Association Between White Blood Cell Count and Atrial Fibrillation Risk ― A Population-Based Prospective Cohort Study -

Background: The incidence and prevalence of atrial fibrillation (AF) are increasing. The white blood cell (WBC) count is an indicator of systemic inflammation and is related to increased cardiovascular disease risk. Using data from the Suita Study, we investigated the association between WBC count and AF risk in the general Japanese population. Methods and Results: This prospective cohort study included 6,884 people, aged 30–84 years, with no baseline AF. Cox regression was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for AF incidence by WBC count quintile. Within a median follow-up period of 14.6 years, 312 AF cases were diagnosed. Compared with the lowest WBC count quintile, the highest quintile was associated with an increased AF risk (HR 1.57; 95% CI 1.07–2.29). The association was more pronounced among women than men (HR 2.16 [95% CI 1.10–4.26] and 1.55 [95% CI 0.99–2.44], respectively; P interaction=0.07), and among current than non-smokers (HR 4.66 [95% CI 1.89–11.50] and 1.61 [95% CI 1.01–2.57], respectively; P interaction=0.20). For each 1.0×109-cells/L increment in WBC count, AF risk increased by 9% in men (9% in non-smokers, 10% in current smokers) and 20% in women (13% in non-smokers, 32% in current smokers). Conclusions: A higher WBC count was positively associated with an elevated AF risk in the general Japanese population, especially in women who smoked.