High Hematocrit Levels Are Associated with Risk of Cardiovascular Mortality among Middle-Aged Japanese Women: The Ibaraki Prefectural Health Study (IPHS)

High Hematocrit Levels Are Associated with Risk of Cardiovascular Mortality among Middle-Aged Japanese Women: The Ibaraki Prefectural Health Study (IPHS)

NOBUKO TAKAOKA,^1,2,3 TOSHIMI SAIRENCHI,^1,3,4 FUJIKO IRIE,⁵ MUNEHIRO MATSUSHITA,^1,6 MASANORI NAGAO,⁷ MITSUMASA UMESAWA,^3,8 YASUO HARUYAMA,¹ HIROSHI WATANABE,⁴ KAZUMASA YAMAGISHI,^3,4,9 HIROYASU ISO,¹⁰ GEN KOBASHI¹ and HITOSHI OTA^3,4

¹Department of Public Health, Dokkyo Medical University School of Medicine, Mibu, Tochigi, Japan
²Office of International Affairs, Center for International Cooperation, Dokkyo Medical University School of Medicine, Mibu, Tochigi, Japan
³Ibaraki Health Plaza, Mito, Ibaraki, Japan
⁴Ibaraki Health Service Association, Mito, Ibaraki, Japan
⁵Department of Health and Welfare, Ibaraki Prefectural Office, Mito, Ibaraki, Japan
⁶Department of Physical Recreation, Tokai University School of Physical Education, Hiratsuka, Kanagawa, Japan
⁷Office of Epidemiology, Radiation Medical Science Center for the Fukushima Health Management Survey, Fukushima Medical University, Fukushima, Fukushima, Japan
⁸Dokkyo Medical University, Mibu, Tochigi, Japan
⁹Department of Public Health Medicine, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
¹⁰Public Health, Department of Social Medicine, Osaka University Graduate School of Medicine, Suita, Osaka, Japan

In Japan, heart disease and cerebrovascular disease were the second and fourth leading cause of death, respectively in 2014. Hematocrit, the ratio of the red blood cells to the total volume of blood is known to play a role in cardiovascular diseases. However, the relationship between elevated hematocrit and the risk of cardiovascular disease based on sex has not been examined in Asian countries. We analyzed data from the Ibaraki Prefectural Health Study, a community-based large cohort study, which included 87,533 individuals, aged 40 to 79 years living in 38 municipalities of the Ibaraki Prefecture, who had completed an annual health checkup in 1993, and were followed until 2013. The hematocrit levels of the subjects were categorized into 5 quintiles (Q1-Q5), and hazard ratios for cause-specific mortality were calculated using the Cox proportional hazards regression models. Age and other cardiovascular risk factors were the covariates in the study. During the follow-up for a mean of 17.9 years, 1,207 deaths (615 men and 592 women) due to acute myocardial infarction (AMI) were reported in this population. The p values for the trend in the Q3-Q5 groups were 0.661 for men and 0.020 for women. Additionally, these values were significant in younger (40 to 59 years) women but not in older (60 to 79 years) women. This study is the first one to demonstrate an association between high hematocrit level and risk of AMI mortality in younger Japanese women, but not in men and older women.

Keywords —— acute myocardial infarction; cardiovascular diseases; cohort studies; hematocrit; Japanese women

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Tohoku J. Exp. Med., 2019, 249, 65-73

Correspondence: Nobuko Takaoka, Department of Public Health, Dokkyo Medical University School of Medicine, 880 Kita-kobayashi, Mibu, Tochigi 321-0293, Japan.

e-mail: takaoka@dokkyomed.ac.jp