Air pollution, residential greenspace, and the risk of incident immune thrombocytopenic purpura: a prospective cohort study of 356,482 participants

This study investigated the associations of air pollution and residential greenspace with immune thrombocytopenic purpura (ITP) risk, along with their combined effects, in a cohort of 356,482 UK Biobank participants free of ITP at baseline. Ambient PM2.5, PMcoarse, PM10, NO2, and NOx exposures were estimated by land-use regression models and residential greenspace was calculated using land use data, defined as the percentage of outdoor greenspace surrounding each participant's home location. The hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated by using Cox proportional hazard models, and non-linear relationships were assessed using restricted cubic spline (RCS) curves. A total of 500 incident ITP cases were diagnosed during a median follow-up of 13.54 years. Long-term exposure to high ambient concentrations of PM2.5 (HR = 1.15, 95% CI: 1.04-1.28, P = 0.007), NO2 (HR = 1.23, 95% CI: 1.10-1.37, P = 1.83×10-4), and NOx (HR = 1.12, 95% CI: 1.03-1.21, P = 0.011), as well as low residential greenspace (HR = 0.77, 95% CI: 0.67-0.87, P = 7.96×10-5), were associated with an increased risk of ITP. RCS curve revealed a non-linear relationship of PM10 and NOx with ITP risk (P for non-linearity: 0.003 for PM10 and 0.030 for NOx). Participants with high air pollution and low residential greenspace had the highest risk of ITP, though no evidence of mediation or interaction effects were observed. In conclusion, long-term exposure to ambient PM2.5, PM10, NO2 and NOx may increase ITP risk, whereas residential greenspace may decrease this risk.