Social support, social participation, and cardiovascular reactivity to stress in the Midlife in the United States (MIDUS) study

•High social support may facilitate lower cardiovascular responses to stress.•Diminished stress reactivity may predict lower motivated behaviour such as social participation.•We evaluated both hypotheses in a large, midlife sample.•High social support was associated with higher, rather than lower, reactivity in unadjusted analyses.•No robust associations between reactivity and social support or participation were observed. This study tested two hypotheses of associations between dimensions of social connectedness and cardiovascular reactivity to acute stress: (1) high social support predicts diminished cardiovascular responses to stress (i.e., the stress-buffering model of social support), and (2) diminished cardiovascular responses predict lower social participation, a form of motivated behaviour. Participants (N = 606) in the main Midlife in the United States study completed measures of social support and social participation and underwent psychophysiological stress testing. In unadjusted analyses, social support was positively, rather than inversely, associated with reactivity. Results withstood adjustment for several control variables, but not for depressive symptoms, which was associated with diminished reactivity. Further, diminished reactivity was associated with lower social participation, but not in fully adjusted models. No robust evidence was observed for either the stress-buffering model, or for an association between diminished reactivity and lower social participation. The implications for our understanding of links between social connectedness and cardiovascular reactivity are discussed.