Prevalence,awareness,treatment and control of hypertension among adults in rural north-western China: a cross-sectional population survey

Abstract

Objective

To assess rates and determinants of prevalence, awareness, treatment and control of hypertension in rural north-western China.

Methods

Adults were recruited from five surveillance areas in Gansu Province using a three-stage cluster sampling plan. A combination of household and community–based surveys was employed and two methods of surveillance (questionnaire and physical measurement) were undertaken.

Results

A total of 3000 subjects were included; 1100 (36.7%) had hypertension. Hypertension was associated with older age, lower educational levels and being overweight or obese. Only 407 (37%) subjects with hypertension were aware of their condition. Multiple logistic regression showed significant correlations between hypertension awareness and age, obesity and central obesity. Antihypertensive treatment was received by 31.2% of participants with hypertension. Obesity, smoking and older age were associated with treatment. Blood pressure was controlled in 18.1% of participants receiving antihypertensive treatment and in 5.6% of subjects with hypertension overall.

Conclusion

In conclusion, prevalence of hypertension is rapidly increasing in rural north-western China. Rates of awareness and treatment of hypertension remain low and blood pressure is poorly controlled.

Keywords

Hypertension awareness control cross-sectional survey prevention

Introduction

Hypertension is an important public health problem worldwide. It is one of the most common chronic diseases in China: according to the 2002 China National Nutrition and Health Survey (CNNHS) more than 153 million individuals over the age of 18 years were affected.¹ Quantitative evidence indicates that hypertension is the most widely recognized and important modifiable risk factor for cardiovascular disease and mortality.^2,3 Data from large-scale epidemiological surveys demonstrate a robust, continuous and causal association between increased blood pressure (BP) and cardiovascular disease.^4,5

Although treatable, the prevalence of hypertension in China is increasing,¹ and rates of awareness, treatment and control remain low.⁶ Of individuals with hypertension questioned as part of the 2002 CNNHS, only 24% were aware of their condition, 78% of affected individuals were receiving treatment and only 19 % were adequately controlled. Another survey conducted between 2005 and 2007 in rural Liaoning province, north-eastern China found the prevalence of hypertension to be 37.8 % in adults aged 35 – 85 years; only 29.5% of patients with hypertension were aware of their high BP, 20.2 % were taking antihypertensive medications and 0.9 % had achieved BP control (<140/90 mmHg).⁶ Among all the individuals surveyed, 43.9% did not believe that high BP was life-threatening. The benefits of treatment and control of hypertension in decreasing the risk of cardiac and cerebrovascular outcomes are well-established.⁷ Experience from developed countries shows that concerted public-health efforts are required to detect, treat and control hypertension at the community level.^8,9

Although previous studies have addressed the determinants of awareness, treatment and control of hypertension in other countries,^10–14 such data are not available for adults (≥18 years) living in north-western China. Different populations have different specific determinants of hypertension and for this reason it is inappropriate to directly extrapolate data from other countries or districts. Information regarding awareness, treatment and control of hypertension and correlations between these factors is critical in the identification and appropriate management of high-risk patient subgroups. The aim of the present study was to identify and quantitate the determinants of prevalence, awareness, treatment and control of hypertension using a combination of household and community–based surveys in a representative sample of rural adults in north-western China.

Subjects and methods

Study population

Subjects aged 18 – 85 years were sampled from five surveillance areas (Jingtai county, Lintan county, Maiji district, Ganzhou district and Dunhuang city) in Gansu Province, China between July 2010 and December 2010. The following three-stage cluster sampling plan was used to recruit participants: (i) three townships or streets were selected in each surveillance area; (ii) four villages or communities were randomly selected in each township or street (one village group or resident group of ≥50 households); (iii) ≥50 households were identified by simple randomized sampling in each selected village or resident group. For each household included, one subject was selected by the Kish grid method.¹⁵

The study was approved by the Ethics Committee of the Chinese Centre for Disease Control and Prevention and written informed consent was obtained from all subjects.

Survey methods and physical examination

A combination of household and community–based surveys was used. There were two methods of surveillance: a questionnaire and physical measurement. The questionnaires were completed by trained investigators from local Centres for Disease Control and Prevention in face-to-face interviews.

Anthropometric measurements were undertaken in all subjects and involved measures of height, weight and BP. For height measurement, subjects stood bare-foot on a portable standiometer (accuracy within 0.1 cm). Weight was measured in light clothing by electronic digital scales (accuracy within 0.1 kg). Before each measurement, the weight and height scales were checked and calibrated. BP was measured in the right arm using a digital sphygmomanometer (Omron 770 A, Omron Healthcare® Inc., Lake Forest, IL, USA). Three systolic/diastolic BP measurements were taken in each participant according to 1999 World Health Organization (WHO)/International Society of hypertension guidelines for the management of hypertension.¹⁶ Subjects rested in a seated position for 5 min prior to measurement of BP, their right arm was then placed at heart level and BP recorded. The first systolic and diastolic BP readings were excluded and the mean of the last two readings were used for analyses. Nurses taking the measurements were appropriately trained and evaluated.

Outcome measures

The following characteristics were defined: (i) level of education, recorded as completed years of schooling (≤6, 6 – 12 and ≥12 years); (ii) body mass index (BMI), calculated as body weight divided by height squared (kg/m²); (iii) overweight and obesity, assessed using WHO recommended BMI cut-off points where obesity is defined as a BMI of ≥30 kg/m² and overweight is defined as a weight of 25.0 – 29.9 kg/m²; (iv) current smoking, defined as daily smoking (yes/no); current alcohol consumption, defined as drinking in the last 12 months (yes/no); (v) waist circumference, defined as high (>95 cm for men and >90 cm for women), middle (>85 cm for men and >80 cm for women) and low (<85 cm for men and <80 cm for women); (vi) presence of hypertension, defined as mean systolic/diastolic BP ≥ 140/ ≥90 mmHg or self-reported current use of prescribed antihypertensive medication; (vii) awareness of hypertension, defined as participants having been told that they had hypertension by a healthcare professional; (viii) treatment of hypertension, defined as self-reported current use of prescribed medication; (viiii) control of hypertension, defined as mean systolic/diastolic BP <140 mmHg/BP <90 mmHg in participants receiving pharmacological treatment for their hypertension.

Quality control

To ensure the quality of the survey, quality control networks to monitor survey efficacy were created by the provincial and local Centres for Disease Control and Prevention at each surveillance point. The responsibilities and roles of all participants were defined and a proposal for quality control was developed and implemented. All investigators were trained by qualified personnel before joining the field survey team. Questionnaires collected from the field were reviewed by team leaders before they were submitted to headquarters for data entry. The ratio of displaced population was controlled to less than 6%.

Statistical analyses

Statistical analyses were performed using SAS® statistical software, version 9.1 (SAS Institute, Cary, NC, USA). Questionnaire data were double-entered using Epi Info™ 2000 software (Centers for Disease Control, Atlanta, GA, USA) for Windows®. Frequencies are presented as percentages. Proportions and ratios were compared using Pearson’s χ²-test. A multiple logistic regression model was used to ascertain associations between awareness of hypertension, treatment, control, and risk factors such as age, sex, education, current smoking, alcohol consumption, BMI and waist circumference, and odds ratios (OR) and 95% confidence intervals (CI) were calculated. All tests were two-sided and statistical significance was set at P < 0.05.

Results

A total of 3000 residents were surveyed, including 1355 men (45.2%) and 1645 women (54.8%) with a mean ± SD age of 46.3 ± 14.2 years. Educational levels were low: 40% (n = 1200) of participants had elementary school or no formal education, 43% (n = 1290) had attended secondary school and 17% (n = 510) had a tertiary education. In the overall population, the proportion of participants who were overweight or obese was 29.8% (n = 894) and 4.5% (n = 135) respectively.

The prevalence of hypertension was similar in men and women (Table 1) and increased significantly with age (P < 0.001). Participants with lower educational levels and those who were overweight or obese were more likely to have hypertension (P < 0.001). According to multivariate regression analyses, hypertension was independently associated with being overweight, obesity, central obesity (as determined by waist circumference) and increasing age (Table 1).

Table 1.

Demographic characteristics of all subjects with hypertension and of subjects who were aware of their hypertension from five surveillance areas in north-western China.

Characteristic	Subjects with hypertension			Subjects aware of their hypertension
Characteristic	n (%)^a	Adjusted OR (95% CI)^b	Statistical significance^c	n (%)^a	Adjusted OR (95% CI)^b	Statistical significance^c
Total	1100 (36.7)	407 (37.0)
Total, age-adjusted^a	1100 (32.2)	407 (31.5)
Age, years	P < 0.001	P < 0.001
18–44	310 (21.8)	1.00	81 (26.1)	1.00
45–59	453 (44.2)	2.65 (2.19–3.19)	P < 0.001	173 (38.2)	1.69 (1.21–2.35)	P < 0.01
≥60	337 (60.5)	5.29 (4.18–6.70)	P < 0.001	153 (45.4)	2.27 (1.59–3.26)	P < 0.001
Sex	NS	NS
Female	606 (36.8)	1.00	228 (37.6)	1.00
Male	494 (36.5)	0.98 (0.78–1.24)	179 (36.2)	1.48 (1.04–2.11)	P < 0.05
Education	P < 0.001	P < 0.05
<6 years (elementary)	522 (44.0)	1.21 (0.94–1.57)	216 (41.4)	1.30 (0.86–1.95)
7–14 years (secondary)	407 (31.3)	0.95 (0.74–1.20)	129 (31.7)	0.88 (0.59–1.30)
≥15 years (higher)	171 (33.3)	1.00	62 (36.3)	1.00
Current smoking	1	NS	P < 0.05
No	800 (36.8)	1	312(39.0)	1
Yes	300 (36.2)	1.03 (0.81–1.32)	95 (31.7)	0.66 (0.45–0.96)	P < 0.05
Current alcohol consumption	NS	NS
No	1023 (36.8)	1.00	381 (37.2)	1.00
Yes	77 (35.3)	0.99 (0.71–1.37)	26 (33.8)	0.96 (0.56–1.65)
BMI, kg/m²	P < 0.001	P < 0.001
<25	553 (28.0)	1.00	168 (30.4)	1.00
25–29	445 (49.7)	1.94 (1.56–2.41)	P < 0.001	186 (41.8)	1.35 (0.96–1.89)
≥30	102 (76.7)	5.35 (3.24–8.81)	P < 0.001	53 (52.0)	1.97 (1.12–3.46)	P < 0.05
Waist circumference, cm	P < 0.001	P < 0.001
Low	476 (27.2)	1.00	138 (29.0)	1.00
Middle	401 (44.7)	1.56 (1.27–1.93)	P < 0.001	161 (40.1)	1.46 (1.04–2.07)	P < 0.05
High	223 (62.2)	2.03 (1.47–2.81)	P < 0.001	108 (48.4)	1.68 (1.06–2.67)	P < 0.05

Data expressed as n (%) of subjects.

Percentages are age-adjusted to Chinese census data for 2000

Adjusted for all other variables in the table.

Pearson’s χ²-test.

OR, odds ratio; CI, 95% confidence interval; BMI, body mass index; NS, not statistically significant (P > 0.05).

Of the 1100 participants with hypertension, only 407 (37%) were aware that they had the condition (Table 1). The rates of awareness increased significantly with age, BMI and waist circumference (P < 0.001). Awareness of hypertension was significantly greater in obese and overweight individuals than in those of normal weight (P < 0.001). A similar trend was observed according to waist circumference categories: participants with the largest waist circumferences were more frequently aware that they had hypertension than those with a waist circumference in the middle category (P < 0.001). Multiple logistic regression analyses supported significant correlations between hypertension awareness and obesity, central obesity and age (Table 1).

A total of 343/1100 (31.2%) participants with hypertension were receiving treatment, which was equivalent to approximately 84% of those aware of their condition (Table 2). Treatment for hypertension was generally infrequent across all age groups, both sexes and all educational levels. Older individuals and those who were not current smokers were significantly more likely to be receiving antihypertensive treatment (P ≤ 0.01). Obesity, smoking and increasing age were independently associated with treatment for hypertension according to multivariate regression analysis (P ≤ 0.05).

Table 2.

Demographic characteristics of subjects receiving treatment for hypertension and of subjects with hypertension controlled by treatment from five surveillance areas in north-western China.

Characteristic	Subjects treated for hypertension			Subjects with controlled hypertension
Characteristic	n (%)^a	Adjusted OR (95% CI)^b	Statistical significance^c	n (%)^a	Adjusted OR (95% CI)^b	Statistical significance^c
Total	343 (31.2)	62 (18.1)
Total, age-adjusted^a	343 (24.7)	62 (20.8)
Age, years	P < 0.001	NS
18–44	57 (18.4)	1.00	13 (22.8)	1.00
45– to 59	146 (32.2)	2.07 (1.44–2.97)	P < 0.001	26 (17.8)	0.89 (0.40–1.98)
≥60	140 (41.5)	3.19 (2.16–4.71)	P < 0.001	23 (16.4)	0.88 (0.37–2.10)
Sex	NS	NS
Female	196 (32.3)	1.00	36 (18.4)	1.00
Male	147 (29.8)	1.40 (0.97–2.03)	26 (17.7)	0.57 (0.26–1.27)
Education, years	P < 0.05	NS
<6 (elementary)	184 (35.2)	1.14 (0.74–1.74)	30 (16.3)	0.72 (0.29–1.84)
7–14 (secondary)	107 (26.3)	0.84 (0.56–1.27)	22 (20.6)	1.03 (0.42–2.50)
≥15 (higher)	52 (30.4)	1.00	10 (19.2)	1.00
Current smoking	P = 0.01	NS
No	267 (33.4)	1.00	48 (18.0)	1.00
Yes	76 (25.3)	0.63 (0.42–0.94)	P < 0.05	14 (18.4)	1.20 (0.51–2.79)
Current alcohol consumption	NS	NS
No	324 (31.7)	1.00	56 (17.3)	1.00
Yes	19 (24.7)	0.84 (0.47–1.52)	6 (31.6)	2.81 (0.87–9.10)
BMI, kg/m²	P < 0.001	NS
<25	137 (24.8)	1.00	29 (21.2)	1.00
25–29	158 (35.5)	1.52 (1.05–2.18)	P < 0.05	26 (16.5)	0.65 (0.17–2.14)
≥30	48 (47.1)	2.36 (1.32–4.22)	P < 0.01	7 (14.6)	0.60 (0.21–1.95)
Waist circumference, cm	P < 0.001	P < 0.05
Low	117 (24.6)	1.00	28 (23.9)	1.00
Middle	130 (32.4)	1.21 (0.84–1.76)	24 (18.5))	0.57 (0.27–1.22)
High	96 (43.0)	1.51 (0.94–2.43)	10 (10.4)	0.23 (0.07–0.72)	P < 0.05

Data expressed as n (%) of subjects.

Percentages are age-adjusted to Chinese census data for 2000

Adjusted for all other variables in the table.

Pearson’s χ²-test.

OR, odds ratio; CI, 95% confidence interval; BMI, body mass index; NS, not statistically significant (P > 0.05).

Blood pressure was controlled in only 18.1% (n = 62) of the 343 participants receiving medication for their hypertension (Table 2). Hypertension was controlled in 5.6% of all participants with the condition, regardless of treatment status. The rate of BP control was significantly lower in individuals in the high waist circumference group compared with those with a low waist circumference (P < 0.05). Hypertension was less likely to be controlled to <140/90 mmHg in individuals with abdominal obesity (Table 2).

Discussion

This 2010 survey showed that 37% of participants had hypertension, which equates to one in three adults. Only 37% of those participants with hypertension were, however, aware of their condition. Among the subjects aware of their hypertension, 83.8% were receiving antihypertensive medication, although BP was controlled in less than one in five of these individuals and was controlled in only 5.6% of all subjects with hypertension. As previously reported, hypertension prevalence increased significantly with increasing age and BMI.^1,10 Although older or obese participants with hypertension in the present study were more frequently receiving antihypertensive medication, BP control was still poor.

The present study utilized a cross-sectional design, which precludes any inferences about causality. Diagnosis of hypertension was based on three BP measurements on a single day, which could result in misclassification of subjects with white-coat or masked hypertension. As such, it is possible that the prevalence of hypertension could have been overestimated and the rates of awareness, treatment and control correspondingly underestimated. These considerations, however, do not prejudice comparison with previous epidemiological studies that have used similar measurement methodologies.

Prevalence, awareness and treatment of hypertension in Chinese populations have been previously studied as part of the China Hypertensive Survey (CHS, 1991), a nationwide survey of blood pressure and hypertension (2000–2001), and the 2002 CNNHS.^1,17,18 Although the data from these surveys are not directly comparable with the present study due to differences in sampling methods, they suggest that prevalence, awareness and treatment of hypertension are increasing: prevalence of hypertension was 13.6% in 1991, 27.2% in 2000–2001, 18.8% in 2002,^1,17,18 and 36.7% in 2010, as determined by the present study. Awareness of hypertension has, however, improved only a little, from 27% in 1991^{1
7} to 37% in the present study. In contrast, the rates of pharmacological treatment in individuals aware of their condition have almost doubled from 44% in 1991 to 78% in 2002 and 83.7% in 2010. Rates of hypertension control observed in the present study were similar to those reported by the 2002 CNNHS¹ and the 1991 CHS¹⁸ and remain unacceptably low: rates were 8.1% in 1991 and 18.1% in 2010, representing only 5.6% of patients with hypertension overall. Collectively all these data suggest that the prevalence of hypertension is rapidly rising in China and although awareness and treatment have improved to some extent, these remain low, as does control of BP in individuals with hypertension.

The increasing prevalence of hypertension in rural areas, as revealed by the present survey, is a serious health problem.⁶ Figures are close to those reported for some developed countries^10,11 and for northern China,⁶ and are higher than those reported in some developing countries,^12,19 and in southern China.²⁰ Increases in the prevalence of hypertension are probably attributable to lifestyle changes in China over recent years;²¹ in the past two decades, increasing economic development and modernization have caused detrimental changes to diet and lifestyle. These, in turn, have resulted in increases in risk factors for chronic disease such as being overweight or obese.^22,23 In the present study, the number of overweight and obese adults was high, equating to one in three individuals. Being overweight or obese are important predictors of hypertension;²⁴ almost 50% and 77% of subjects with hypertension in the present study were overweight or obese, respectively. It is, therefore, likely that rises in the number of overweight and obese people in the population is a major contributing factor to the increased prevalence of hypertension.²⁴ The present study also provided evidence that participants with lower educational levels are more likely to have hypertension. Poorly educated subjects may have difficulty recognizing the health hazards of poor diet and lifestyles, thus increasing the risk factors for chronic disease. Other risk factors such as higher dietary intake of sodium, high-fat diets and lower levels of physical activity are also associated with the increasing prevalence of hypertension in north-western China.^21,25

Rates of awareness and treatment observed in the present study were 37.0% and 31.2%, respectively. These values are much lower than the rates reported for developed countries^10,13 but similar to data obtained from some developing countries and southern China.^19,20 These data indicate that many of the individuals with hypertension from the present surveillance areas had never had their BP measured and were not aware of their condition. Furthermore, only one third of these subjects were receiving antihypertensive medication. This finding may be partly attributable to the continuing increase in absolute numbers of people with hypertension in China and partly to the fact that the BP of many adults has never been measured due to a lack of knowledge regarding hypertension.⁶ Of subjects who were aware of their condition in the present study, 83.7% were receiving antihypertensive treatment, indicating that an improvement in awareness of hypertension is a key factor in enhancing rates of treatment and control. The high proportion of subjects aware of their hypertension that were receiving treatment may be explained by access to health insurance and the opening of new co-operative medical services in rural areas of China. State reimbursement for antihypertensive prescriptions may also contribute to the observed rates. Data from the present survey also suggested that both increasing age and BMI are associated with greater awareness and treatment of hypertension, and might, therefore, be associated with improved control. It may be that older and obese subjects with hypertension are more concerned about their BP and so are more likely to receive antihypertensive medication than younger subjects and those of normal weight.

The present study found that rates of hypertension control are similar to those observed a decade ago.¹ Rates in the present study and those determined in previous Chinese surveys remain unacceptably low and less than the average rates in both developed (including the USA) and developing countries.^10,11,19,26 Low rates of hypertension control could be explained by a combination of inadequate patient knowledge, lack of understanding of the risks associated with increased BP, poor compliance with prescribed medications, and lack of awareness of the degree of BP control.⁶ The rate of control among patients receiving treatment for hypertension was three-fold higher than the rate in all patients with hypertension in the surveyed population. This indicates that receiving antihypertensive medication is still an important measure for controlling BP. Rates of control did not correlate with age and sex but decreased with increasing BMI although this was not statistically significant. Among treated patients, the rate of hypertension control was lower in those who were overweight and obese compared with those with a normal BMI. This finding suggests that despite overweight and obese patients with treated hypertension paying more attention to their BP, this does not translate into good control. Thus, the present study indicates that control of obesity in general, and abdominal obesity (as determined by waist circumference) in particular, is an important measure for improving BP control rates.

In conclusion, the present study provided evidence that prevalence of hypertension is rapidly increasing in rural areas of north-western China, but that rates of awareness and treatment of hypertension remain low. Furthermore, the BP of individuals with hypertension was found to be poorly controlled. Based on these data, the authors urgently recommend the adoption of measures to improve awareness, treatment and control of hypertension in rural populations in order to improve prevention and management of hypertension.

Footnotes

Acknowledgements

The authors wish to thank the field team from the Centres for Disease Control and Prevention in the study surveillance areas for their contribution to data collection, and the local community health doctors and nurses for providing field work assistants.

Declaration of conflicting interest

The authors declare that there is no conflict of interest.

Funding

Financial and technical resources for this study were provided by the Chinese Government and Chinese Centre for Disease Control and Prevention.

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