Prevalence, Awareness, Treatment and Control of Hypertension in Northern China: a Cross-Sectional Study

doi:10.21203/rs.3.rs-38795/v3

Background: Hypertension has always been a worldwide health concern. The purpose of this study was to investigate the prevalence, awareness, treatment, and control rates of hypertension among adult residents of northern China, where people usually have a high-fat, high-salt diet and heavy alcohol consumption.

Methods: Through the Early Screening and Comprehensive Intervention Project for High Risk Groups of Cardiovascular Diseases in the Inner Mongolia Autonomous Region of northern China, we collected data of 70,380 residents, from September 2015 to June 2017. We assessed the prevalence, awareness, treatment, and control of hypertension in the total population and subpopulations.

Results: Among participants, only 13.4% had optimal blood pressure levels. About 55.7% (95% confidence interval (CI): 55.3%–56.1%) of the participants had hypertension. The national standardized and the regional standardized prevalence rate was 49.4% and 55.4%, respectively. Multivariate logistic regression showed that old age, male, Han, living in rural, farmer, current drinker, not married, diabetes, obesity and dyslipidemia were associated with hypertension. In addition, the awareness, treatment, control and control under treatment rate of hypertension were 52.8% (95% CI: 52.3%–53.3%), 43.3% (95% CI: 42.8%–43.8%), 8.6% (95% CI: 8.3%–8.9%) and 19.8% (95% CI: 19.2%–20.4%), respectively. And the 70,380 population subgroups varied with respect to hypertension prevalence (range 32.6%-73.4%), awareness (35.1%-76.2%), treatment (24.9%-64.6%), control (3.9%-20.4%), and control under treatment (11.2%-31.6%). Controlled hypertension were less common in those younger age, Mongol, not married, farmer and current drinker.

Conclusion: Most patients of hypertension are going undetected and uncontrolled in northern China. Even if patients with hypertension are under treatment, hypertension can remain inadequately controlled.

Cardiothoracic Surgery

Cardiac & Cardiovascular Systems

Hypertension

Blood pressure

Prevalence

Epidemiology

Hypertension is a leading health risk^1,2. Hypertension contributes to 51% of stroke deaths and 45% of ischemic heart disease deaths worldwide³ and causes more than 7 million premature deaths each year⁴. The Global Burden of Disease study 2019 indicated that high systolic blood pressure (SBP) accounted for 10.8 million deaths and was responsible for the largest number of all-cause deaths⁵. Studies have shown that the global prevalence of hypertension has risen continuously in recent decades, especially in low-income and middle-income countries^6,7. It is estimated that 26.4% (972 million) of adults had hypertension in 2000, and the number in 2025 is predicted to increase by about 60%, to a total of 1.56 billion globally⁸. The number of Chinese adult patients with hypertension increased from 153 million in 2000 to more than 270 million in 2012⁹. A national study during 2014-2017 showed that 44.7% of Chinese adults aged 35-75 years had hypertension¹⁰. However, the level of hypertension management remains suboptimal in China, with fewer than half of patients with hypertension in China receiving treatment and fewer than one-fifth with controlled blood pressure^11-1⁴.

Studies have shown that the prevalence of hypertension in southern China is lower than that in the northern part of the country¹³^,1⁵. Because Inner Mongolia lies across a large part of northern China, it is somewhat representative of this region, where people have a high-fat, high-salt diet and heavy alcohol consumption¹⁶. However, previous studies have covered a limited area and have included a small sample size, and most studies have not linked blood pressure with demographic characteristics and clinical variables of different populations. The disease burden of hypertension in northern China remains unclear and identifying adverse factors involved in hypertension is urgent. Thus, obtaining reliable information about the prevalence, awareness, treatment, and control of hypertension is critical for further prevention and control of this disease and diseases secondary to hypertension.

Accordingly, in this study, we aimed to provide updated and reliable data on the hypertension prevalence, awareness, treatment, and control of the total population and subpopulations in northern China’s Inner Mongolia, and to identify the factors associated with prevalence and control of hypertension.

Study population

The study comes from the Early Screening and Comprehensive Intervention Project for High Risk Groups of Cardiovascular Diseases in Inner Mongolia. Multistage cluster sampling method was used to recruit the study population, from September 2015 to June 2017. In the first stage, 6 sites (Hohhot, Wuhai, Chifeng, Erdos, Hulun Buir, and Xingan League) were selected from the Inner Mongolia, according to the economic level, geographical location, and distribution of ethnic minority nationalities, etc. In the second stage, the local Centre for Disease Control and Prevention then identified one district or county at each site based on the urban-rural distribution and population stability. In the third stage, two or three urban residential communities or rural villages were selected from each of districts or counties according to the size of communities or villages. In the final stage, invite the residents from each of the communities or villages to participate in the study through extensive publicity on television, broadcast and in the newspaper. The study population comprised 70,380 participants who were aged 35-75 years and lived there for at least 6 of the previous 12 months. This project was approved by the ethics committee of Fuwai Hospital Chinese Academy of Medical Sciences (approval number: 2014-574), and all participants gave their written informed consent.

Measurement

We used a self-designed questionnaire and trained medical personnel conducted face-to-face interviews. The questionnaire mainly included demographic characteristics such as age, ethnic groups, education, marital status, annual Income，health insurance, history of disease, and lifestyle factors including smoking and drinking. Information on height, weight, blood pressure, and fasting blood glucose was obtained in physical or laboratory examinations.

For each participant, Blood pressure was measured by electronic blood pressure monitor (Omron HEM-7430; Ormon Corporation, Kyoto,Japan) two times on right upper arm after at least 5 minutes of rest in a seated position. If the SBP or DBP difference is >5 mmHg, the third time is measured, and the average blood pressure value of the two or three readings was used. The height and weight of the participants were measured using a calibrated height and weight instrument. Before the measurement, the subject removed the shoes and hats, took out the weight in the pocket, stood upright when standing, straightened the back, and naturally sagged. The eyes are looking straight ahead and the values are recorded after the values are stable. After at least 10 hours of overnight fasting, venous blood samples were collected for the measurement of blood glucose. Blood glucose was measured by a glucose analyser (BeneCheck PD-G001-2, Taiwan, China).

Definition

Hypertension was defined as an average SBP ≥140 mmHg, or average diastolic blood pressure (DBP) ≥90 mmHg, or self-reported use of antihypertensive medications in the previous 2 weeks. Awareness was defined as a self-reported hypertension history or self-reported use of antihypertensive drugs among patients with hypertension. Treatment of hypertension was defined as use of antihypertensive medication among participants with hypertension. Control of hypertension was defined as an average SBP <140 mmHg and an average DBP <90 mmHg among patients with hypertension. Control under treatment was defined as an average SBP <140 mmHg and average DBP <90 mmHg after using antihypertensive medication among patients with hypertension. According to the 2018 Revision of Chinese Guidelines for Hypertension Prevention and Control, optimal blood pressure is defined as an average SBP 90-119 mmHg and DBP 60-79 mmHg. High–normal, stage 1, stage 2, and stage 3 are defined as average SBP 120-139 mmHg or DBP 80-89 mmHg, SBP 140-159 mmHg or DBP 90-99 mmHg, SBP 160-179 mmHg or DBP 100-109 mmHg, and SBP ≥180 mmHg or DBP ≥110 mmHg, respectively. If SBP and DBP had different grades, the higher grade was chosen.

Body mass index (BMI) was defined as weight in kilograms (kg) divided by height in meters squared (m²). Obesity was defined as a BMI of at least 28 kg/m², according to recommendations of the Working Group on Obesity in China. Diabetes was defined as use of hypoglycemic medication or a measured fasting blood glucose level ≥7.0 mmol/L or non-fasting blood glucose level ≥11.1 mmol/L. Current drinker referred to drinking alcohol at least 1 time/month in the previous 1 year. Current smoker was defined as smoking at least 1 cigarette every day.

Statistical analysis

Statistical analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC, USA). Based on data of the sixth national census of China 2010 (National Bureau of Statistics), the age- and sex- standardized rates of hypertension prevalence at national level were calculated by the direct method. Since the subjects of our study had asymmetrical structure of location of residence and ethnicity when compared to the data from the total population of Inner Mongolia, standardized rates of hypertension at regional level were calculated based on age, gender, location of residence, and ethnicity using the direct method of standardization and standard population came from the 2010 statistical yearbook of Inner Mongolia (Inner Mongolia Autonomous Regional Bureau of Statistic). Continuous variables were expressed as mean and standard deviations (SD) and compared using the analysis of t test, t’ test, or Wilcoxon rank sum test. Categorical variables were reported as frequency and proportions. Proportions were compared using the Pearson Chi-square test or Trend Chi-square tests. To analyze the association between individual characteristics and prevalence as well as control of hypertension, multivariate logistic models were developed with stepwise selection of independent variables. A two-sided P value <0.05 was considered statistically significant.

A total of 70,380 participants aged 35–75 years were included in the study. Characteristics of the study population are shown in Table 1. Among participants, 58.0% were female, the mean age was 54.4 (SD: 9.4) years. The mean SBP and DBP was 140.5 (SD:20.9) mmHg and 84.8 (SD:11.6) mmHg, respectively. The prevalence of diabetes was 19.5% and the mean BMI was 25.8 (SD:3.6) kg/m².

Table 1. Baseline characteristics of the study population

Characteristics	All subjects (N=70,380)
Age (years), Mean±SD	54.4±9.4
Blood pressure(mmHg) , Mean±SD
SBP	140.5±20.9
DBP	84.8±11.6
BMI(kg/m²) , Mean±SD	25.8±3.6
Normal, n(%)	5294(7.5)
Overweight, n(%)	47588 (67.6)
Obesity, n(%)	17498 (24.9)
Gender, n(%)
Male	29539 (42.0)
Female	40841 (58.0)
Location of residence, n(%)
Rural	48695 (69.2)
Urban	21685 (30.8)
Marital status
Married	64203 (91.2)
Not married	6177 (8.8)
Ethnicity, n (%)
Han	63172 (89.8)
Mongolian	6086 (8.6)
Others	1122 (1.6)
Annual household income, n(%)
<10000(yuan)	19716 (28.0)
10000-50000(yuan)	36980 (52.6)
>50000(yuan)	8044 (11.4)
Unknown	5640 (8.0)
Educational level, n (%)
Primary school or lower	28466 (40.5)
Middle school	30576 (43.4)
High school	7814 (11.1)
Unknown	3524 (5.0)
Farmer, n (%)	33186 (47.2)
Health insurance, n(%)	61139 (86.9)
Diabetes, n (%)	13707 (19.5)
Current smoker, n (%)	17624 (25.0)
Current drinker, n (%)	19089 (27.1)

Data are reported as n(%) or mean ± SD. Abbreviations: SD, standard deviation; SBP, Systolic blood pressure; DBP, diastolic blood pressure; BMI, body mass index.

Mean blood pressure levels and distribution of blood pressure

Figure 1 shows gender- and age-specific mean blood pressure values for the all participants and for 3 subgroups defined by hypertension status. Overall, the mean SBP increased gradually with age throughout entire age range, whereas the mean DBP decreased in 65-75 age group. Overall, the mean SBP and DBP among participants with hypertension were 30.95 (95% CI: 30.62-31.27) mmHg and 13.63 (95% CI: 13.44-13.83) mmHg lower than the corresponding values among those with treated hypertension, and 38.33 (95% CI: 37.76-38.89) mmHg and 18.27 (95% CI: 17.90-18.63) mmHg lower than the corresponding values for those with untreated hypertension. The overall SBP and DBP differences between treated and untreated participants with hypertension were 7.38 (95% CI: 6.75-8.01) mmHg (t’=-20.644, P<0.001) and 4.64 (95% CI: 4.24-5.03) mmHg (t’=-22.999, P<0.001), respectively.

The percentage distribution of blood pressure levels among study participants is shown in the Figure 2. Overall, only 13.4% of the study population (11.5% of men and 14.7% of women) had optimal blood pressure, whereas nearly two-fifths (38.8%) had high normal blood pressure. The prevalence of stage 1, 2, and 3 hypertension was 30.7%, 10.7%, and 6.3% in male and 29.4%, 12.3%, and 6.2% in female, respectively. With increasing age, the percentage of optimal and high-normal blood pressure decreased whereas the proportion of stage 1, stage 2, and stage 3 hypertension increased (Trend Chi-square tests: male, =999.9, P<0.001; female, =41666.2, P<0.001).

Prevalence, awareness, treatment and control of hypertension

The prevalence, awareness, treatment, control and control under treatment of hypertension by different groups is showed in Table 2. The crude rates of prevalence awareness, treatment, control and control under treatment for hypertension was 55.7% (95% CI: 55.3%-56.1%), 52.8% (95%CI: 52.3%-53.3%), 43.3% (95%CI: 42.8%-43.8%), 8.6% (95%CI: 8.3%-8.9%) and 19.8% (95%CI: 19.2%-20.4%), respectively. The national standardized prevalence rate and the regional standardized prevalence rate was 49.4% (95%CI: 49.0%-49.8%) and 55.4% (95%CI: 55.0%-55.8%), respectively. The population subgroups varied with respect to hypertension prevalence (range: 32.6%-73.4%), awareness (range: 35.1%-76.2%), treatment (range: 24.9%-64.6%), control (range: 3.9%-20.4%), and control under treatment (range: 11.2%-31.6%).

Table 2. Prevalence, awareness, treatment, control, and control under treatment of hypertension among different groups, %(95%CI)^a

Groups	Prevalence	Awareness	Treatment	Control	Control under treatment
Crude rates	55.7(55.3-56.1)	52.8(52.3-53.3)	43.3(42.8-43.8)	8.6(8.3-8.9)	19.8(19.2-20.4)
Gender
Male	57.4(56.8-58.0)	49.7(48.9-50.4)	39.6(38.9-40.3)	8.2(7.8-8.6)	20.8(19.8-21.7)
Female	54.5(54.0-54.9)	55.2(54.5-55.8)	46.1(45.4-46.7)	8.8(8.5-9.2)	19.2(18.4-20.0)
Ethnicity
Han	56.0(55.6-56.4)	53.6(53.1-54.1)	44.2(43.7-44.7)	8.9(8.6-9.2)	20.2(19.6-20.8)
Mongol	52.7(51.4-53.9)	44.6(42.9-46.4)	34.2(32.6-35.9)	5.1(4.4-5.9)	15.0(12.9-17.2)
Others	53.2(50.3-56.1)	48.9(44.9-52.9)	38.9(35.0-42.8)	6.0(4.1-7.9)	15.5(10.9-20.2)
Age (years)
35-44	32.6(31.7-33.4)	35.1(33.6-36.6)	24.9(23.5-26.2)	5.3(4.6-6.0)	21.4(18.8-24.0)
45-54	50.6(50.0-51.3)	47.9(47.1-48.8)	38.1(37.2-38.9)	8.0(7.5-8.5)	21.0(19.8-22.2)
55-64	64.2(63.6-64.8)	56.9(56.1-57.7)	47.8(47.0-48.5)	9.5(9.0-9.9)	19.8(18.9-20.7)
65-75	73.4(72.5-74.2)	60.9(59.9-62.0)	51.6(50.5-52.7)	9.3(8.7-9.9)	18.0(16.9-19.2)
Marital status
Married	55.1(54.7-55.5)	53.0(52.5-53.5)	43.4(42.9-44.0)	8.9(8.6-9.2)	20.4(19.8-21.0)
Not married	62.0(60.8-63.2)	50.9(49.3-52.5)	41.8(40.3-43.4)	5.9(5.2-6.7)	14.2(12.5-15.9)
Farmer
Yes	56.7(56.2-57.3)	51.8(51.1-52.5)	41.4(40.7-42.1)	7.6(7.2-8.0)	18.4(17.5-19.3)
No	54.8(54.2-55.3)	53.8(53.1-54.4)	45.1(44.4-45.7)	9.5(9.1-9.9)	21.0(20.2-21.8)
Location of residence
Rural	56.0(55.6-56.5)	52.5(51.9-53.1)	42.4(41.8-43.0)	8.3(8.0-8.6)	19.5(18.8-20.3)
Urban	54.9(54.3-55.6)	53.6(52.7-54.5)	45.3(44.4--46.2)	9.2(8.7-9.8)	20.4(19.3-21.5)
Educational level
Primary school or lower	58.8(58.3-59.5)	54.3(53.6-55.1)	44.3(43.6-45.1)	8.0(7.6-8.4)	18.1(17.2-19.0)
Middle school	54.4(53.8-54.9)	53.2(52.4-53.9)	44.0(43.2-44.7)	9.5(9.0-9.9)	21.5(20.6-22.4)
High school	47.8(46.7-48.9)	49.8(48.2-51.4)	40.1(38.5-41.7)	9.5(8.5-10.4)	23.6(21.5-25.8)
Unknown	58.8(57.2-60.4)	43.3(41.2-45.4)	45.9(43.0-48.8)	11.2(9.3-13.0)	16.8(14.7-18.9)
Annual Income (RMB)
<10000	58.6(58.0-59.3)	53.7(52.8-54.6)	42.8(41.9-43.7)	8.2(7.7-8.7)	19.1(18.0-20.2)
10000-50000	54.4(53.9-54.9)	52.9(52.2-53.6)	44.2(43.5-44.9)	9.0(8.6-9.4)	20.3(19.5-21.1)
>50000	54.2(53.1-55.3)	53.8(52.3-55.3)	43.4(41.9-44.9)	9.2(8.4-10.1)	21.3(19.4-23.1)
Unknown	61.9(60.2-63.5)	47.6(45.9-49.4)	35.0(32.9-37.1)	3.9(3.1-4.8)	11.2(8.8-13.5)
Health insurance
Yes	55.5(55.1-55.9)	53.4(52.9-53.9)	43.8(43.3-44.3)	8.8(8.5-9.1)	20.0(19.3-20.6)
No	56.9(55.9-57.9)	49.0(47.7-50.4)	39.9(38.6-41.3)	7.4(6.7-8.1)	18.6(17.0-20.3)
Diabetes
Yes	70.2(69.4-70.9)	60.2(59.2-61.2)	50.8(49.8-51.8)	9.6(9.1-10.2)	19.0(17.9-20.1)
No	52.2(51.8-52.6)	50.4(49.8-51.0)	40.8(40.3-41.4)	8.2(7.9-8.5)	20.1(19.4-20.9)
Obesity
Yes	71.4(70.7-72.0)	60.7(59.8-61.5)	51.2(50.3-52.1)	8.9(8.4-9.4)	17.4(16.5-18.4)
No	50.5(50.1-50.9)	49.1(48.5-49.7)	39.6(39.0-40.2)	8.4(8.1-8.7)	21.2(20.5-22.0)
Current smoker
Yes	53.2(52.5-54.0)	50.7(49.7-51.7)	40.8(39.8-41.8)	9.4(8.8-10.0)	23.0(21.7-24.3)
No	56.6(56.1-56.9)	53.5(52.9-54.0)	44.1(43.5-44.6)	8.3(8.0-8.6)	18.9(18.2-19.5)
Current Drinker
Yes	57.0(56.3-57.7)	46.4(45.5-47.4)	34.9(34.0-35.8)	6.3(5.9-6.8)	16.0(14.8-17.1)
No	55.2(54.8-55.6)	55.3(54.7-55.8)	46.5(45.9-47.1)	9.4(9.1-9.8)	20.3(19.6-21.0)
Prior CVD
Yes	72.7(71.2-74.2)	72.0(70.2-73.7)	60.2(58.2-62.1)	14.5(13.1-15.9)	24.1(21.9-26.3)
No	54.8(54.4-55.2)	51.5(51.0-52.0)	51.5(51.0-52.0)	8.2(7.9-8.5)	19.4(18.8-20.0)
Prior CHD
Yes	68.4(65.8-71.0)	76.2(73.3-79.1)	64.6(61.3-67.8)	20.4(17.7-23.1)	31.6(27.7-35.5)
No	55.5(55.1-55.8)	52.3(51.8-52.8)	42.8(42.3-43.3)	8.3(8.0-8.6)	19.4(18.8-20.0)

^a: The value is presented in percent (95% confidence interval). Abbreviations: CVD, cardiovascular disease; CHD, coronary heart disease.

Hypertension was categorized as unaware of disease, aware but not treated, treated but not controlled, or controlled (Figure 3). In this study populations, hypertension patients accounted for 55.7%, of which 26.3% were unaware of disease, 19.3% were treated but not controlled, 5.3% were aware but not treated, and only 4.8% were controlled. The proportion of the hypertension patients and the proportion of each part increased with age. The control rate among patients with hypertension were very low among all age groups in both male and female.

The factors associated with prevalence and control of hypertension

Using the multivariate logistic model, we identified several significant determinants that were associated with prevalence and control of hypertension (Figure 4). Younger patients were less likely to suffer from and control hypertension whereas those aged 35-44 years had the lowest odds ratios of being hypertension and reaching the target for blood pressure. In addition, among all participants who had dyslipidemia, diabetes, obesity, Han, not married, current drinker, non-current smoker, were farmer, living in rural areas, were male and old age were significantly more likely to be suffered from hypertension. Patients who were farmer, Mongol, not married, current drinker, non-current smoker, young age, without obesity and without prior CVD were less likely to be controlled for hypertension.

To the best of our knowledge, this study presents the latest reliable information about the epidemiological situation of hypertension in Inner Mongolia, the largest province in northern China. In the first and largest population survey in Inner Mongolia, we precisely estimated the level of blood pressure, the current situation of hypertension, and the disease burden of hypertension in Inner Mongolia. In northern China, Inner Mongolia, the rates of prevalence, awareness, treatment, control and control under treatment for hypertension was 55.7%, 52.8%, 43.3%, 8.6% and 19.8%, respectively. And the rates of prevalence, awareness, treatment, control and control under treatment for hypertension varied widely across the various subgroups, from 32.6% to 75.1%, from 35.7% to 76.2%, from 24.9% to 64.6%, from 3.9% to 20.4%, and from 11.2% to 31.6%.

We found that hypertension with high prevalence and low control in northern China, which was similar to the results of other previous studies from in Inner Mongolia and northern China^11,17-20. And compared with studies from high-income countries^21,22，we observed higher prevalence and lower control rates of hypertension in northern China. Likewise, we found that the age- and sex-standardized rates of hypertension prevalence were higher than those in a 2017 report from national report (49.4% vs. 37.2%)¹⁰. The higher prevalence of hypertension were found in our study could be explained by obesity and high-salt diet, which were the main factors associated with hypertension. As well known, high-salt diet is common in Inner Mongolia. A survey in Inner Mongolia showed that the salt intake was 12.9 g/d, which was higher than the 7-8 g/d in southern China, and twice more than the recommended salt intake (less than 5 g/d) by World Health Organization (WHO)²³. The Global BMI Mortality Collaboration reported that overweight and obesity significantly increased the risk of all-cause death in the global population²⁴, and were important risk factors for hypertension^4,25,26 The obesity rate in this study was 24.9%, while the national study in the same period reported that the obesity rate of the 35-75years old population was 15.7%¹⁰. In addition, we found that most of the hypertension patients in the study were unaware and treated but not controlled. Even a study conducted in 44 low-income and middle-income countries showed that the lowest control rate of hypertension was 11.3% in Belize²⁷, which was higher than our study results (8.6%). And the rate of control under treatment for hypertension only was 19.8% in our study. Therefore, it is necessary to improve the discipline level and service capabilities of the grassroots units in Inner Mongolia by standardizing the procedure of diagnosis and comprehensive treatment and implementing comprehensive management and control strategies.

We found the obesity were associated with better blood pressure awareness, treatment and control among hypertensive patients. These findings are in agreement with He et al.’s reports²⁸. It has been suggested that obesity positively influence blood pressure checking and prescription of medication for intervention, hence, higher awareness, treatment and control levels.

The mean SBP and DBP was 140.5 mmHg and 84.8 mmHg in Inner Mongolia, respectively. The results of a cohort study showed that the mean blood pressure in northern China was SBP 122.7/DBP 80.0 mmHg and in southern China was 117.0/75.7 mmHg. Compared to our results, one study conducted in Jilin Province²⁵, which located in northern China and had similar economic level to Inner Mongolia, showed lower blood pressure level (130.5/85.0 mmHg in male, 128.3/81.7 mmHg in female). The difference in blood pressure between our study and other studies may partly attributed to the different age and eating habits of the study populations. In addition, we found that uncontrolled hypertension who were treated and untreated had a large distance to the target values of SBP, the distance were 18.0 (8.0-30.5) mmHg and 10.5 (3.0-20.5) mmHg, respectively. The results showed that populations had higher blood pressure in Inner Mongolia, especially SBP. A study has showed that the highest risk factor attributed to global death in 2019 was high SBP, which accounted for 19.2% of the total deaths⁵. There was closely causal relationship between blood pressure and the incidence and death of cardiovascular and cerebrovascular diseases. The SBP of Asians increased by 10 mmHg, and the risk of stroke and myocardial infarction increased by 53% and 31%, respectively²⁹. Therefore, achieving the treatment targets of blood pressure is a great challenge and very urgent in Inner Mongolia.

Our study showed that the older age was a factor associated with hypertension. Although participants of the 35-44 age group had the lowest prevalence of hypertension in our study, their prevalence was higher than the national prevalence of hypertension (32.6% vs. 22%), and the 35-44 age group constituted the largest proportion of populations with high normal blood pressure. If the blood pressure of these populations was not well controlled, it will further increase the burden of hypertension. Notably, younger patients had lower awareness, treatment and control rate of hypertension, but they had higher control under treatment rate of hypertension. Compared with older adult patients, younger patients lack health awareness, have fewer consultations with clinicians, have more bad habits, are less likely to adhere to prescribed medications, but they have lower blood pressure levels. If younger patients can adhere to regular medication, blood pressure can be well controlled. Moreover, most guidelines advocate screening for blood pressure from a relatively young age³⁰. However, in our study, the participants of 35-44 age group had the lowest hypertension awareness rate. Thus, screening strategies need to be designed to appeal to individuals of young age.

The results of research on the relationship between smoking, drinking and hypertension are inconsistent^31-33. Some studies showed that smoking had no clear relationship with hypertension. Many studies had shown that hypertension was related to the level of alcohol consumption³². However, our study demonstrated that current smoker was a protective factor for hypertension. This can be attributed to the fact that cross-sectional studies cannot determine the sequence of cause and effect and that more hypertension tend to change bad lifestyles, such as quitting smoking. Several studies have found that the risk of hypertension is much higher among male than female, and hypertension awareness, treatment and control in female is higher than in male, which was consistent with our research results^34,35. Compared to female, male are less concerned about health and have more bad habits. Male visit the doctor less often, have shorter consultations, and tend to see their physician later in the course of their illness than female³⁶. Moreover, we found rural-urban and ethnicity disparity in the prevalence and control of hypertension. Compared with urban areas, the hypertension with higher prevalence and lower awareness, treatment and control in rural areas. This suggests that patients with hypertension in rural areas groups should be given more attention in promoting awareness, treatment and improving the management of hypertension.

Because Mongol was the main minority ethnic group in Inner Mongolia, ethnicity of participants was categorized into three groups including Han Chinese, Mongol, and other minority ethnic groups. We found that the crude prevalence rate of Mongol populations was higher than Han populations (52.7% vs 56.0%), but there was no statistically significant difference of the age- and gender-standardized rate (48.0% vs 48.7%) in Inner Mongolia (Additional file 1). However, researches by Li et al^26,37. showed that Mongol populations have a higher prevalence of hypertension than Han populations. Different ethnic-specific genetic susceptibility, environmental exposures and the interactions between gene and environment may account for the different prevalence of hypertension³⁸. A study conducted in Inner Mongolia showed that rs13306673 is a genetic factor for hypertension in the Han population but not in Mongolian population³⁹. A further study between the hypertension and ethnic specific genetic susceptibility is urgently needed to clarify the observation.

In Inner Mongolia Autonomous Region, primary health services are in a state of higher demand for health services, but the utilization and resource allocation of primary health services are at a lower level than whole country⁴⁰. Therefore, the investment in the resources of the primary health service system and the utilization rate of services in the study region should be improved. Moreover, the system of tiered diagnosis and treatment for hypertension, has not been developed in Inner Mongolia, which could contribute to the standardized management of hypertension and enhance the efficiency of utilization of primary health resources. Actually, in the Inner Mongolia Autonomous Region, it is necessary to increase the input of health resources in healthcare institutions at all levels, strengthen regional health planning, so as to further rationally and optimize the allocation of medical resources, taking into account the needs of health services and the needs of health services.

In conclusion, the results of our study suggested that hypertension in northern China is a serious problem, especially lack of detect and control. Hypertension patients accounted for 55.7%, of which 26.3% patients were aware but not treated and 19.3% patients were treated but not controlled. There is a great challenge for preventing and controlling of hypertension in the primary care system of Inner Mongolia. Even in secondary prevention of hypertension, we found inadequate awareness and treatment of hypertension. Increasing the awareness, treatment and control of hypertension will reduce morbidity and mortality of cardiovascular diseases. Our study underscores the urgent need to develop national strategies aimed at improving the prevention, detection, and treatment of hypertension in China in an effort to avert a CVD epidemic, especially in Inner Mongolia.

Because this study was a cross-sectional study, the finding cannot be used to establish a conclusive cause-and-effect relationship between risk factors and hypertension. There are some limitations. First, blood pressure value was measured in a single visit, so its value, as well as the prevalence of hypertension based partly on the measured blood pressure, may have been overestimated. Second, the study did not use representative sampling because it was not possible with such rapid, large-scale recruitment. Based on data from the total population in the Inner Mongolia, we adjusted for the main asymmetrical characteristics of the study population, including age, gender, location of residence, and ethnic groups. The adjusted prevalence, awareness, treatment and control rates of hypertension are very close to the crude rate. Third, we would expect that the rates of prevalence, awareness, treatment and control were overestimated in our study due to the sampling bias, since the potential participants who were more concerned about their health were more inclined to respond to our study. In addition, because information about diet and exercise were unavailable in our study, the rate of treatment of hypertension could be underestimated, but the control rate would remain unaffected. Lastly, the members in a family who satisfied the inclusion criteria were selected as our study participants; as a result, the correlation of influencing factors within families may have affected the association estimation between influencing factors and hypertension.

SBP: Systolic blood pressure; CVD: Cardiovascular disease; CHD: Coronary heart disease; DBP: Diastolic blood pressure; BMI: Body mass index; SD: Standard deviation.

Additional file 1: Table 4. The prevalence, awareness, treatment, control and control under treatment of hypertension among the Han and Mongol.

Ethics approval and consent to participate

This project was approved by the ethics committee of Fuwai Hospital Chinese Academy of Medical Sciences (approval number: 2014-574). All participants gave their written informed consent.

Consent for publication

Written informed consent for publication was obtained from all participants.

Availability of data and materials

The data that support the findings of this study are available from Early Screening and Comprehensive Intervention Project for High Risk Groups of Cardiovascular Diseases of National Center for Cardiovascular Diseases, but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of National Center for Cardiovascular Diseases.

Conflicting Interests

The Authors declare that there is no conflict of interest.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, or publication of this article: This work was supported by the Ministry of Finance of China and National Health and Family Planning Commission of China; the Natural Science Foundation Program of Inner Mongolia Autonomous Region [grant numbers 2020MS08048]; and the Inner Mongolia Autonomous Region Health and Family Planning Commission Research Project [grant numbers 201701041].

Authors' contributions

XX and HB contributed the central idea. XX wrote the initial draft of the paper. XX, HB, HZ and LN analysed the data. The remaining authors contributed to refining the ideas, carrying out additional analyses and finalizing this paper. All authors gave final approval, and agreed to be accountable for all aspects of work ensuring integrity and accuracy (XX, HB, ZT, HZ, LZ, LN, TY, HD, XF, XZ).

Acknowledgements

We thank Yunfeng Xi, Liying Qiao, Ke Han ang Gai Hang of Inner Mongolia Centre for Disease Control and Prevention for their support.

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Prevalence, Awareness, Treatment and Control of Hypertension in Northern China: a Cross-Sectional Study

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