Approximately 2/3 of cardiovascular diseases in the Asia-Pacific region are closely associated with hypertension.1 And statistics indicates the existence of 160 million hypertension patients in China in 2004 with approximately 1 billion patients simultaneously suffering from other cardiovascular diseases.2 It is evident that hypertension control plays a crucial role in the prevention of cardiovascular disease. This study aimed to find the epidemiological features of hypertension in Heilongjiang province and to gather statistical information about the prevalence and causative factors of hypertension.
Using the stratified chunk method, investigators of this study completed a survey form, physical examination, and laboratory analysis of 10 620 participants (4691 males and 5929 females), who aged 15 years and above, being permanent residents from both rural (Lanxi) and urban area (Nangang District of Harbin) of Heilongjiang province from January 1 to February 28 in 2007. The participants were those without stress of fever, acute infection, history of operation, trauma, etc. They were divided into 15-, 25-, 35-, 45-, 55-, 65-, and ≥75-year age groups.
The investigators consisted of cardiologists, PhD students, and MSc students from the First Affiliated Hospital of Harbin Medical University as well as related physicians from local hospitals. Following the completion of the training program, the investigators started to investigate the participants from both urban and rural areas.
According to a widely accepted standardized protocol as well as quality control regulation, the investigators measured blood pressure, height, and body weight of the participants.
Blood pressure was measured using a mercury sphygmomanometer under the circumstance of bright, silence and at room temperature (about 21°C), no smoking 15 minutes before examination, and no movement and stress 5 minutes before examination. Systolic and diastolic pressure was measured according to Korotkoff sounds. Specifically, systolic pressure was identified using a mercury sphygmomanometer when the first sound was heard; diastolic pressure was identified when the fifth sound disappeared. The measurement was repeated three times with the average value being calculated based on the second and third measurements. The criteria for diagnosis of hypertension were the 2005 revised China Guidelines for the Management of Hypertension. The accuracy rate of blood pressure was 1 millimeter of mercury.
Height and body weight were measured using standard instruments. In addition, body mass index (BMI) was also assessed (BMI=weight (kg)/height2 (m2)). The criteria for diagnosis were identified as follows: BMI ≥24 was considered overweight; BMI ≥28 was considered obese. The accuracy rate of height and body weight was 0.01 m and 0.1 kg respectively.
A 5-ml venous blood sample was taken from each participant who had fasted for 8-10 hours. Total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), and high density lipoprotein cholesterol (HDL-C) were examined by the endpoint method in the blood sample (TARGA-2000 Automatic Biochemistry Analysator, Italy).
Data were double entered and validated using Epidata
3.02 software. Categorical variables were expressed as rates or proportions and were compared using the chi-square test. We analyzed risk factors by the Logistic regression model. A 2-sided P value less than 0.05 was considered statistically significant. All the data were analyzed by SAS 9.1.3 statistical software package.
In 11 216 participants we investigated (aged 15 years and above, permanent residents in both rural and urban areas of these regions), 10 620 (4691 males and 5929 females) responded with a rate of 94.69%. Those who lost to follow-up included the participants going out for jobs, going to colleges, traveling or refusing examination.
Hypertension prevalence in Heilongjiang province in 2007 is shown in Table 1. The prevalence of hypertension in urban and rural areas was 31.30% and 29.65% respectively. The prevalence of hypertension in this province was 30.48% (adjusted prevalence was 25.69%). The prevalence of hypertension in males was higher than in females in both urban and rural areas. The comparison of our results with the national database suggested that Heilongjiang province is a region with a high prevalence of hypertension (i.e., prevalence of hypertension in this region was 25.69%), significantly higher than the average (18.81%) in China in 2004.
As indicated in Table 2, the prevalence of hypertension increased progressively with age accompanied by a trend of earlier onset age. Data demonstrated that the prevalence of hypertension was higher in males before the age of 55 years (P <0.0001); whereas, among the people older than 55 years, the prevalence in females increased rapidly. This was not different in the prevalence of hypertension in participants aged 65 years and over (P >0.05).
The prevalence of hypertension varied among participants with different professions. In this investigation, farmers and service staff had the lowest prevalence; whereas, office staff had the highest prevalence. Technical professionals possessed a median prevalence of hypertension. The prevalence of hypertension for the office staff was as high as 41.67%, suggesting that they should be a target population for hypertension prevention and treatment.
Using the Logistic model, we analyzed hypertension- related factors and identified BMI (OR 1.945), gender (OR 1.912), increased TG (OR 1.757), age (OR 1.669), decreased HDL-C (OR 1.390), and genetic history (OR 1.184) as the contributing risk factors for hypertension in Heilongjiang province (Table 3). Hypertension prevalence (59.64%) in participants with BMI >28 was much higher than that of participants with BMI between 24 and 28 (38.06%, P <0.0001) and BMI <24 (17.52%, P <0.0001).
In this investigation, hypertension prevalence was found to be related to education background. The highest prevalence was identified in the uneducated population (45.44%). People with primary school education had a relatively high prevalence (34.81%) of hypertension. The lowest prevalence (18.15%) was found in people with undergraduate education. The participants graduating from high schools and technical schools had an intermediate prevalence.
The prevalence of hypertension was higher in alcoholic participants in comparison with the non-alcoholic group (P <0.01) and gradually increased with the rise of alcohol uptake. Furthermore, we discovered that diastolic pressure was significantly elevated (5 mmHg higher than the non-alcoholic group, P <0.01) at an alcohol uptake of 1.1-1.5 kg/month. When alcohol uptake increased to 3.0 kg/month, diastolic pressure was 9.7 mmHg higher than that in the non-alcoholic group (P <0.01). Participants with a history of smoking in this investigation had a higher prevalence (40.19%) of hypertension in contrast to the general prevalence (25.69%, P <0.01). However, our results indicated that daily cigarette consumption was not correlated with the prevalence of hypertension.
Family history was identified as one of the important factors contributing to hypertension. We found that participants with a history of maternal hypertension had a higher prevalence (37.88%) than those without a history (31.93%, P <0.0001), suggesting a role of hereditary predisposition in the development of hypertension.
This investigation revealed that the hypertension awareness rate was 48.9%, treatment rate 25.33% and control rate 4.32%.
In the present investigation, we found the epidemiological characteristics of hypertension and its risk factors in Heilongjiang province.
In comparison with the national survey in 2004,3 the prevalence of hypertension in Heilongjiang province was higher than the average level in China. Hence, Heilongjiang province could be considered a high-risk area of hypertension. The harsh climate and diet in this region may be primary factors for the high prevalence of hypertension.4 Consumption of salt has also been universally accepted as a risk factor for hypertension.5 The average daily salt uptake for residents in Heilongjiang province was 17-18 g/d, which was significantly higher than the average level in China,4 suggesting that high salt uptake may be another reason for the high prevalence of hypertension in Heilongjiang province.
The present investigation revealed that the prevalence of hypertension in Heilongjiang province has reached 25.69%. Hypertension in the younger population may be due to the combined effects of heredity, abnormal metabolism, and an unhealthy lifestyle. These factors act synergistically, causing elevation of blood pressure, endothelial dysfunction, cardiac remodeling, abnormal metabolism, and destruction of organ function, eventually leading to cardiovascular events.6
The prevalence of hypertension was significantly higher in male than in female participants before the age of 55 years. However the prevalence in female participants rapidly increased after the age of 55 years, and the difference of hypertension prevalence between the two genders disappeared in participants older than 65 years. This may be associated with the protective effect of estrogen on the cardiovascular system and that of unhealthy lifestyle of the male population such as drinking and smoking.7
Alcohol consumption was also found to be positively correlated with diastolic pressure. This correlation was not altered in those who received anti-hypertension drug treatment.8 It has been established that alcohol functions to reduce the risk of coronary disease through increasing serum concentration of HDL, suppressing inflammation and altering the sensitivity of insulin. Consequently, rather than complete abstinence from alcohol, hypertension patients could drink appropriately and avoid massive drinking, which normally leads to the sudden elevation of blood pressure. Smoking is another independent risk factor for hypertension.9 The current investigation revealed that the prevalence of hypertension in the population with a history of smoking was significantly higher than the general prevalence.
The present investigation showed the highest prevalence in participants who dropped out of primary schools. The prevalence of hypertension was also high in the population with only primary school education. The population with undergraduate education had the lowest prevalence. The participants graduating from high schools and technical schools had an intermediate prevalence. The overall less occurrence of risk factors such as unbalanced diet, obesity, smoking, alcoholism, and lack of education may be the main reason for the observed lower prevalence of hypertension in this population.10 In this investigation, government and business executives were found to have a high risk factor for hypertension, with a prevalence of 41.67%. This phenomenon may be associated with a faster occupational pace, mental stress, unhealthy lifestyle and diet, and lack of exercise.11
This investigation also demonstrated that the prevalence of hypertension in the population with a 28 or above BMI reached 59.64%, indicating that higher BMI is a high risk factor for hypertension. Although the mechanisms underlying abdominal fat-causing hypertension remain unclear, they may be associated with abnormal endothelial function, renal damage, and activation of the sympathetic nervous system and renin-angiotensin system.12 By multi-linear analysis, we also identified a correlation between hypertension and increased TG and reduced HDL. We also found that the prevalence of hypertension is higher in the population with maternal hypertension history than that in the population without.
Awareness, treatment, and control rate of hypertension are tightly linked to patients' prognosis. In the present investigation, awareness, treatment, and control rates were found lower than the average levels reported in China and in USA.13,14
In conclusion, Heilongjiang province is the “high-risk” region for hypertension and should be considered an important target area for nation-wide hypertension prevention and treatment.
We thank LI Bin from the Health Department of Heilongjiang Province, ZHOU Jin from the First Affiliated Hospital of Harbin Medical University, HU Wei-fang from the Health Department of Nangang District of Harbin, QU Gui-rong and ZHOU Guang-wei from the Ninth Hospital of Nangang District of Harbin for their contribution and financial support. We are also grateful to the 100 graduate students and related doctors involved in the project for their hard work.
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