Attributable risk fraction of prehypertension on cardiovascular disease mortality in the Japanese population: The Ohsaki study

Background: Although relative risk of prehypertension (pre-HT) on cardiovascular disease (CVD) mortality is modest, prevalence of pre-HT is large, that is, population attributable fraction (PAF) of pre-HT on CVD mortality might be large. However, no studies have reported the fraction. Methods: We followed 12,928 Japanese National Health Insurance (NHI) beneficiaries aged 40-79 years without a history of CVD. On the basis of their blood pressure (BP), the participants were categorized as normal BP, pre-HT, and hypertension (HT) (Seventh Report of the Joint National Committee criteria). Multivariate-adjusted Cox proportional hazards model was used to estimate the hazard ratio (HR) of the BP status vs. CVD mortality. Results: During 12-years of follow-up, 321 participants died of CVD. As positive relation between BP category and CVD mortality was steeper in middle-aged (40-64 years) than that in elderly (65-79 years), we separately calculated PAF on CVD mortality among middle-aged and elderly. HR (95% confidence interval) for cardiovascular mortality for pre-HT and HT, respectively, was 1.31 (0.59-2.94) and 2.98 (1.39-6.41) in middle-aged, and 1.03 (0.62-1.70) and 1.65 (1.02-2.64) in elderly. Non-normal BP, i.e., pre-HT and HT, accounted for 47 and 26% of the CVD deaths among the middle-aged and elderly participants, respectively. Although the PAF of pre-HT was larger in the middle-aged participants (7%) than that in the elderly ones (0%), neither fraction was considered large. Conclusion: The PAF on CVD mortality in pre-HT was not large compared with that in HT.