Prevalence, awareness, treatment, control and risk factors of hypertension in Korea: the Ansan study

Prevalence, awareness, treatment, control and risk factors of hypertension in Korea: the Ansan study Objectives To determine prevalence, awareness, treatment, and control of hypertension

Prevalence, awareness, treatment, control and risk factors of hypertension in Korea: the Ansan study

Objectives To determine prevalence, awareness,

treatment, and control of hypertension, and its risk factors

in an urban Korean population

Design and setting A cross-sectional survey in Ansan-city,

Korea

Subjects and methods Population-based samples of

people aged 18±92 years in Ansan-city, Korea, were

selected, yielding 2278 men and 1948 women, and their

blood pressures were measured using a highly

standardized protocol Hypertension was de®ned as a

systolic BP > 140 mmHg or diastolic BP > 90 mmHg or

reported treatment with antihypertensive medications, and

subclassi®ed according to 1999 WHO-ISH guidelines

Isolated systolic hypertension (ISH) de®ned as a systolic

BP > 140 mmHg and diastolic BP < 90 mmHg was also

examined Data were strati®ed by age and sex

Results The overall prevalence of hypertension in this

study was 33.7% Among these, 64.9% had Grade 1

hypertension, 22.5% Grade 2, and 12.5% Grade 3

Age-speci®c prevalence of hypertension increased

progressively with age, from 14.19% in 18 to 24 year-olds

to 71.39% in those 75 years or older Hypertension

prevalence was signi®cantly higher in men (41.5%) than in

women (24.5%) (P < 0.001) Isolated systolic hypertension

had signi®cantly lower prevalence (4.33%) within the

population, although in the elderly aged 55 years or more it

rose by 11.13% Overall, 24.6% of hypertensive individuals

were aware that they had high blood pressure, as much as

78.6% were being treated with antihypertensive

medications, and 24.3% were under control Hypertension awareness as well as treatment and control rates varied by sex, with women higher in all three rates Multivariate analysis revealed that age, body mass index and abdomen circumference were signi®cantly associated with

prevalence of hypertension both in men and women Conclusions Hypertension is highly prevalent in Korea Despite the high rate of treatment, the rates of awareness and control are relatively low, suggesting the nationwide demand for preventing and controlling high blood pressure

in Korea in order to avert an epidemic of cardiovascular disease J Hypertens 19:1523±1532 & 2001 Lippincott Williams & Wilkins

Journal of Hypertension 2001, 19:1523±1532 Keywords: awareness, control, hypertension, Korea, prevalence, risk factor, treatment

a Division of Cardiovascular Research, Department of Biomedical Sciences, National Institute of Health, Seoul, Korea, b Ansan Health Center, Korea University Hospital, Ansan-city, Kyonggi-do, Korea, c College of Nursing Science, Ewha Womans University, Seoul, Korea, and d Division of Endocrinology and Metabolism, Department of Internal Medicine, College of Medicine, Seoul National University, Seoul, Korea.

Sponsorship: This work was supported in part by National Institute of Health, Korea grant no 334±6113±211±207±00 (I.J.) and by Korea University Institutes of Medical Science grant 2000±n6 (C.S.).

Correspondence and requests for reprints to Chol Shin, M.D F.C.C.P., Ph.D Ansan Health Center, Korea University Hospital, 516 Gojan-dong, Ansan-city, Kyonggi-do, (425±707), Korea.

Tel: ‡82 31 412 5602; fax: ‡82 31 412 5604; email: chol-shin@hanmail.net Received 28 December 2000 Revised 16 March 2001

Accepted 11 April 2001

Introduction

The improved control of infectious and parasitic

dis-eases and the sharp decrease in infant mortality during

recent decades have dramatically changed the health

pro®le of many developing countries [1] This is

re¯ected in an increase in life expectancy and the

emergence of cardiovascular diseases (CVD) as a

lead-ing cause of morbidity and mortality in such countries

[2] In fact, CVD including stroke are still the leading

cause of all death in Korea [3], which accounted for

23.3% in 1999, although in 1983 it was responsible for

as high as 27.8% of nation's mortality

Recognizing the rapid emergence of CVD as a clinical

and public concern in Korea, the nationwide Korea Health and Nutrition Survey was initiated in 1998 to assess the prevalence of selected life-style-related dis-eases and their risk factors including hypertension No of®cial results from Korea Health and Nutrition Survey have been, however, published to date

High blood pressure (BP) is one of the most important risk factors for CVD, and it has been shown that the reduction of highly or moderately elevated BP levels results in a decrease in stroke and myocardial infarction rates [4,5] One of the cornerstones of the primary prevention of CVD since the early 1970s has focused

on screening and early antihypertensive drug treatment

0263-6352 & 2001 Lippincott Williams & Wilkins

of subjects presenting high BP [6] Although

commu-nity-based or national programs for detection and

treat-ment of hypertension have been carried out in many

countries [7±14], only a few studies of hypertension

prevalence have been done in Korea [15±17]

Further-more, these studies were con®ned to analyses from 8 to

10-year-old surveys In order to better assess the

current status of hypertension screening and

manage-ment, we recorded measurements of hypertension

pre-valence, awareness, treatment and control in a

randomized Korean population

Materials and methods

Subjects

The study area from which the participants were

recruited is situated in a southwestern part of Seoul

named Ansan-city, Kyonggi-do in South Korea, and is

characterized by a newly industrializing town from a

farming county The city comprises 250 000 population

aged more than 18 years The target study sample was

4700 subjects aged more than 18 years who were

randomly selected based upon address codes from June

1999 to April 2000 All were visited and interviewed by

well-trained nursing students A total of 427 subjects

(9.09%) refused to participate in the survey

Further-more, we failed to collect suf®cient information

regard-ing a detailed history and examination from 47 other

subjects Complete data for the analysis of hypertension

and possible risk factors in this study were, therefore,

available and based on the remaining 4226 subjects

(2278 men, 1948 women)

Questionnaires and blood pressure measurement

The survey team consisting of nursing students was

well trained in the details of questionnaires and

meas-urements before starting the survey In particular, all

the surveyors were encouraged to read BP readings

within a 2 unit error on their sequential measurements

during practice A team of two surveyors visited each

home and interviewed the volunteer subjects Only one

person aged more than 18 years within the households

was asked to participate in an interview While one

surveyor interviewed the study subject, the other asked

another individual within the household for

con®rma-tion of the data Detailed informacon®rma-tion included sex,

weight (portable scales: SECA, Hamburg, Germany;

calibration monthly), height (steel ruler), abdomen

circumference, alcohol intake, smoking, household

in-come, occupation, marital status, years of education,

driving, and BP BP was measured according to World

Health Organization-International Society of

Hyper-tension (WHO-ISH) guidelines [18] using

Bauman-ometer1 (WA Baum Co Inc Copiague, New York,

USA) Three BP readings were taken on either arm

with 5 min intervals Subjects were seated and caffeine

substances and smoking were restricted for 30 min

before the measurement Data presented here are the average of three measurements

De®nitions

Hypertension was de®ned as a systolic BP >

140 mmHg or diastolic BP > 90 mmHg according to WHO-ISH criteria [18] or a subject's currently receiv-ing antihypertensive treatments to control hyper-tension, regardless of the measured level We further classi®ed the severity of hypertension as normal (systo-lic BP , 140 mmHg and diasto(systo-lic BP , 90 mmHg), Grade 1 (140±159 for systolic BP/90±99 mmHg for diastolic BP), Grade 2 (160±179/100±109 mmHg), and Grade 3 (> 180/110 mmHg) Isolated systolic hyper-tension (ISH) was de®ned as a systolic BP >

140 mmHg and diastolic BP , 90 mmHg Body mass index (BMI) was calculated from the simple equation (body weight in kg divided by height in m2) Smoking was classi®ed as current, ex- (not for at least 1 year), and non-smoker Alcohol intake was classi®ed as drin-ker and non-drindrin-ker from self-administered question-naire Awareness of hypertension was de®ned as a subject who reported a history of previous diagnosis of hypertension or high BP Treatment of hypertension was de®ned as a subject who currently uses prescribed antihypertensive drugs Control of hypertension was de®ned as a subject who was receiving treatment for hypertension and kept BP normal (systolic

BP , 140 mmHg and diastolic BP , 90 mmHg)

Data analysis

All the data of this study were summarized as mean and standard deviation for continuous variables and as frequency and percentage for categorical variables Intergroup comparison for risk factors among subjects with or without hypertension was performed using a ÷2

test for distribution and t-test for continuous variables The signi®cance of various risk factors was calculated

by logistical regression analysis where the odds ratio and 95% con®dence intervals (CI) were calculated using multivariate analysis All the analyses were con-ducted using the statistical software package SAS V6.12 [19] and a probability value of P , 0.05 was considered

to be signi®cant

Results

General characteristics

The mean age of the study participants was 45.3  17.9 (mean  SD) years (range 18±92 years) The mean age (46.5  17.2) of the men was slightly, but statistically signi®cantly higher than that (44  18.6) of the women All anthropometric data tested in this study was sig-ni®cantly higher in men than in women A total of 21%

of the population had attended at least high school Generally, men had higher education levels than wo-men The majority had a partner (75.1% of the men and 65.7% of the women) and occupation (77.9% of the

men and 74.2% of the women) Other detailed life style

characteristics for the study population are shown in

Table 1

Blood pressure

BP distributions were approximately Gaussian, with a

rightward skew (Fig 1) Mean systolic and diastolic BP

(mmHg) was 128.9  18.0 and 83.6  12.9 for men; and

121.1  18.1 and 77.3  12.6 for women, respectively

(Table 1) Figure 2 displays the mean systolic and

diastolic BP by age and sex Mean systolic BP rose

progressively across entire age range The slope of the

rise in systolic BP was bigger in women than in men

Although systolic BP in women was signi®cantly lower

before the age of 54 (P , 0.01), it appeared that there

was no signi®cant difference between 55 and 74 years

of age (P 0.05), and even a reversal was noted after

75 (P , 0.05) The pattern for mean diastolic BP was

similar at a younger age (before the age of 45), but the

average level of diastolic BP plateaued in men after the

age of 45 and in women after the age of 55,

respec-tively Mean diastolic BP was almost the same in both

men and women after the age of 55 years

Prevalence of hypertension

Table 2 presents the speci®c and

age±sex-adjusted prevalence of hypertension Overall, 33.7% of

all studied population were hypertensive Hypertension

appeared to be signi®cantly more common in Korean men (41.53%) than women (24.54%) (P , 0.001) Hypertension prevalence increased progressively with age In the youngest age group (18±24 years) hyper-tension was present in 14.19% of the population, whereas the prevalence rate was 71.39% in the oldest age group (75±92 years) National estimates of the hypertension prevalence were calculated using the available census data in 1995 [20], resulting in 35.8, 21.6 and 28.6% in age-adjusted men, women, and age± sex-adjusted total population of Korea, respectively (Table 2) Using subclassi®cation of BP according to WHO-ISH guidelines, 64.9% of hypertensive popu-lation excluding antihypertensive drug takers had Grade 1 BP; 22.5% Grade 2, 12.5% Grade 3, as shown

in Table 3 Hypertension severity varied signi®cantly until the age of 54, showing increases in both Grade 2 and 3 BPs compared with decrease in Grade 1 BP After the age of 55, however, the prevalence of each Grade BP remained relatively constant Grade 1 BP reading was most prevalent (89.1%) between the age of 18±24 years No signi®cant difference was found in the severity of sex-speci®c hypertension Table 4 shows the age- and sex-speci®c prevalence of ISH The overall prevalence of ISH in the studied population was 4.33%, and it signi®cantly (P , 0.001) increased with age Furthermore, the prevalence of ISH rose signi®cantly from 1.36% in all population aged 18±54 years to

Men (n ˆ 2278) Women (n ˆ 1948) All (n ˆ 4226)

Mean  SD Age (years), y 46.5  17.2 44.0  18.6 45.3  17.9 SBP (mmHg) 128.9  18.0 121.1  18.1 125.3  18.4 DBP (mmHg) 83.6  12.9 77.3  12.6 80.7  13.1 Height (cm) 169.3  6.1 157.3  6.4 163.8  8.6 Weight (kg) 66.2  9.3 55.0  8.2 61.0  10.4 Abdomen circumference (cm) 86.9  10.6 82.2  13.4 84.7  12.2 BMI (kg/m 2 ) 23.1  2.8 22.3  3.3 22.7  3.1

Number of subjects (%) Years of education (%)

< 12 years 1650 (72.4) 1673 (85.9) 3323 (78.6)

Marital status (%)

Occupation (%)

Household income (US$/month) (%)

Alcohol intake (%)

Smoking status (%)

Current smoker 1308 (57.5) 116 (2.7) 1424 (33.7)

SBP, systolic blood pressure; DBP, diastolic blood pressure; BMI, body mass index y Means of variables were signi®cantly different between men and women,  P , 0.001 Distributions of subjects were signi®cantly different among variable categories and between gender,  P , 0.05.

11.13% in those aged 55±92 years In the elderly (after the age of 55), the prevalence of ISH in men and women was 10.56 and 11.92%, respectively, showing that ISH appeared to be more common in women than

in men in this age group, however, no gender differ-ence in the prevaldiffer-ence of ISH was found (P ˆ 0.512)

Hypertension awareness, treatment, and control

Table 5 showed that approximately a quarter (24.6%)

of the studied population who could be classi®ed as hypertensive, were aware of their high BP Rates of awareness were higher in women (33.5%) than men (20.1%) (P , 0.001) The estimated percentage of hypertensive individuals receiving pharmacological treatment in Korea was 78.6% A higher proportion of women (85.0%) were being treated than men (73.2%) (P , 0.01) The estimated percentage of hypertensive individuals whose BPs were under control (systolic

BP , 140 mmHg and diastolic BP , 90 mmHg) was 24.3% Better control rates were noted in women (27.9%) than men (20.9%), but no signi®cant difference was found (P ˆ 0.354)

Risk factors associated with hypertension

The demographic, anthropometric and lifestyle charac-teristics of subjects with or without hypertension were presented in Table 6 The prevalence of hypertension

in both genders was associated with greater age (P , 0.001) Hypertension was also signi®cantly asso-ciated with higher body mass index (BMI), greater abdomen circumference, years of education, marital status, occupation, driving, smoking, and lower house-hold income in both genders Alcohol intake was associated with hypertension in women (P , 0.01), but not in men When age-adjusted, BMI and abdomen circumference in men had a strong dose±response relationship over their entire ranges as shown in Table

7 In women, however, these relationships were only true at BMI > 26 kg/m2 and abdomen circumference

95 cm Hypertension was signi®cantly less prevalent in those who earned the highest incomes in both genders (P , 0.01) Interestingly, alcohol intake was associated

Fig 1

Bar graphs showing distribution of (a) systolic and (b) diastolic blood

pressures in the Ansan adult population.

0

200

400

600

800

1000

1200

,60

60 270280 29021001102 1202 1302 1402 1502 1602 1702 1802 1902 2002 2

SBP (mmHg) (a)

0

200

400

600

800

1000

1200

1400

1600

,40

40 250260 270280 2902100 21102120 21302140 2

DBP (mmHg) (b)

50

70

90

110

130

150

18–24 25–34 35–44 45–54 55–64 65–74 75–92

Age group (years)

c

c

bc c

b c

a b

a a

a a

a a

d

d

d

d

d

d

c c

b b

a a

a a

*

Fig 2

Line graph shows systolic blood pressure (SBP) and diastolic blood

pressure (DBP) by age and sex (M, male; F, female) among the Ansan

adult population Different letters means signi®cantly different group at

P ˆ 0.0001 by analysis of variance (ANOVA) test.P , 0.01;

 P , 0.001) in SBP and DBP between men and women of same

age group.

Crude prevalence, y 41.5 24.5 33.7 National estimate 35.8 21.6 28.6 §

Hypertension, diastolic blood pressure > 90 mmHg or systolic blood pressure > 140 mmHg y Crude prevalence was signi®cantly different between men and women,  P , 0.001 § Age-sex-adjusted hypertension prevalence by the total population of Korea in 1995.

with hypertension only in men, not in women, after age

adjustment (Table 7) In comparison, as shown in

Table 6, a signi®cant relationship with alcohol was

observed only in women, not in men, without age

adjustment No signi®cant relationships with all other

lifestyles were observed in both genders after age

adjustment (Table 7) Multivariate logistic regression

analysis showed that regardless of age and sex, in men,

age, BMI, abdomen circumference and alcohol intake

were independent risk factors and showed strong

association with hypertension (Table 8) In women,

however, alcohol intake lost its signi®cance Only weak,

but still signi®cant association was observed with BMI

in women (P ˆ 0.07) No independent associations with hypertension were found with years of education, occupation, household income and smoking in both genders

Discussion

Our results showed that the overall prevalence of hypertension, estimated to be 33.7%, exceeds those of many countries [8,21±24] This is especially noteworthy because this study included a comparatively younger ( > 18 years old) age group than other studies In many

(WHO-ISH) criteria (%)

Severity

Grade 1 (mild) 57 (89.1) 121 (76.1) 168 (70.0) 89 (58.9) 95 (59.4) 127 (58.3) 89 (56.7) 46 (64.9) Grade 2 (moderate) 6 (9.4) 26 (16.4) 45 (18.8) 39 (25.8) 41 (25.6) 58 (26.6) 44 (28.0) 259 (22.5) Grade 3 (severe) 1 (1.6) 12 (7.5) 27 (11.3) 23 (15.2) 24 (15.0) 33 (15.1) 24 (15.3) 144 (12.5)

Grade 1 (mild) 41 (85.4) 100 (75.8) 130 (68.1) 63 (56.8) 74 (60.7) 78 (56.1) 38 (59.4) 524 (64.9) Grade 2 (moderate) 6 (12.5) 22 (16.4) 36 (18.8) 27 (24.3) 31 (25.4) 40 (28.8) 15 (23.4) 177 (21.9) Grade 3 (severe) 1 (2.1) 10 (7.6) 25 (13.1) 21 (18.9) 17 (13.9) 21 (15.1) 11 (17.2) 106 (13.1)

Grade 1 (mild) 16 (100) 21 (77.8) 38 (77.6) 26 (65.0) 21 (55.3) 49 (62.0) 51 (54.8) 222 (64.9) Grade 2 (moderate) 0 4 (14.8) 9 (18.4) 12 (30.0) 10 (26.3) 18 (22.8) 29 (31.2) 82 (24.0) Grade 3 (severe) 0 2 (7.4) 2 (4.0) 2 (5.0) 7 (18.4) 12 (15.2) 13 (14.0) 38 (11.1)

Grade 1 blood pressure (BP) indicates 140±159 mmHg systolic blood pressure (SBP) or 90±99 mmHg diastolic blood pressure (DBP); Grade 2, 160±179 mmHg SBP or 100±109 mmHg DBP; Grade 3, > 180 mmHg SBP or > 110 mmHg DBP P , 0.001 for all differences y Excludes those reporting treatment with

antihypertensive drugs.

Isolated systolic hypertension (ISH), diastolic blood pressure (DBP) , 90 mmHg and SBP > 140 mmHg y No gender difference in the

prevalence of ISH was found in population aged more than 55 years (P ˆ 0.512) § Crude prevalence was different between men and

women, but not signi®cant (P , 0.051).

Prevalence 946/2278 (41.5%) 478/1948 (24.5%) 1424/4226 (33.7%) , 0.001 Awareness 190/946 (20.1%) 160/478 (33.5%) 350/1424 (24.6%) , 0.001 Treatment 139/190 (73.2%) 136/160 (85.0%) 275/350 (78.6%) , 0.01 Control 29/139 (20.9%) 38/136 (27.9%) 67/275 (24.3%) NS Awareness, the number of hypertensive persons who were diagnosed before; Treatment, the number of hypertensive persons who uses anti-hypertension drugs; Control, the number of persons who keep blood pressure normal (diastolic blood pressure , 90 mmHg and systolic blood pressure , 140 mmHg) among treatments NS, not signi®cant (P ˆ 0.354).

other countries, however, the prevalence of

hyper-tension was also reported to be higher than that in the

present data [25±27] These differences may re¯ect the

effects of dynamic interactions between genetic,

socio-cultural, demographic and economic factors From this

point of view, each country's own data should be of

great importance to later develop a hypertension

sur-veillance system at the global level The prevalence of

hypertension shown in this study was comparable to

those from National Health and Nutrition Examination

Survey (NHANES) I [7], western India [9], and

south-eastern Spain [28] In Korea, however, earlier surveys

reported signi®cantly lower prevalence [15±17],

sug-gesting an upward trend in the prevalence of

hyper-tension for 1990±1992 in Korea A similar trend was

observed in the prevalence of hypertension in China during 1980±1991 [23] In comparison, a signi®cant downward trend in mean systolic BP and in the prevalence of hypertension was detected in US [7] during 1960±1991 and Finland [26] during 1982±1997 The differences in trends among these are of great importance, but yet to be fully understood One possible explanation is that highly developed countries have already provided good surveillance systems to control and prevent high BP, while Korea is only currently initiating one

An interesting ®nding of the present study is that the prevalence of hypertension in men is signi®cantly (P , 0.001) higher than in women, as shown in Table

Hypertensive Normotensive Hypertensive Normotensive Risk factors (n ˆ 946) (n ˆ 1332) (n ˆ 478) (n ˆ 1470)

Age (years) 51.7  17.4 42.8  16.1 62.2  17.6 38.1  14.6

Age group

BMI (kg/m 2 ) 23.8  2.86 22.6  2.72 23.5  3.72 21.9  3.05

BMI group

Abdomen circumference (cm) 90.6  8.78 84.9  8.40 91.1  11.9 80.1  10.2

Years of education y

Marital status

Occupation

Driving

Alcohol intakeé6

Smoking status

Household income (US$/

month)

Distributions of hypertensives and normotensives in both genders were signi®cantly different (P , 0.001) by all variables except

years of education and alcohol intake y Men, P , 0.05; women, P , 0.01 § Men, not signi®cant; women, P , 0.01.

2, which contributed to high overall prevalence It is

interesting, but not totally new, since Jee et al [16] have

already reported that the prevalence of hypertension

was 28.9% in Korean men and 15.9% in Korean women

Furthermore, an interesting result when working on a

Bulgarian population study, showed a signi®cantly

high-er prevalence of age-adjusted hyphigh-ertension in men

(59.1%) than that in women (36.2%) (P , 0.001) [14]

The reasons for these large gender differences resulting

from the present study have not been determined with

certainty to date One possible explanation is that the

men had a higher BMI and greater abdomen

circumfer-ence as shown in Table 1, which can contribute to

higher prevalence of hypertension Despite the signi®-cant gender difference of overall hypertension preva-lence, the general pattern of an increasing average systolic BP has been recognized as in previous studies (Fig 2) [8,14] Also, the pattern of the age-related increase in diastolic BP followed by a plateau from middle-age has been the norm in most surveys, [14] The prevalence of hypertension classi®ed by severity was dramatically changed by age (Table 3) For exam-ple, between 65 and 74 years of age, 56.1% of men had Grade 1; 28.8% Grade 2; 15.1% Grade 3, whereas 62.0% of women had Grade 1; 22.8% Grade 2; 15.2%

Risk factors Odds ratio (CI) odds ratio (CI)Age-adjusted Odds ratio (CI) Age-adjusted oddsratio (CI)

Age (years)

BMI (kg/m)

20±22 1.31 (0.96±1.78) 1.61 (1.16±2.23) 1.23 (0.89±1.70) 1.12 (0.75±1.66)

22±24 1.87 (1.38±2.52) 2.15 (1.57±2.95) 1.75 (1.27±2.41) 1.38 (0.94±2.03)

24±26 2.42 (1.78±3.30) 2.75 (1.99±3.80) 2.23 (1.56±3.20) 1.26 (0.82±1.94)

26±28 4.27 (2.93±6.22) 4.98 (3.37±7.37) 3.85 (2.53±5.84) 1.87 (1.13±3.09)

> 28 4.64 (2.92±7.40) 5.32 (3.28±8.61) 5.60 (3.62±8.67) 2.35 (1.40±3.92) Abdomen circumference (cm)

75±80 1.86 (1.22±2.84) 1.62 (1.05±2.49) 2.13 (1.40±3.26) 1.37 (0.86±2.17)

80±85 2.24 (1.51±3.32) 1.80 (1.20±2.68) 3.18 (2.13±4.74) 1.52 (0.97±2.37)

85±90 2.84 (1.93±4.19) 2.14 (1.44±3.19) 3.99 (2.68±5.94) 1.12 (0.70±1.78)

90±95 5.84 (3.94±8.67) 4.04 (2.69±6.08) 6.27 (4.12±9.55) 1.51 (0.92±2.47)

95±100 7.39 (4.83±11.3) 5.01 (3.23±7.77) 14.8 (9.50±23.1) 2.72 (1.61±4.59) 100 10.6 (6.62±17.0) 6.90 (4.24±11.2) 21.3 (13.7±33.2) 3.12 (1.85±5.28) Years of education

12 years 0.76 (0.63±0.92) 1.02 (0.83±1.24) 0.28 (0.19±0.43) 0.82 (0.52±1.30)

Marital status

Couple 0.66 (0.54±0.80) 0.98 (0.79±1.22) 2.39 (1.94±2.95) 1.24 (0.93±1.64)

Occupation

Without 1.94 (1.56±2.33) 1.00 (0.79±1.28) 9.28 (7.34±11.7) 1.56 (1.08±2.25)

Driving

No 1.58 (1.33±1.88) 1.01 (0.83± 1.23) 3.17 (2.27±4.44) 1.31 (0.90±1.90)

Household income ($US/month)

850±1700 0.39 (0.31±0.49) 0.85 (0.63±1.14) 0.39 (0.31±0.49) 0.84 (0.63±1.14)

1700±2550 0.24 (1.71±0.34) 0.92 (0.62±1.38) 0.24 (0.17±0.34) 0.91 (0.61±1.36)

> 2550 0.11 (0.06±0.20) 0.42 (0.21±0.82) 0.11 (0.06±0.20) 0.41 (0.21±0.81)

Alcohol intake

Yes 1.09 (0.92±1.30) 1.34 (1.11±1.61) 0.52 (0.41±0.67) 1.23 (0.92±1.66)

Smoking status

Current smoker 0.94 (0.77±1.14) 0.96 (0.78±1.18) 1.98 (1.34±2.92) 0.98 (0.59±1.62)

Ex-smoker 1.37 (0.06±1.78) 1.05 (0.80±1.39) 1.47 (0.51±4.25) 0.44 (0.12±1.52)

CI, con®dence interval; BMI, body mass index §,  P , 0.05, P , 0.01, P , 0.001.

Grade 3 To what extent well-established risk factors

for hypertension, such as BMI, years of education,

occupation, alcohol intake and smoking, account for the

observed age-speci®c variation in hypertension severity

is an important issue worthy of further investigation

As shown in Table 4, ISH was not common (1.36%) in

the population aged , 54 years, while its prevalence

greatly increased (11.13%) in the elderly ( 55 years)

This result supported again that ISH is the most

common form of hypertension in the elderly [29,30]

The prevalence of ISH in the elderly Korean could not

be directly compared with other previous ®ndings,

since each study employed different de®nitions

(diasto-lic and systo(diasto-lic cut-off points) and age distribution of

the population studied Several other factors besides

de®nitions and age group studied were gender, social

class, the number of blood pressure readings performed,

geographical location, and treatment status [30,31]

Because of these limitations, the prevalence of ISH

varied from study to study; ranged from 1% in Israel to

24% in Norway when the criterion of ISH de®ned as a

systolic BP > 160 mmHg and diastolic BP , 90 or

95 mmHg was used [31] When the lowest limit of

systolic BP was adjusted as 140 mmHg, the prevalence

of ISH in the elderly Korean was comparable to that

from the 1992±1993 Mexican study [32] Furthermore,

it was also found to be signi®cantly lower than those in

the studies by Multiple Risk Factor Intervention Trial

Research Group [33], Psaty et al [34], and Kocemba et

al [35] Despite signi®cantly lower prevalence from

this study, however, it is likely that ISH will become a

truly major medical and social problem since

popula-tions in Korea are becoming older Insigni®cant or less

gender difference in the prevalence of ISH in the

elderly Korean may re¯ect the fact that ISH is primarily

a characteristic of older ages at a time when the male

and female systolic pressure difference is minimal or

reversed [36]

Although 33.7% of the total population were hyper-tensive, only one-quarter (24.6%) of hypertensive in-dividuals were aware of their condition (Table 5) This low rate of awareness is somewhat unexpected, since Korean National Health Insurance Policy has provided most Koreans with medical examinations including BP measurement, every other year This suggested, in part, delinquent measurement of hypertension during exam-ination As much as 65% awareness was reported from the population-based study in Barbados [37] A recent study in Austria advised improved strategies to achieve better community control of hypertension since they found that the intensive blood pressure education campaign had only a temporary effect on improving blood pressure awareness [38]

Despite the low rate of awareness in Korea, the diag-nosis of hypertension led to medical treatment in about three-quarters (78.6%) of patients This is not surpris-ing, since hypertensive patients were within easy access

of inexpensive antihypertensive medication in Korea Contrary to treatment, the control of hypertension by antihypertensive drug therapy was rather low, with only one-quarter (24.3%) of treated patients achieving an adequate BP control One possible explanation might

be a lack of aggressiveness in treating the patients [39] Another accepted reason for not achieving goal BP is poor patient compliance with the antihypertensive medication According to many studies, only 50±60% of patients adhere well to the prescribed medication [40,41] It has been suggested that interventions fo-cused on better patient compliance should be persona-lized and multifactorial, but no detailed studies are so far available [42] The other possible reason may be the side-effects of the antihypertensive drugs currently available The low ef®cacy of antihypertensive treat-ment in the community raises an important question of its cost-effectiveness Indeed, an ineffective treatment will greatly increase the costs induced by the diseases related to hypertension (stroke and coronary heart diseases) The impact on health expenditure of the failure to adequately control BP by drug treatment should thus be considerable

A signi®cantly higher rate of awareness, treatment and control was prominent in women as shown in Table 5 Since men usually could afford to have systematic clinical examinations, it was assumed that the levels of hypertension awareness, treatment and control rates were relatively higher in men than in women Interest-ingly, however, the results from the present study showed that women achieved better awareness, treat-ment and control than men The reason for this result

is yet to be fully understood Another interesting ®nd-ing in the present study is the signi®cant deviation from classical `rule of halves', which is currently con-troversial, to be applied [43]

various risk factors with prevalence of hypertension in Ansan-city,

Korea

Odds ratio (CI) Odds ratio (CI) Age 1.26 (1.17±1.37) ,§ 1.81 (1.62±2.03)

BMI 1.18 (1.08±1.30) 1.09 (0.98±1.21)

Abdomen

circumference 1.27 (1.17±1.37) 1.13 (1.03±1.23)

Years of education 0.97 (0.78±1.21) 0.97 (0.61±1.55)

Marital status 1.16 (0.90±1.48) 1.15 (0.84±1.58)

Occupation 1.08 (0.84±1.48) 1.34 (0.89±2.01)

Household income 1.02 (0.91±1.13) 0.88 (0.74±1.03)

Driving 1.20 (0.96±1.50) 1.16 (0.79±1.70)

Alcohol intake 1.32 (1.08±1.61) 1.23 (0.91±1.66)

Smoking status 0.94 (0.85±1.05) 0.98 (0.76±1.26)

CI, con®dence interval; BMI, body mass index §,  P , 0.05, P , 0.01,

 P , 0.001.

Studies from developing and developed countries have

shown that obesity [9,44±46], smoking [9,46], alcohol

intake [18,46], and years of education [47±49] are

associated with the prevalence of hypertension The

present data are in accord with an association of

smoking, obesity and less years of education with

hypertension in both genders, but an association of

alcohol intake only in women (Table 6) However,

age-adjustment nulli®ed the signi®cant associations of years

of education, marital status, driving, and smoking with

hypertension (Table 7) It is dif®cult to understand

why our data showed no signi®cant association between

smoking and age-adjusted hypertension in both

gen-ders Since smoking, a well-known risk factor for

hyper-tension [9,46], is relatively popular in Korea, more

detailed studies should be awaited for con®rmation of

this data Both non-working women and alcohol

con-suming males had signi®cant positive associations with

age-adjusted hypertension in this study (P , 0.01) The

signi®cant, but negative association of highest

house-hold income (> US$2550/month) with age-adjusted

prevalence of hypertension in both genders re¯ects that

individuals from high socio-economic status are likely

to prevent or control hypertension This ®nding is

consistent with observations made in developed

coun-tries [50,51] The association of diabetes mellitus with

hypertension is well known [46], and should be

consid-ered as a risk factor in the study However, only 14

individuals from the study population (n ˆ 4226)

re-ported their history in self-administered questionnaires,

and therefore may be considerably underdetected

Therefore we did not analyse this variable in the

current study Obese persons are prone to develop

hypertension and the present data showing the strong

dose±response relationship between BMI and

hyper-tension con®rm this association Average BMI index

(23.8 kg/m2 for men; 23.5 kg/m2 for women) observed

in hypertensives in the present study is usually

consid-ered within desirable limits in developed countries

[52], therefore, lifestyle guidelines for the hypertension

prevention in Korea should be different from those

developed countries The limit of BMI index (22.6 kg/

m2 for men; 21.9 kg/m2 for women) observed in

normo-tensives in this study may be given due consideration

to de®ne safe limits for the risk factor for the

preven-tion of hypertension in Korean Although many risk

factors are to be considered, our data clearly indicated

that BMI and abdomen circumference are independent

and preventable predictors of hypertension in Koreans,

although slightly less signi®cant in women (Table 8)

Therefore, it is widely recognized that the future

programmes for the primary prevention of hypertension

should concentrate on obesity in Korea

In summary, the results from the present Ansan study

show a higher prevalence of hypertension than has

been reported in previous Korean studies Our ®ndings

also suggest strong associations between hypertension and BMI and abdomen circumference There was no signi®cant relationship between hypertension and smoking and this remains to be further studied The extremely high prevalence of hypertension coupled with the disturbingly low prevalence rates of awareness and control has important implications for health care providers, public health of®cials, and health policy-makers in Korea This study identi®es an urgent need for nationwide efforts to prevent and control hyper-tension, in order to avert an epidemic of BP-related atherosclerotic cardiovascular diseases

Acknowledgements

We thank Drs Namhan Cho and Sangmee Ahn Jo for their critical readings, Ms Sun Mi Lee for project coordination, and Ms Jooyoung Lee for secretarial assistance The opinions expressed in this article are those of the authors and do not necessarily imply endorsement by his or her employer or the funding agency

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