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(Stroke. 2009;40:1571.)
© 2009 American Heart Association, Inc.

Original Contributions

Trends for Blood Pressure and Its Contribution to Stroke Incidence in the Middle-Aged Japanese Population

The Circulatory Risk in Communities Study (CIRCS)

Hironori Imano, MD; Akihiko Kitamura, MD; Shinichi Sato, MD; Masahiko Kiyama, MD; Tetsuya Ohira, MD; Kazumasa Yamagishi, MD; Hiroyuki Noda, MD; Takeshi Tanigawa, MD; Hiroyasu Iso, MD Takashi Shimamoto, MD

From Osaka Medical Center for Health Science and Promotion (H.I., A.K., S.S., M.K., T.S.), Osaka, Japan; Public Health (T.O., H.I.), Department of Social and Environmental Medicine, Graduate School of Medicine, Osaka University, Osaka, Japan; Department of Public Health Medicine (K.Y.), Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan; Harvard Center for Population and Development Studies (H.N.), Harvard School of Public Health, Cambridge, Mass; Department of Environmental Health and Social Medicine (T.T.), Ehime University School of Medicine, Matsuyama, Japan.

Correspondence to Hironori Imano, MD, Public Health, Department of Social and Environmental Medicine, Osaka University Graduate School of Medicine, 2–2 Yamadaoka, Suita, Osaka 565-0871, Japan. E-mail imano{at}kenkoukagaku.jp

Background and Purpose— Hypertension is a major risk factor for stroke. However, a substantial decrease in blood pressure levels in Japanese during the past 3 decades may have reduced contributions of hypertension to risk of stroke. The population attributable fraction, the percentage of outcomes attributable to exposure, of blood pressure for the incidence of stroke was investigated during 3 survey periods between 1963 and 1994 by means of a population-based cohort study.

Methods— We explored 3 cohort data of residents aged 40 to 69 years in 4 Japanese communities in 1963 to 1971 (n=5439), 1975 to 1984 (n=9945), and 1985 to 1994 (n=11 788) baseline surveys. Mean follow-up period for each cohort was 10 years.

Results— Higher blood pressure levels were associated with higher risk of stroke. Positive associations were also observed even within nonhypertension levels. From the first to the third cohorts, the blood pressure category with a majority of stroke incidence shifted from severe or moderate hypertension to mild hypertension. The population attributable fraction of the severe hypertension category in the first, second, and third cohorts were 20%, 14%, and 9%, respectively, and those of the moderate hypertension category were 19%, 24%, and 11%, respectively, whereas those of the mild hypertension category were 17%, 26%, and 23%, respectively. The results were similar when participants on antihypertensive medication were excluded.

Conclusions— The higher risk of stroke incidence with higher blood pressure levels even in nonhypertension categories and the shift of stroke burden from severe/moderate hypertension to mild hypertension support the early management of hypertension and primary prevention of high blood pressures for the prevention of stroke.

Key Words: blood pressure • population attributable fraction • stroke • incidence • follow-up study

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