Psychosocial Stress Modifies the Acute Cardiac Health Effects of Traffic-Related Air Pollution.

Previous studies have shown that exposure to black carbon (BC, a tracer of traffic-related air pollution) and psychosocial stress are both associated with adverse cardiac effects, but whether psychosocial stress could modify the cardiac effects of BC is unclear. To investigate the potential modifying effect of psychosocial stress on the associations between acute exposure to BC and typical cardiac health variables, real-time personal 24 h measurements were conducted in a repeated-measure study among adults with elevated blood pressure (high-risk group) and a panel study among normal adults (low-risk group) in China. Measured cardiac health variables included ST-segment depression events, heart rate, and heart rate variability (HRV) variables. Perceived Stress Scale, State Anxiety Inventory and Self-rating Depression Scale were used to assess the recent psychosocial stress status of the participants, and a composite stress index was established based on these scales. Generalized linear mixed-effects model was used to analyze the associations between BC exposure and cardiac health variables and potential effect modification by psychosocial stress. A total of 97 24 h measurements among 97 participants in the repeated-measure study and 202 24 h measurements among 87 participants in the panel study were included in the final analysis. Acute BC exposure was significantly associated with increased ST-segment depression events and heart rate and decreases in HRV in both studies. The marginal effects of acute BC exposure on most cardiac health variables generally tended to be amplified under higher vs low levels of psychosocial stress in both studies, with the composite stress index apparently modifying the associations of BC exposure with most ST-segment depression events and HRV variables. These findings suggest that psychosocial stress may increase the participants' cardiac susceptibility to BC exposure, which could be helpful for the identification of susceptible individuals in the context of traffic-related air pollution.