The Rotterdam cohort study of 13,115 subjects, studied for up to 22 years, included 1,566 patients with COPD, who had a 20% higher incidence of stroke during the study, particularly following an exacerbation of COPD. However this association was no longer significant after adjusting for smoking, which indicates that smoking is a common risk factor for both conditions. The risk may have been higher, but COPD patients appear to be dying due to cardiovascular disease first, or early attention to cardiovascular disease attenuates the risk of stroke (Portegies 2016).