Association of School Residential PM with Childhood High Blood Pressure: Results from an Observational Study in 6 Cities in China.

Objective: To investigate the association of long-term PM exposure with blood pressure (BP) outcomes in children aged 6-18 years, and to examine the population attributable risk (PAR) of PM exposure.

Methods: A total of 53,289 participants aged 6-18 years with full record of age, sex, BP, height, and local PM exposure from a cross-sectional survey conducted in 6 cities of China in 2013 were involved in the present study. PM data from 18 January 2013 to 31 December 2013 were obtained from the nearest environmental monitoring station for each selected school. Two-level linear and logistic regression models were used to evaluate the influence of PM on children's BP, and PAR was calculated in each sex and age group.

Results: Participants had a mean age of 10.8 (standard deviation: 3.4) years at enrollment, 51.7% of them were boys. U-shaped trends along with increased PM concentration were found for both systolic blood pressure (SBP) and diastolic blood pressure (DBP), with the thresholds of 57.8 and 65.0 μg/m, respectively. Both increased annual mean of PM concentration and ratio of polluted days were associated with increased BP levels and high blood pressure (HBP), with effect estimates for BP ranging from 2.80 (95% CI: -0.51, 6.11) mmHg to 5.78 (95% CI: 2.32, 9.25) mmHg for SBP and from 0.77 (95% CI: -1.98, 3.52) mmHg to 2.66 (-0.35, 5.66) mmHg for DBP, and the odds ratios for HBP from 1.21 (0.43, 3.38) to 1.92 (0.65, 5.67) in the highest vs. the lowest quartiles. Overall, 1.16% of HBP in our participants could be attributed to increased annual mean of PM concentration, while 2.82% could be attributed to increased ratio of polluted days. These proportions increased with age.

Conclusions: The association between long-term PM exposure and BP values appeared to be U-shaped in Chinese children aged 6-18 years, and increased PM exposure was associated with higher risk of HBP.