A net social propagation index for blood pressure: evidence from a randomized trial

Abstract We report the first randomized trial evidence demonstrating that improvements in cardio-metabolic risk factors can spread through social networks in a manner analogous to infectious processes. Using the randomized design, we quantified a social reproductive number (R 0 )—the average number of additional individuals who experience cardiovascular health improvement as a result of exposure to one improving participant. For systolic blood pressure, the Social R₀ was 6 ( p < 0.01), indicating that health gains propagated well beyond directly treated individuals. In other words, the intervention’s effects spread with epidemic intensity (R 0 > 1). Importantly, the intervention substantially amplified this propagation dynamic. We observed population-averaged comparative R₀ ratios of 22.1–27.1 ( p < 0.01) for mean arterial pressure improvement, with similarly significant findings across additional endpoints. These results suggest that health improvements are not solely individual outcomes but can diffuse across social networks at scale—and that public health systems can intentionally enhance or dampen this diffusion by modifying the effective reproductive number of health behaviors.