Introduction

High blood pressure (BP), known as hypertension, is a critical global health challenge because of its high prevalence and its role in the development of cardiovascular disease. Hypertension has been identified as the leading preventable risk factor for premature mortality and is ranked first as a cause of disability-adjusted life-years [1]. Randomized clinical trials have also demonstrated that antihypertensive treatment substantially reduces cardiovascular disease risk [2].

Current estimates of the global burden of hypertension and of the treatment and control of hypertension help us to understand these public health concerns. National health surveys have indicated that the prevalence, awareness, treatment, and control of hypertension have all substantially improved in recent decades, especially in high-income countries with well-functioning health systems, such as Japan, the USA, and the European countries [3, 4]. Understanding of how these countries, with different lifestyle, health systems, and clinical guidelines, compare in terms of awareness, treatment, and control of hypertension can inform improvements and bring more effective and efficient prevention and management of hypertension.

This review of serial national surveys presents the trends in the prevalence, treatment, and control of hypertension in Japan and compares these with similar trends in the USA and European countries, providing insights into the reasons for the differences.

Prevalence, treatment, and control of hypertension in Japan

In Japan, levels of systolic BP steadily decreased during the years 1961–2016, by ≈10–20 mmHg in all age groups of men and women (Fig. 1) [5, 6]. The population-wide decline in systolic BP may be attributed to the screening and early identification of high BP or hypertension, lifestyle changes (including reduced salt intake), and improved hypertension treatment. Over the same period, the levels of diastolic BP also decreased, by ≈4–8 mmHg among all age groups of women but not among men aged 30–59 years (Fig. 2) [5, 6]. The recalcitrant diastolic BP trend in men aged 30–59 years may be explained by an increase in obesity, decrease in physical activity, and insufficient treatment of diastolic hypertension in this group [5,6,7].

Fig. 1: Trends in mean systolic blood pressure across age groups by sex from 1961 to 2016 in Japan.
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Reprint from Hypertension Research (Hisamatsu et al. [6]) with permission, copyright © 2020, Springer Nature.

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Fig. 2: Trends in mean diastolic blood pressure across age groups by sex from 1961 to 2016 in Japan.
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Reprint from Hypertension Research (Hisamatsu et al. [6]) with permission, copyright © 2020, Springer Nature.

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The prevalence of hypertension, defined as BP ≥ 140/90 mmHg or use of antihypertensive medication, during the years 1980–2016 is presented in Fig. 3 [5, 6]. Over those 36 years, the prevalence decreased in women of all ages and in younger men aged 30–49 years. In contrast, this trend was not evident in men aged ≥50 years—in men aged 50–69 years, the prevalence of hypertension increased after 2000. In recent years, the prevalence of hypertension has remained high and has been found in over 60% of men aged ≥50 years and women aged ≥60 years. These trends suggest that the strong decline in BP levels until 2016—particularly in middle-aged and older groups of Japanese men and women, as shown in Fig. 1, can be mainly attributed to the development and expansion of medical treatment for hypertension that occurred during that time [6].

Fig. 3: Trends in the prevalence of hypertension across age groups by sex from 1980 to 2016 in Japan. Hypertension was defined as blood pressure ≥140/90 mmHg or the use of antihypertensive medication.
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Reprint from Hypertension Research (Hisamatsu et al [6]) with permission, copyright © 2020, Springer Nature.

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The hypertension treatment rate, defined as the proportion of hypertensive patients receiving antihypertensive medication, increased during the years 1980–2016 (Fig. 4) [5, 6], with no differences between the sexes. In 2016, in both sexes, >50% of hypertensive patients aged 60–69 years and >60% of those aged 70–79 years took antihypertensive medication.

Fig. 4: Trends in the treatment rate of hypertension across age groups by sex from 1980 to 2016 in Japan. The treatment rate was calculated as the proportion of use of antihypertensive medication among patients with hypertension.
figure 4

Reprint from Hypertension Research (Hisamatsu et al. [6]) with permission, copyright © 2020, Springer Nature.

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The trend in the hypertension control rate, defined as the proportion of treated hypertensive patients achieving BP < 140/90 mmHg, during the years 1980–2016 is presented in Fig. 5 [5, 6]. The hypertension control rate increased over the 36-year span, improving to ≈40% in both men and women by 2016. There was no difference in hypertension control among the age groups.

Fig. 5: Trends in the control rate of hypertension across age groups by sex from 1980 to 2016 in Japan. The control rate of hypertension was defined as the proportion of those with BP < 140/90 mmHg among hypertensive patients taking antihypertensive medication.
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Reprint from Hypertension Research (Hisamatsu et al. [6]) with permission, copyright © 2020, Springer Nature.

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It has been estimated that there were 43 million hypertensive individuals in Japan in 2017, of whom 31 million (73%) had poor control [6, 8]. Among those with poor control, 14 million (33%) were unaware of their hypertension and 4.5 million (11%) were aware of their condition but were not receiving treatment, while 12.5 million (29%) were aware and were receiving treatment but with poor control. Among all estimated hypertensive individuals, only 12 million (27%) were estimated to have maintained their BP below 140/90 mmHg.

These findings indicate that hypertension is a nationwide concern and suggest that, particularly in men, it is necessary to monitor BP regularly (e.g., with home BP measurement), to strive to maintain a “normal BP” from young adulthood, and to initiate lifestyle modification early to prevent hypertension later in life.

Comparison with the USA and European countries

The data on prevalence, treatment, and control of hypertension depend upon the definition of hypertension, the criteria for treatment, and the targeted BP (as determined by patient risk factors). The 2017 joint American College of Cardiology/American Heart Association guidelines on BP management newly defined hypertension as BP ≥ 130/80 mmHg, impacting both the eligibility for treatment and the criterion for control in the USA [9]. In contrast, the 2019 Japanese Society of Hypertension (JSH) Guidelines for the Management of Hypertension [8] and the 2018 European Guidelines for the Management of Arterial Hypertension [10] both retained the existing hypertension definition of BP ≥ 140/90 mmHg. Based on the definition of hypertension as BP ≥ 140/90 mmHg, the pooled data suggest that in 2000, ≈26% of the world’s adult population had hypertension [11]. In 2010, this estimate increased to ≈31% or roughly, 1.4 billion adults with hypertension [12].

Based on the latest national survey data from 12 high-income countries and a definition of hypertension as BP ≥ 140/90 mmHg or treatment with antihypertensive medication, the prevalence of hypertension in Japan was similar to or higher than that in the USA and most European countries in the years around 2015 (Fig. 6) [3]. For example, in Japan, the USA, and UK, respectively, the hypertension prevalence was 40%, 44%, and 36% in women and was 56%, 45%, and 40% in men. Notably, Japanese men had the second highest prevalence of hypertension among the high-income countries (Finland had the highest prevalence, while Canada and the UK had the lowest). Similarly, BP levels and hypertension prevalence were found to be higher in Japan compared with the USA in regional community-based studies of the two countries after 2000 [13]. Nevertheless, that hypertension prevalence remained at ≈40–60% around 2015 among high-income countries indicates there has been little progress in the prevention and management of hypertension in those countries despite their well-functioning health systems.

Fig. 6: Prevalence of hypertension and rates of awareness, treatment, and control in women aged 40–79 years in 12 high-income countries.
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Results shown are crude (i.e., not age-standardized) to reflect the total burden of hypertension and its awareness, treatment, and control. The prevalence of hypertension was defined as blood pressure ≥140/90 mmHg or the use of antihypertensive medication. Among participants with hypertension, the proportion of those who were aware of their condition (awareness), were treated (treatment), and whose hypertension was controlled (i.e., <140/90 mmHg) (control) were calculated. *The latest national survey in Ireland had data for people aged 50–79 years; data from an earlier survey in 2007 were used for people aged 40–49 years. †The question on awareness was not asked in 2015 in Japan; awareness data from 2010 were used. ‡The latest national survey in Spain had data for people aged 60–79 years; data from an earlier survey in 2009 were used for people aged 40–59 years. Modified from The Lancet (NCD Risk Factor Collaboration [3]), copyright © 2020, Elsevier.

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Factors contributing to differences in prevalence

The difference in hypertension prevalence may be attributed to differences in lifestyle between Japan and the Western (USA and European) countries. Hypertension is a complex condition resulting from the interaction of multiple environmental and genetic factors (the rare occurrence of hypertension or age-related increases in systolic and mean BP in nonindustrialized societies confirms the important role of environmental exposure in defining hypertension risk) [14, 15]. High sodium intake has been linked to excess fluid intake, decreased arterial compliance, impaired renin–angiotensin activity, and reduced glomerular filtration rate, all of which exacerbate the hypertensive burden [16]. Dietary potassium promotes natriuresis and vasodilation [17], thereby lowering BP, and this suggests that low potassium intake also influences developing hypertension. The INTERMAP study in the 1990s showed that mean dietary intake of sodium measured by 24-h urine collection was higher in the Japanese than in the US and UK populations (urinary sodium was, respectively, 4278 mg/day, 3272 mg/day, and 2929 mg/day for women and 4843 mg/day, 4202 mg/day, and 3702 mg/day for men), while the opposite was true for potassium intake (urinary potassium was, respectively, 1891 mg/day, 1982 mg/day, and 2378 mg/day for women and was 1920 mg/day, 2512 mg/day, and 2912 mg/day for men); thus, the sodium–potassium ratio was higher in the Japanese than in the Western samples [18]. The differences in sodium intake between Japan and the Western countries endured in the 2010 s [19].

In general, Japanese men have a higher alcohol consumption than do Western men; [18] at the same time, almost half of Japanese have an atypical allele of the aldehyde dehydrogenase 2 gene, which has lesser capacity to catalyze acetaldehyde metabolism, producing an elevated BP after drinking [20]. Further, for the past 40 years, cigarette smoking has been more prevalent among Japanese men than among Western men [21], and given the effect of smoking on arterial stiffness and wave reflection, this too may have great detrimental effect on BP in Japanese men [22]. Notably, a lower prevalence of obesity [23] and a higher level of physical activity have historically been reported in Japan than in Western countries [24], although recently, both an increase in obesity and decease in physical activity have been observed with the increasingly “Westernized” Japanese lifestyle, especially in men, likely contributing to a higher burden of hypertension [6, 7].

Factors contributing to difference in awareness, treatment, and control

An analysis of national surveys from 12 high-income countries investigated levels of hypertension awareness, treatment, and control (according to the definition of BP < 140/90 mmHg) among individuals with hypertension (BP ≥ 140/90 mmHg or treated with antihypertensive medication) and found that in most countries, all of these have improved over the past 30 years, especially during the 1990s and early 2000s; [3] however, Japan ranked among the countries with the lowest levels (for all), while the USA ranked among the highest, in the years around 2015 (Figs. 6 and 7). For example, the rates of hypertension awareness, treatment, and control were observed, respectively, in 66%, 55%, and 29% of women and in 65%, 52%, and 24% of men in Japan, compared with 86%, 80%, and 54% of women and 79%, 70%, and 49% of men in the USA. A limitation of this review is that the thresholds for the diagnosis of hypertension and target BP level for the treatment of hypertension were both defined as 140/90 mmHg and thus they were not necessarily based on the hypertension guidelines of each country at that time.

Fig. 7: Prevalence of hypertension and rates of awareness, treatment, and control in men aged 40–79 years in 12 high-income countries.
figure 7

Results shown are crude (i.e., not age-standardized) to reflect the total burden of hypertension and its awareness, treatment, and control. The prevalence of hypertension was defined as blood pressure ≥140/90 mmHg or the use of antihypertensive medication. Among participants with hypertension, the proportion of those who were aware of their condition (awareness), were treated (treatment), and whose hypertension was controlled (i.e., <140/90 mmHg) (control) were calculated. *The latest national survey in Ireland had data for people aged 50–79 years; data from an earlier survey in 2007 were used for people aged 40–49 years. †The question on awareness was not asked in 2015 in Japan; awareness data from 2010 were used. ‡The latest national survey in Spain had data for people aged 60–79 years; data from an earlier survey in 2009 were used for people aged 40–59 years. Modified from The Lancet (NCD Risk Factor Collaboration [3]), copyright © 2020, Elsevier.

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The increases in awareness, treatment, and control of hypertension seen in the high-income countries in recent decades are probably the result of a combination of factors: [3] first, the introduction of simplified clinical guidelines for hypertension has been met with increasing uptake and compliance. Second, the introduction of lower thresholds for diagnosis and initiation of treatment have also contributed to higher rates of awareness, treatment, and control. Third, over time, newer drugs (e.g., renin-angiotensin system inhibitors and calcium-channel blockers) have become available and improved treatment efficacy and control (with fewer side-effects) over that seen with older generation agents, such as the thiazide diuretics. Finally, nationally implemented screening and preventive health programs may also have contributed to the observed improvements. Nonetheless, the overall high prevalence of uncontrolled hypertension (>40% in women and >50% in men in most countries) remains a major risk factor for future cardiovascular disease even in countries with well-functioning healthcare systems.

It is thus surprising that improvements in hypertension awareness, treatment, and control have been relatively low in Japan compared with in the USA and European countries, since Japan has a well-developed universal health insurance and preventive health system. It may be that the relatively slow Japanese adoption of guidelines with lower thresholds for diagnosis and initiation of treatment has played a role in this [25]. As late as 1990 Japan used a BP of 160/95 mmHg as the criterion for hypertension diagnosis and only in 2000 lowered the threshold to 140/90 mmHg [26], while the USA adopted the more stringent treatment criterion of 140/90 mmHg in 1993 [27]. Furthermore, the clinical guidelines also differ in other ways between Japan and the Western countries, for example, regarding the recommendations for patients with BP between 140/90 mmHg and 160/100 mmHg and few risk factors [3]. For patients in this hypertensive category, the 2019 JSH guidelines recommend lifestyle changes before initiating treatment [8], while the 2017 American College of Cardiology/American Heart Association guidelines recommend immediate treatment [9]. As a result, physicians in Japan are less likely to proactively treat patients with BP between 140/90 mmHg and 160/100 mmHg than their counterparts in Western countries [28, 29]. In addition, physicians in Japan may be cautious about treating hypertension in older patients [4] who are generally more susceptible to adverse effects (e.g., hypotension, fall injury, and polypharmacy) from antihypertensive medication than are younger adults. In fact, the 2019 JSH guidelines propose the BP goal <140/90 mmHg for older patients aged ≥75 years and the BP goal <130/80 mmHg for those aged <75 years [8], whereas the 2017 American College of Cardiology/American Heart Association guidelines dictate that BP < 130/80 mmHg should be targeted after the age of 65 years [9]. The term “clinical inertia” describes the failure of some physicians to recognize the need to intensify the antihypertensive treatment approach according to the guidelines and is a great barrier to the achievement of BP control in patients with hypertension [8]. A fundamental change in the attitudes of Japanese physicians may be needed to achieve levels of hypertension treatment and control similar to those in the Western countries [4]. Continuing study of the factors underlying the observed outcome differences is warranted, to improve the awareness, treatment, and control of hypertension.

Future plans for managing hypertension in Japan

If the prevalence and treatment and control rates observed in 2017 persist, there will be an estimated 44 million hypertensive patients in Japan by 2028 and among them, 32 million hypertensive patients with poor control. In an effort to conquer hypertension, the JSH has outlined a plan [30] that aims to reduce the number of hypertensive individuals with BP ≥ 140/90 mmHg by 7 million over the next decade, thereby extending healthy life expectancy in Japan. The number of hypertensive individuals with poor control will decrease by the targeted 7 million—from 31 million in 2017 to 24 million in 2028—if the following are achieved: (1) the hypertension prevalence decreases by 5 percentage points (the number of hypertensive individuals decreases by 3.2 million); (2) the hypertension treatment rate increases by 10 percentage points (the number of hypertensive individuals decreases by 1.9 million); and (3) the hypertension control rate (defined as BP < 140/90 mmHg among hypertensive individuals taking antihypertensive medication) increases by 10 percentage points (the number of hypertensive individuals decreases by 2.8 million) [6].

Conclusion

That the prevalence of hypertension hovers at 40–60% in Japan as well as in the USA and in European countries suggests there has been little progress in the prevention of hypertension, even in high-income countries with well-functioning health systems. Clearly, even in such countries, the high (>40%) prevalence of uncontrolled hypertension remains an important risk factor for substantial morbidity and mortality. Compared with the USA and the European countries, improvements in awareness, treatment, and control of hypertension have been relatively low in Japan, and the underlying reasons for the differences between countries warrant further study. Health policy and research on prevention and early control of high BP, at the individual and public health levels, can reduce the prevalence and adverse sequelae of hypertension. Furthermore, proactive treatment and strict adherence to intensified antihypertensive treatment guidelines can more effectively bring BP to the targeted level. In addition, it is important to continue to carefully monitor and compare trends in hypertension across countries.