.