Background: The effect of very high or extremely high levels of high-density lipoprotein cholesterol (HDL-C) on cardiovascular disease (CVD) is not well described. Although a few recent studies have reported the adverse effects of extremely high levels of HDL-C on CVD events, these did not show a statistically significant association between extremely high levels of HDL-C and cause-specific CVD mortality. In addition, Asian populations have not been studied. Objective: We examine the impact of extremely high levels of HDL-C on cause-specific CVD mortality using pooled data of Japanese cohort studies. Methods: We performed a large-scale pooled analysis of 9 Japanese cohorts including 43,407 participants aged 40–89 years, dividing the participants into 5 groups by HDL-C levels, including extremely high levels of HDL-C ≥2.33 mmol/L (≥90 mg/dL). We estimated the adjusted hazard ratio of each HDL-C category for all-cause death and cause-specific deaths compared with HDL-C 1.04–1.55 mmol/L (40–59 mg/dL) using a cohort-stratified Cox proportional hazards model. Results: During a 12.1-year follow-up, 4995 all-cause deaths and 1280 deaths due to overall CVD were identified. Extremely high levels of HDL-C were significantly associated with increased risk of atherosclerotic CVD mortality (hazard ratio = 2.37, 95% confidence interval: 1.37–4.09 for total) and increased risk for coronary heart disease and ischemic stroke. In addition, the risk for extremely high HDL-C was more evident among current drinkers. Conclusion: We showed extremely high levels of HDL-C had an adverse effect on atherosclerotic CVD mortality in a pooled analysis of Japanese cohorts.
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