ACE and susceptibility to pneumonia measurement: By using a case-crossover design, we were able to control for time-invariant between-person confounding factors, and our findings were consistent with those of previous studies, which showed no protective effect of ACE inhibitor use on pneumonia requiring hospitalization in a general population or among patients with coronary disease.13,14 A difference between ACE inhibitors and ARBs is that ACE inhibitors but not ARBs increase the level of substance P and improve symptomless dysphagia.28 We also investigated if the effects of ACE inhibitors and ARBs differed in a general population.