INS and endothelial dysfunction: Sun et al. (2009) found that exposing mice to ambient PM2.5 at the concentration of 72 μg/m3 for 6 hr each day over 10 weeks exacerbated insulin resistance by enhancing systemic inflammatory response and inflammation in adipose tissue. Other plausible mechanisms include autonomic nervous system imbalance and endothelial dysfunction that may be triggered by PM2.5, which would in turn induce vasoconstriction and result in reduced insulin sensitivity (Brook et al. 2008; Coogan et al. 2012).