Age-specific effects of systolic and diastolic blood pressures on mortality due to cardiovascular diseases among Japanese men (NIPPON DATA80*)

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Abstract
Objective To clarify the relationship between mortality due to cardiovascular diseases (CVD) and systolic blood pressure (SBP) and diastolic blood pressure (DBP) in young and elderly Japanese men in the absence of antihypertensive treatments. Design A 19-year cohort study using the 1980 National Survey of Cardiovascular Diseases and the identification of the underlying causes of death using national vital statistics data. Methods In 1999, a 19-year follow-up study was conducted among participants randomly selected from the Japanese population for the 1980 National Survey of Cardiovascular Diseases. Among the male participants that were not receiving antihypertensive treatment, information was obtained for about 91.3% of the subjects (n = 3779). Age-adjusted mortality rates using the person-year method were calculated to compare the relationships of SBP and DBP levels with CVD mortality for different age groups (aged 30–64, 65–74, and 75 years or more). Results The total number of observed person-years was 64 598 and the number of CVD-related deaths after 19 years was 253. Both SBP and DBP levels were significantly and linearly related to CVD mortality in the age groups 30–64 years (P < 0.001 and P = 0.01, respectively) and 65–74 years (P < 0.001 and P = 0.03, respectively). In the group of participants that were at least 75 years old, however, no significant increase in the relative risk of CVD was observed with increasing DBP levels (P = 0.156), whereas the relative risk of CVD increased significantly with increasing SBP levels (P = 0.038). Multivariate analysis adjusting for major risk factors confirmed these relationships. Standardized hazard ratios (95% confidence intervals) of SBP were 1.53 (1.19–1.96) for 30–64 year olds, 1.70 (1.31–2.20) for 64–74 year olds, and 1.23 (1.03–1.47) for participants 75 years old or more, whereas those of DBP were 1.52 (1.12–2.06), 1.60 (1.21–2.10), and 1.10 (0.94–1.28), respectively. Conclusions These data show that elevated SBP is an independent risk factor for CVD mortality for Japanese men of all ages, whereas elevated DBP is not an independent risk factor for CVD mortality for elderly men.