Many hypertension guidelines have been published mainly from Western countries to standardize the management of hypertension all over the world, however, the significance of hypertension, along with other cardio-metabolic risks, such as obesity, diabetes or dyslipidemia should differ among different races. This paper compares the relevance of hypertension, one of the most important cardio-metabolic risk factors, in Asian and Western societies.
1) Low target level of blood pressure control for diabetic hypertensives in Japan
In the Japanese Society of Hypertension Guidelines for the management of Hypertension (JSH2014), the target of blood pressure (BP) control in hypertensive patients with diabetes was set as < 130/80 mmHg. This target is lower than that of major hypertension guidelines in Europe (ESH/ESC2013) and the United States (ADA2016, JNC-8).
The results of HOT and UKPDS38 gave the evidence for setting a lower BP target for diabetic hypertensive patients, and the recommendations of the American Diabetes Association (ADA) in 2003, JNC7 (2003) and ESH/ESC 2007 Guidelines set < 130/80 mmHg as a target level of BP control. The JSH 2009 Guidelines also set the same target.
However, in the ACCORD-BP in 2010, BP was reduced to 119.3/64.4 mmHg in the strict treatment group and to 133.3/70.5 mmHg in the standard treatment group. The annual incidences of a primary endpoint (nonfatal myocardial infarction (MI), nonfatal stroke, cardiovascular death) in the strict and standard groups were 1.87% and 2.09%, respectively, showing no significant difference (p = 0.20). A meta-analysis of 13 studies for 37,736 patients with diabetes/impaired glucose tolerance by Bangalore et al. also indicated that there was no positive reason to set the target BP level < 130/80 mmHg. ADA, thus, revised the target of BP control in diabetics to < 140/80 mmHg in 2013. In the ESH/ESC 2013 Guidelines, the target of BP control in diabetics was also revised to < 140/85 mmHg.
In Europe and the United State, the incidence of MI is higher than that of stroke, however, in Japan, the incidence of stroke is higher than that of MI. In the ACCORD-BP, the incidence of cerebral infarction was about one-quarter that of MI. On the other hand, in the Hisayama Study, the Suita Study and Japan Diabetes Complications Study, all of which were conducted in Japan, the incidence of cerebral infarction was 1.5–2.5 times higher than that of MI. In the ACCORD-BP, the hazard ratio of stroke was 0.59 in the strict control group, showing a significant decrease (p = 0.03), although the incidence rate was low. The meta-analysis of 13 studies by Bangalore et al. also indicated that stroke could be more effectively prevented at systolic BP level as low as < 120 mmHg.
In Japan, as well as other Asian countries, where stroke is prevalent, it may be appropriate to establish the target level of BP control as < 130/80 mmHg.
2) The significance of hypertension in Asia
The impact of cardio-metabolic risks, i.e., high BMI, high BP, decreased high-density lipoprotein cholesterol, high triglyceride, and high glycated hemoglobin (HbA1c), on cardiovascular diseases (CVD) mortality was compared between the USA (National Health and Nutrition Examination Survey III) and Japan (NIPPON DATA). It was shown that obesity, high BP, triglyceride, and HbA1c were the major risk factors in the USA, whereas only high BP and HbA1c level were significant in Japan. Since the prevalence of obesity was much higher in Western countries than in Asia, the relative importance of hypertension compared with obesity for CVD is higher in Asian than Western countries.
The Asia Pacific Cohort Studies Collaboration, which involved more than 500,000 individuals, demonstrated that the increase of the incidence of stroke by the same increase of BP was greater by two-fold in Asians than in Caucasians. In contrast, the increase of the incidence of coronary heart disease (CHD) was almost the same.
3) Salt consumption
In 2010, the estimated mean level of global sodium consumption was 3.95 g per day. This was nearly twice the WHO recommended limit of 2 g/day and equivalent to 5 g/day of salt. In Japan, the mean salt intake still exceeds 10 g per day. Sodium intakes were highest in East Asia, Central Asia, and Eastern Europe (> 4.2 g/day) in the world.
Salt restriction tends to inhibit stroke more than CHD. This may be because the effect of BP elevation on stroke is marked, whereas factors other than BP, such as diabetes or dyslipidemia, also contribute to the occurrence of CHD. Considering that stroke is prevalent in Asia, salt restriction should be quite efficient for the prevention of CVD in Asia than in Western societies.
4) Obesity and hypertension
Both in Asians and Caucasians, subjects with higher BMI and waist circumference show a higher prevalence of hypertension and diabetes. However, the susceptibility to abdominal obesity and the effect of obesity on hypertension or diabetes are different. Epidemiological studies demonstrated increased prevalence of abdominal obesity and increased prevalence of risk factors at lower BMI in Asians compared with Caucasians. With slight increase of BMI, Asians easily develop insulin resistance, which causes hypertension and diabetes. In addition, for any given level of BMI or waist circumference, the absolute risks for hypertension and diabetes tend to be higher among Asians compared with Caucasians.
These findings support the need for lower anthropometric cut-off points (the values derived from the ROC analysis that maximize the sum of sensitivity and specificity) for the discrimination of hypertension and diabetes in Asians. For example, the Obesity in Asia Collaboration recommends cut-off points of BMI in men as follows: 24 in Asians and 28 in Caucasians for the discrimination of diabetes, 24 for Asian and 27 for Caucasians for the discrimination of hypertension.
Hypertension is especially important risk factor in Asia, since the incidence of stroke is higher than that of MI, with high salt intake. Stroke can be prevented efficiently by strict BP control. Therefore, we, Asians, need our own hypertension guidelines, based upon our own characteristics.