Spatial analysis of the effects of PM2.5 on hypertension among the middle-aged and elderly people in China

Hypertension is currently one of the most common chronic diseases with high global prevalence associated with a huge social and economic burden. In recent years, air pollution has become a focus of research, especially the effects of PM2.5 on hypertension. However, few studies have considered the spatial properties of the sample; thus, the results might be unreliable. Based on the China Health and Retirement Longitudinal Study (CHARLS) and the Environmental Status Bulletin for each province in China, we used the extended shared component model (SCM) to fit the spatial variation of hypertension risk and to reveal the impact of PM2.5 on hypertension in males and females. Our results revealed that the crude prevalence of hypertension for the whole population in China was 32.74% in 2015, with the prevalence in men experiencing slightly higher than that in women (32.92% vs. 32.58%). We found that the distribution of hypertension prevalence exhibited obvious spatial aggregation for the whole population in China (Moran's I = 0.39, P = 0.001), with similar results in both men (Moran's I = 0.18, P = 0.027) and women (Moran's I = 0.52, P = 0.001). Furthermore, the smoothed results obtained using the SCM indicated that some eastern and central provinces had relatively higher hypertension risk, while the risk in southeastern provinces was much lower. The risk was also relatively lower in most western provinces, except for some northwestern regions. Notably, our results showed that PM2.5 was a risk factor for hypertension, and the impact of PM2.5 on women was slightly greater than that on men, with odds ratios (OR) of 1.063 (1.041, 1.086) and 1.048 (1.025, 1.071), respectively. Our findings suggest the existence of distinct spatial differences in the prevalence of hypertension and small sex-related differences in the risk of hypertension in China.