White blood cell count and risk of all-cause and cardiovascular mortality in nationwide sample of Japanese - Results from the NIPPON DATA90

Background: The association of white blood cell (WBC) count with all-cause and cardiovascular disease (CVD) mortality were examined in the National Integrated Project for Prospective Observation of Non-communicable Disease and Its Trends in the Aged (NIPPON DATA) 90. Methods and Results: A total of 6,756 Japanese residents (2,773 men and 3,983 women) throughout Japan without a history of CVD were followed for 9.6 years. A Cox proportional hazards regression model was used to estimate the relative risk (RR) and 95% confidence interval (CI). We documented 576 deaths with 161 deaths from CVD. Overall, after adjusting for several confounders including age, sex, body mass index at baseline, smoking status, alcohol consumption, regular exercise, diastlic blood pressure, total cholesterol, high-density lipoprotein-cholesterol and hemoglobin A1c, a graded association between WBC count and higher risk of allcause mortality was observed (WBC of 9,000-10,000 cells/mm³ vs WBC of 4,000-4,900: RR =1.61, 95% CI: 1.07-2.40, p for trend=0.02). Elevated WBC count was almost significantly associated with high risk of CVD mortality (WBC of 9,000-10,000 vs WBC of 4,000-4,900: RR=1.79, 95% CI: 0.97-3.71). These associations strengthened among women. Stratified by smoking status, never-smokers with WBC counts of 9,000-10,000 had a 3.2 fold elevated risk for CVD death compared with those with WBC counts of 4,000-4,900. Conclusions: The WBC count may have potential as a predictor for all-cause mortality, particularly CVD mortality.