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Keywords:

  • hypertension;
  • characteristics;
  • Chinese;
  • dietary sodium;
  • blood pressure;
  • stroke

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

According to the 4th National Nutrition and Health Survey in 2002, the prevalence of hypertension in China was 18.8%. Despite that, the treatment rate among hypertensive patients was 82%, the control rate remained low in persons with hypertension (6%), because of the low awareness in general (30%) and the low control rate among treated hypertensive patients (25%). One of the major reasons for the increasing prevalence of hypertension is unbalance of dietary sodium and potassium intakes. In the International Study of Macro/Micro-nutrients and Blood Pressure (INTERMAP), Chinese, compared with American, British, and Japanese populations, had highest dietary sodium intakes and lowest potassium intakes, leading to a two to three times higher sodium/potassium ratio. High dietary sodium intakes may change the circadian rhythm of 24 h blood pressure, which is characterized by a higher night-time blood pressure. Indeed, the prevalence of isolated night-time hypertension, defined as a night-time blood pressure of at least 120 mmHg systolic or 70 mmHg diastolic and a daytime systolic/diastolic blood pressure less than 135/85 mmHg, was higher in Chinese than in Europeans. The complications of hypertension are also different across ethnicities, being mainly stroke instead of myocardial infarction in Chinese. Blood pressure lowering provides more protection against stroke than myocardial infarction, and calcium channel blockers provide more protection against stroke than other classes of antihypertensive drugs. Current Chinese hypertension guidelines recommend calcium channel blockers as the first of the five classes of antihypertensive drugs for stage 1 and low-risk hypertension.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

Hypertension is the most powerful cardiovascular risk factor, which may account for a large proportion of stroke and a substantial proportion of coronary heart disease and renal failure [1]. With the increasing longevity and obesity in most countries, the prevalence of hypertension is increasing rapidly, and hypertension is becoming a major public health burden. Despite the increasing number of efficacious antihypertensive drugs and increasing health insurance coverage in many countries, the control rate of hypertension remains low. Hypertension is apparently a complex disease closely related to lifestyle, which significantly differs across ethnicities. The pathophysiology of hypertension differs across populations, and might influence the management of hypertension and health outcomes. The present review describes several major characteristics of hypertension in the Chinese population.

High prevalence and low control rate

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

In the past 2 decades, two nationwide blood pressure surveys were conducted in China (Table 1) [2,3]. In 1991, about a million persons of at least 15 years were surveyed [2]. 11.3% had a blood pressure of at least 140 mmHg systolic or 90 mmHg diastolic or had used antihypertensive medication. The awareness, treatment and control rates were 26.6%, 12.1% and 2.8% respectively. Of those who were aware that they had hypertension, the treatment rate was 45.5%. Of those who were treated, the control rate was 23.1%. In the 4th National Health and Nutrition Survey in 2002, blood pressure was also measured [3]. In this survey of 141 892 subjects, the prevalence, treatment and control rates of hypertension increased to 18.8%, 24.7% and 6.1% respectively. The treatment rate in hypertensive patients increased to 81.8%. However, the awareness and the control rate in treated hypertensive patients remained virtually unaltered. In the elderly of at least 60 years, about half had hypertension, and the control rate was slightly higher than in younger subjects, mainly due to the higher awareness and treatment rate in hypertensive patients [3].

Table 1.   Prevalence, awareness, treatment and control rates of hypertension in two recent nationwide blood pressure surveys in China [2,3]
 Number of subjectsPrevalence (%)Awareness (%)Treatment (%)Aware and treated (%)Control (%)Treated and controlled (%)
1991 (≥15 years)950 35611.326.612.145.52.823.1
2002 (≥18 years)141 89218.830.224.781.86.125.0
2002 (≥60 years)Not reported49.137.636.296.37.624.1

If these two blood pressure surveys would be compared, several issues are noteworthy. The negative side was the 66% increase in the prevalence of hypertension from 1991 to 2002 [2,3]. The positive side was the almost twofold increase in the treatment rate and more than twofold increase in the control rate in hypertensive patients [2,3]. These changes in disease prevalence and management can well be explained by the societal changes. In the period from 1991 to 2002, China changed substantially in many aspects. The increase in the prevalence of hypertension could to some extent be attributable to the longevity of the Chinese population. Changes in the dietary pattern might also contribute. The increase in the treatment rate must have been driven by the increasing health insurance coverage in urban as well as rural areas. The reason for the unchanged low control rate in treated hypertensive patients might be complicated. Nonetheless, both the pathophysiology of the disease and the strategies of management might play a role.

High dietary intakes of sodium and low dietary intakes of potassium

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

It is well known that Chinese have high dietary intakes of sodium and low dietary intakes of potassium. In our recent population studies in Southern and Northern Chinese, urinary sodium excretion was 147.9 mmol/day [4] to 247 mmol/day in men [5] and 158.7 mmol/day [4] to 218 mmol/day in women [5]. The corresponding values were 25 mmol/day [4], 39 mmol/day [5], 27 mmol/day [4] and 39 mmol/day [5], respectively, for urinary potassium excretion, and 6.4 [4], 6.6 [5], 6.4 [4] and 6.1 [5], respectively, for urinary sodium/potassium ratio. If these values were compared with that of other populations, there is a difference in urinary sodium excretion, and a big difference in urinary potassium excretion and sodium/potassium ratio. Indeed, in the International Study of Macro/Micro-nutrients and Blood Pressure (INTERMAP) in American, British, Chinese and Japanese populations, the Chinese had the highest urinary sodium excretion and lowest urinary potassium excretion, and hence the highest urinary sodium/potassium ratio (Table 2) [6].

Table 2.   Urinary sodium and potassium excretions in four populations of the International Study of Macro/Micro-nutrients and Blood Pressure (INTERMAP) [6]
 JapanChinaUKUSA
Men N = 574 N = 516 N = 266 N = 1103
Urinary Na+ (mmol/day)211245161183
Urinary K+ (mmol/day)49.238.674.764.4
Urinary Na+/K+4.56.82.33.1
Women N = 571 N = 423 N = 235 N = 1092
Urinary Na+ (mmol/day)186210127142
Urinary K+ (mmol/day)48.537.961.050.8
Urinary Na+/K+4.16.02.23.1

In the Chinese population, there is apparently a need to decrease the dietary intakes of sodium. However, it is probably even more important to bridge the big gap for dietary potassium intakes. The extremely low potassium intake is a consequence of the typical Chinese dietary pattern, in which the main food is wheat or rice instead of potato and the meat is pork instead of beef. The latter food consists of much higher potassium than the former. The low dietary potassium intakes might at least in part explain why the Chinese hypertensive patients enrolled in the Hypertension in the Very Elderly Trial (HYVET) had a significantly lower serum potassium concentration than populations recruited from other countries (4.25 mmol/l versus 4.42 mmol/l in men and 4.26 mmol/l versus 4.38 mmol/l in women; < 0.05 for both sexes) [7].

The low dietary potassium intakes might be clinically important for the pathophysiology and management of hypertension in Chinese. Thiazide diuretics may increase urinary potassium excretion and in turn the risk of hypokalaemia even in American populations. Indeed, in the chlothalidone treatment group of the Systolic Hypertension in the Elderly Program, 166 (8.5%) patients had reported hypokalaemia [a serum potassium concentration below 3.5 mmol/l, < 0.001 versus 36 (1.9%) patients in the placebo group] at 3 years of follow-up, and 554 (23.4%) had started supplemental potassium treatment during the study [< 0.0001 versus 292 (12.3%) in the placebo group] [8]. In patients without diabetes mellitus at baseline, patients with significant thiazide-induced reductions in serum potassium concentration had an increased risk of new-onset diabetes [9]. Similar findings were observed in the chlothalidone group of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) [10]. Thus, in the Chinese population, thiazide diuretics might be efficacious in lowering blood pressure because of the high dietary sodium intakes, but might cause more hypokalaemia because of the low dietary potassium intakes.

High nocturnal level and low nocturnal fall in blood pressure

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

According to the pressure-natriuresis mechanism, an elevation in perfusion pressure in the renal artery would lead to a rapid increase in sodium and water excretion by the kidney [11]. When the dietary sodium intake is too high to be sufficiently excreted by the transiently elevated blood pressure, sustained high blood pressure develops. Because the normal circadian blood pressure rhythm follows a rule of nocturnal dipping from daytime, blood pressure elevation due to high dietary sodium intakes is therefore most likely to initiate in the sleep hours.

When we compared the ambulatory blood pressure monitoring data of our JingNing study with that of other population studies, we found that Chinese and Japanese had a significantly smaller nocturnal fall in systolic and diastolic blood pressure than Eastern and Western Europeans (Figure 1) [12]. We then further explored our data and found that a proportion of subjects (∼10%) had elevated blood pressure at night (≥120/70 mmHg) and normal blood pressure in the daytime (<135/85 mmHg). We did not see any apparent explanation for the elevated nocturnal blood pressure, such as, for instance, night-time shift and heavy alcohol drinking. We therefore defined this phenomenon as ‘isolated nocturnal hypertension’ according to the absolute blood pressure values in the daytime and at night as aforementioned [13,14]. In a 3.5-year follow-up study of these persons with ‘isolated nocturnal hypertension’, we found that ‘isolated nocturnal hypertension’ was reproducible in one-third of those who underwent a repeated ambulatory blood pressure recording [13]. In the International Database on Ambulatory blood pressure monitoring in relation to Cardiovascular Outcomes (IDACO), we found that ‘isolated nocturnal hypertension’ was associated with a twofold increase in total mortality and cardiovascular events, after adjustment for various risk factors including conventional blood pressure and daytime ambulatory blood pressure [15].

image

Figure 1.  Nocturnal fall in systolic and diastolic blood pressure in population studies [12]. Horizontal lines indicate the smallest systolic (full) and diastolic blood pressure (dashed) fall in the European populations. Mean values for systolic and diastolic fall at night are given above the bar for each of these studies. BPS, Belgian population study; EPOGH, European Project on Genes in Hypertension; AIB, Allied Irish Bank study; PAMELA, The Italian Pressioni Arteriose Monitorate e Loro Associazioni. Reproduced with permission from Wang JG, Li Y. Curr Hypertens Rep 2012; 14: 410–5

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In a scientific presentation on the international 24 h ambulatory blood pressure monitoring registry, Eastern Asians had higher night-time blood pressure than Europeans and South Americans. We recently studied the prevalence of ‘isolated nocturnal hypertension’ in treated hypertensive patients in our study of 24 h ambulatory blood pressure registry in Chinese outpatients, and found that approximately half treated hypertensive patients with controlled daytime blood pressure still had elevated blood pressure at night (Kang YY, et al. unpublished data).

High incidence of stroke and relatively low incidence of coronary heart disease

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

According to the annual statistics on the trends of stroke and coronary heart disease in the period from 1985 to 2005, the mortality rate of stroke remained four to five times higher than that of coronary heart disease, in spite of similar substantial increases in mortality of both diseases (Figure 2). Why stroke is more common than coronary artery disease in the Chinese population is not entirely understood. The low control rate of hypertension, the high dietary sodium intakes and the high nocturnal blood pressure may all contribute to the high incidence of stroke in the Chinese population.

image

Figure 2.  Trends in mortality of stroke and coronary heart disease from 1985 to 2005 according to China annual statistics of cardiovascular disease in 2005

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There is some evidence that the association between blood pressure and stroke is stronger in Eastern Asians than in other populations. In the Asia Pacific Cohort Studies Collaboration, after standardizing for age, a 10 mmHg higher systolic blood pressure was associated with 41% (95% confidence interval 40–42%) higher stroke risk in Asia and 30% (22–37%) higher stroke risk in Australia and New Zealand (< 0.003) [16]. The low control rate of hypertension in China would increase the incidence of stroke.

There is evidence that high dietary sodium intake is more closely associated with the risk of stroke than with the risk of coronary events. In the first National Health and Nutrition Examination Survey Epidemiologic Follow-up Study, dietary sodium intake, estimated at baseline using a single 24 h dietary recall method, was significantly associated with the risk of cardiovascular events and mortality in 2688 overweight but not in 6797 non-overweight persons [17]. In these overweight persons, the association with the specific cause of events was statistically significant only for stroke (for a 100 mmol/day higher sodium intake, hazard ratio 1.32, 95% confidence interval 1.07–1.64, = 0.01) but not for coronary heart disease (hazards ratio 1.06, 95% confidence interval 0.88–1.29, = 0.39). The high dietary sodium intake in China and other Eastern Asian countries might to some extent explain the high incidence of stroke in these populations.

There is also evidence that high night-time blood pressure is more closely associated with the risk of stroke than with the risk of coronary events. In IDACO, the fully adjusted hazards ratio associated with 10 mmHg high night-time systolic blood pressure was 1.23 (95% confidence interval 1.11–1.37) for stroke and 1.05 (0.93–1.18) for coronary events [18]. The high nocturnal blood pressure and the high prevalence of nocturnal hypertension would also increase the risk of stroke.

Use of calcium channel blockers

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

In China, the dihydropyridine calcium channel blocker is the most widely prescribed drug class in the management of hypertension. According to the Intercontinental Marketing Services (IMS) report in 2010, approximately 40% of treated hypertensive patients in China took a dihydropyridine calcium channel blocker. Calcium channel blocker is also the best evidenced drug class in China. Several placebo-controlled antihypertensive trials in China employed a dihydropyridine calcium channel blocker as the first-line drug of active antihypertensive treatment [19–22]. Indeed, nitrendipine was used in the Systolic Hypertension in China (Syst-China) trial [19,20], nifedipine in the Shanghai trial [21] and felodipine in the Felodipine Event Reduction (FEVER) trial [22]. Despite these calcium channel blockers being short- or intermediate-acting, active antihypertensive treatment significantly reduced the risk of fatal and nonfatal stroke, which is the major complication of hypertension in Chinese, by 38%, 58% and 27% in the Syst-China [19], Shanghai [21] and FEVER trials [22] respectively.

Several reasons might contribute to the common use of dihydropyridine calcium channel blockers in China. First, calcium channel blockers are more effective in Chinese in lowering blood pressure than other classes of antihypertensive drugs. Indeed, in a recent review of trials in Eastern Asians, mainly Chinese, calcium channel blockers reduced 24 h systolic/diastolic blood pressure more than other classes of antihypertensive drugs on average by 5/3 mmHg [23]. Second, calcium channel blockers, compared with other classes of antihypertensive drugs, provide more protection against stroke [24,25], and hence are more relevant in the prevention of cardiovascular complications, because the major complication of hypertension in Chinese is stroke, instead of myocardial infarction. In the recent Chinese FEVER trial, the incidence of stroke and coronary events was 15.9 and 6.2 per 1000 patient-years respectively [22]. Third, the dihydropyridine calcium channel blocker is particularly useful in the prevention and amelioration of coronary spasm that is more prevalent in Eastern Asians than in Europeans [26,27]. The incidence of coronary spasm after acetylcholine injection was 47% and 15% of arteries, respectively, in 15 Japanese and 19 Europeans within 14 days of an acute myocardial infarction (< 0.0001) [26].

Conclusions and perspectives

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

In China, the prevalence of hypertension is similar to that in other countries. However, the control rate of hypertension remains low in the past few decades. We might have to think about new strategies to improve treatment outcomes while accounting for the pathophysiology of hypertension in the Chinese population. Because hypertension is a complex disease, closely related to lifestyle, dietary intakes of sodium and potassium should be the most important factors for the pathophysiology, diagnosis and treatment of hypertension. We might have to measure night-time blood pressure, which is indeed higher in the Chinese than in other populations, and associated with an increased cardiovascular risk. We might also need different therapeutic strategies, particularly in the choice of first-line antihypertensive drugs. Calcium channel blockers are more efficacious in lowering blood pressure, in the prevention of stroke, which is the major complication of hypertension in Chinese and in avoiding metabolic side effects, for instance, hypokalaemia and new-onset diabetes.

More research is apparently required to improve our understanding in the pathophysiology and management of hypertension in Chinese. For instance, whether lowering uncontrolled night-time blood pressure would improve outcome will require randomized controlled trials. Probably only when these studies succeed, the goal of reducing cardiovascular events by lowering blood pressure can be achieved.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References

The authors were financially supported by grants from the National Natural Science Foundation of China (grants 30871360, 30871081 and 81170245), the Ministry of Science and Technology [2006BAI01A03 and a grant for China-European Union collaborations (1012)] and the Ministry of Education (NCET-09-0544), Beijing China, the Shanghai Commissions of Science and Technology (grant 07JC14047, the ‘Rising Star’ programme 06QA14043 and 11QH1402000) and Education (grant 07ZZ32 and the ‘Dawn’ project 08SG20), the Shanghai Bureau of Health (XBR2011004), Shanghai Jiaotong University School of Medicine (a grant of Distinguished Young Investigators to Yan Li) and the European Union (grants LSHM-CT-2006-037093 and HEALTH-F4-2007-201550).

References

  1. Top of page
  2. Summary
  3. Introduction
  4. High prevalence and low control rate
  5. High dietary intakes of sodium and low dietary intakes of potassium
  6. High nocturnal level and low nocturnal fall in blood pressure
  7. High incidence of stroke and relatively low incidence of coronary heart disease
  8. Use of calcium channel blockers
  9. Conclusions and perspectives
  10. Acknowledgements
  11. Conflicts of interest
  12. References
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