Abstract
Objective. Control of blood pressure is important in old age for prevention of hypertension-associated complications. This study aimed to investigate the factors associated with control of hypertension in elderly people (≥60 years old) diagnosed with hypertension. Methods. The subjects were those who had a self-reported diagnosis of hypertension (532 men and 1078 women) from a stratified random cluster sample of 4201 people aged 60 years or older. Controlled hypertension was defined as a systolic blood pressure (SBP) <140 mmHg and diastolic blood pressure (DBP) <90 mmHg, and SBP <130 mmHg and DBP <80 mmHg for subjects with diabetes. Results. The prevalence of controlled hypertension (25.9%) was low. In older women, the prevalence of isolated uncontrolled SBP was increased. After adjusting for other covariates, uncontrolled hypertension was positively associated with body mass index (BMI≥23 kg/m2), and negatively associated with balanced diet and a past history of cardiovascular disease in men, whereas in women it was positively associated with waist circumference (≥80 cm). Conclusions. In elderly people diagnosed with hypertension general obesity (high BMI) appears to have an important influence on uncontrolled hypertension in men, whereas abdominal obesity (high waist circumference) appears to be an important factor in women.
Key Words::
Introduction
Cardiovascular diseases (CVDs) resulting from uncontrolled hypertension are still the leading cause of death (23.0% of total deaths) in South Korea (Citation1). The prevalence of hypertension increases markedly with age in the over-60 age group (Citation2). As the proportion of elderly people in the population increases, the management of uncontrolled hypertension is becoming important because its complications are the major risk factor for CVDs, especially in old age (Citation3). In an area of Korea in which the proportion of old people is large, control of blood pressure should be an important consideration in public health policies.
According to JNC 7 (the Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of High Blood Pressure), mortality from CVD is decreased by appropriate hypertension prevention and management (Citation4). In Korea, control of hypertension also becomes important because only about 20% of all hypertensive persons have been treated (Citation5). For example, the rate of hypertension control was reported as 20.9% in some areas (Citation6). This means that further public health policy should be developed to control hypertension, and a nationwide investigation is needed to determine how well hypertension is controlled.
The rate of control of blood pressure has also been reported to differ between men and women (Citation7), as do the risk factors for hypertension (Citation6). In one study, risk factors for hypertension in women were identified as age and abdominal obesity, while those for men were age, body mass index (BMI), abdominal obesity and alcohol intake (Citation6). Another study showed that women are at higher risk for CVD (Citation8), and it has been shown that some of the risk factors for heart disease in women might be different from those in men (Citation9). Thus, an important component of hypertension control is managing risk factors based on sex.
However, regional surveys to evaluate factors associated with control of hypertension, especially in elderly Koreans, have not been systematically performed. Therefore, this study was conducted to analyze the anthropometric, lifestyle and biochemical characteristics and the factors associated with blood pressure control, all by sex.
Methods
Study population
These analyses were based on the information obtained from participants in the Chungju Metabolic Disease Cohort Study (CMC study) (Citation10,Citation11), an ongoing prospective cohort study that started in 2003. This study was approved by the Institutional Review Board of the Catholic University of Korea.
Subjects were selected by stratified random cluster sampling during 2005 and 2006 of persons aged 40 years or older in Chungju, South Korea. The study area was stratified by the residential areas of 13 health sub-centers and 16 community health clinics. Among people ≥40 years old who participated in the study (n=6388), The subjects were those who had a self-reported diagnosis of hypertension (532 men and 1078 women) from a stratified random cluster sample of 4201 people aged 60 years or older.
All participants gave informed consent. Diagnosis was defined as self-reported diagnosis. Self-reported diagnosis of hypertension was based on the results of a questionnaire in which participants were asked if they had ever been diagnosed with hypertension at a clinic.
Measurements
All the measurements were performed by trained investigators in the morning. Blood pressure was measured on a subject's right arm with the subject in the sitting position after 5 min of rest using World Health Organization-International Society of Hypertension guidelines (Citation12). The subjects were instructed not to smoke or ingest caffeinated beverages 30 min prior to the measurements. Cuff sizes were adjusted to arm circumference and blood pressure measurements were taken on one occasion using a standard mercury Baumomanometer (W.A. Baum, NY). Two measurements were taken in sitting position 2 min apart, and the average of the two measurements was used. Waist circumference was measured using a measuring tape placed in a horizontal plane midway between the lower border of the ribs and the upper margin of the iliac crest. According to WHO data on abdominal obesity in the Asia-Pacific Region (Citation13), abdominal obesity was defined as a waist circumference of 90 cm or greater for men or 80 cm or greater for women. This cutoff for abdominal obesity was also applied to define metabolic syndrome according to the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults, Adult Treatment Panel III (NCEP ATP III)(Citation14). In the present study a cutoff point of fasting plasma glucose ≥ 100 mg/dL was used to define metabolic syndrome (Citation15). In addition, height and weight were measured to calculate BMI. All blood samples were drawn after an overnight 12-h fast. Fasting plasma glucose (FPG), total cholesterol, triglycerides and high-density lipo-protein (HDL) cholesterol were measured. Low-density lipoprotein (LDL) cholesterol was calculated using Friedewald's formula. LDL was treated as missing in subjects with extremely high value of triglycerides level (TG >500 mg/dl) (n=33).
All subjects went through general health questionnaires. Detailed information was acquired by asking about use of antihypertensive medication, educational level, monthly cost of living, past history of CVD, family history, smoking, alcohol consumption, amount of exercise and dietary habits including balanced diet, salty diet, dairy diet, high protein diet and vegetarian diet. We measured the dietary habits in terms of how frequently the subjects were eating the specific food items per day (Citation16). Using additional salt whenever a subject eats out was defined as a salty diet. Eating meat, fish, eggs or beans more than twice per day was defined as a high protein diet. Eating vegetables at least two times per day was defined as vegetarian diet. Dairy diet was defined as eating milk, yogurt or ice cream at least once per day. Eating over 20 kinds of the food items including meat, fish, vegetable, fruit and rice in a day was defined as a balanced diet (Citation17). A small amount of exercise was defined as less than 7.5 kcal/kg per week, based on that an intermediate amount of exercise (3 metabolic equivalents; 3 MET) was determined as exercising five times per week for 30 min, which is equivalent to 7.5-10.5 kcal/kg per week (Citation18). Alcohol consumption was calculated as weight (g) on the basis of kinds of alcohol, drinking amount, consumption frequency and drinking duration.
Hypertension was defined according to JNC 7 as systolic blood pressure (SBP) ≥140 mmHg or diastolic blood pressure (DBP) ≥90 mmHg. Controlled blood pressure was also defined as SBP <140 mmHg and DBP <90 mmHg, or SBP <130 mmHg and DBP <80 mmHg for subjects with diabetes (Citation4,19).
Data analysis
All statistical analyses were performed using SAS 9.01 for Windows. A χ2 test was performed to test for differences of proportion of multiple variables, and a t-test was performed to evaluate the difference between the mean of two variables. Mantel-Haenszel statistics were used to discern trends in the prevalence of each age group. Multiple logistic regression analyses were performed to assess significant associations between the characteristics of subjects that were related to hypertension and their control of blood pressure. Variables of p-value <0.25 in the univariate test were selected as candidates for the multivariate model along with all variables known as being related to hypertension control. For these multiple logistic regression analyses, two models were used on both sexes. One model included demographic, anthropometric and biochemical variables. In addition, lifestyle factors including smoking, alcohol intake, exercise and dietary habit were added in the other model. The odds ratio and 95% confidence intervals (CI) were calculated. To evaluate the descriptive power of the model, a value of Max-rescaled r2 was used. All two-tailed p-values <0.05 were regarded as indicating statistical significance.
Results
Self-reported diagnosis, treatment and control in men and women.
Although 38.3% reported that they were hypertensive and most of these (93.5%) were receiving treatment for hypertension, only 22.3% of treated hypertensive subjects had controlled blood pressure. The prevalence of controlled hypertension was not significantly different in both sexes ().
Table I. Prevalence of self-reported diagsnosis, treatment and control in men and women.
Distribution of blood pressure control by sex and age.
shows the difference in blood pressure control between men and women by age groups. Women diagnosed with hypertension controlled their blood pressure better than men in all age groups except 80 years and older. Men had a pattern of increasing rate of control with age. However, these results are not significant.
Figure 1. Control rate of hypertension in men and women diagnosed with hypertension (Mantel-Haenszel χ 2 = 2.190, p = 0.139 in men, Mantel-Haenszel χ 2 = 0.179, p = 0.673 in women, respectively).
shows the distribution of uncontrolled systolic blood pressure or diastolic blood pressure in both sexes by age groups. In women diagnosed with hypertension, the prevalence of uncontrolled systolic blood pressure increased significantly with age (P for trend=0.038).
Figure 2. Distribution of uncontrolled hypertension in men (a) and women (b) diagnosed with hypertension by age group (Mantel-Haenszel χ 2 = 3.413, p = 0.065 in men; Mantel-Haenszel χ 2 = 4.302, p = 0.038 in women, respectively).
General characteristics of hypertensive subjects with controlled blood pressure and hypertensive subjects with uncontrolled blood pressure
The demographic characteristics, health-related behaviors and lifestyle factors for hypertensive subjects are shown in . The proportion of uncontrolled blood pressure was higher in men (p=0.040). Subjects who had uncontrolled blood pressure had higher pulse pressure (p<0.001), BMI (p<0.001), waist circumference (p<0.001) and fasting blood glucose (p<0.001). The proportion of metabolic syndrome (p=0.005) and past history of diabetes (p<0.001) were significantly higher in the group with uncontrolled blood pressure. No significant differences among lifestyle-related variables including smoking, alcohol intake and exercise and dietary habits were found between the two groups, except for the lower balanced diet in the group with uncontrolled blood pressure ().
Table II. General characteristics of hypertensive subjects with controlled blood pressure and hypertensive subjects with uncontrolled blood pressure.
Characteristics of hypertensive men and women with controlled blood pressure and hypertensive men and women with uncontrolled blood pressure
BMI was higher in men with uncontrolled blood pressure group than in the controlled blood pressure group (p=0.012). Pulse pressure (p<0.001) and FPG levels (p=0.010) were significantly higher in men with uncontrolled blood pressure than those with controlled blood pressure. Men with uncontrolled blood pressure were more likely to have history of diabetes. Men with controlled blood pressure had an increased prevalence of balanced diet (p=0.003). Women who had higher abdominal obesity (>80 cm) (p=0.003), higher BMI (p=0.004), history of diabetes and higher pulse pressure (p<0.001) were more likely to have uncontrolled blood pressure ().
Table III. Characteristics of hypertensive men and women with controlled blood pressure and hypertensive men and women wit uncontrolled blood pressure.
Factors associated with blood pressure control.
shows the adjusted odds ratios of all variables relative to control of hypertension. In men, higher BMI was significantly associated with uncontrolled hypertension using model 1 (p=0.015). After controlling lifestyle-related variables (model 2), higher BMI was also significantly associated with uncontrolled hypertension (p=0.045). In addition, higher FPG (p=0.049) was significantly associated with uncontrolled hypertension, and a past history of CVD (p=0.038) and balanced diet (p<0.001) were significantly associated with controlled blood pressure. In women, a waist circumference of over 80 cm was significantly associated with uncontrolled hypertension in both models (p=0.007 and p=0.009, respectively).
Table IV. Factors associated with uncontrolled hypertension in subjects diagnosed with hypertension.
Discussion
Most elderly people (≥60 years old) diagnosed with hypertension were on hypertensive medications. Of the subjects diagnosed with hypertension, 93.5% were taking hypertension medications, but only 22.3% of treated persons had control of their blood pressure (). This result differs from those of the other studies which reported lower treatment rates and higher control rates (Citation6,20,21). In terms of lower control rate, most people in this study have a low level of education () that might be related to a lack of knowledge about complications and a lack of strict compliance (Citation22).
From , old-aged women in our study had systolic hypertension of a prevalence similar to other studies (Citation7,23). In women diagnosed with hypertension, the prevalence of uncontrolled systolic blood pressure increased significantly with age. It is consistent with a study which showed a high prevalence of uncontrolled systolic hypertension in women (Citation23), which might be explained by the fact that systolic blood pressure in postmenopausal women might be affected by vascular degenerative process (Citation24).
High BMI (over 23 kg/m2) in men and high waist circumference (over 80 cm) in women diagnosed with hypertension were negatively associated with blood pressure control in this study. In those who are diagnosed with hypertension, control of blood pressure can be obtained by reduction of body weight and this phenomenon has been observed in other studies (Citation25-27). In one Korean study, a BMI under 23 kg/m2 was related to controlling diagnosed hypertension (Citation28) , and a BMI over 25 kg/m2 in old-aged men was associated with uncontrolled high blood pressure in a Norwegian study (Citation29). In old-aged women who were diagnosed with hypertension, high waist circumference (over 35 inches) was reported to be associated with uncontrolled blood pressure (Citation30). The association between abdominal obesity and uncontrolled hypertension in these postmenopausal women who may have decreased level of estrogen might also be explained by the antihypertensive effect of estrogen (Citation31). Based on these results, we believe that hypertensive elderly people may need to reduce their weight for blood pressure control. However, further intervention studies may be warranted to elucidate the association between obesity and blood pressure control by gender in elderly hypertensive subjects.
Low salt diet (Citation32), low fat diet and high fiber diet (Citation33) were reported to be related to controlled hypertension. Balanced diet was found to be associated with controlled hypertension in men in this study. In one study in France, less well-balanced diet was shown to be associated with hypertension (Citation34). In addition, in a randomized clinical trial (Citation35), balanced diet was proven to have an effect on controlling hypertension in both sexes. The association between balanced diet and controlled hypertension in women in this study was not significant after adjusting for other covariates, although an odds ratio with nearly marginal significance has a favorable effect on controlled hypertension in terms of its direction. Further studies will be necessary to clarify the gender difference in the association between uncontrolled hypertension and balanced diet.
We need to focus on the family history of men diagnosed with hypertension, because a family history of CVD was associated with better control of blood pressure in men (Table IV). It can be inferred that men with a family history of CVD pay more attention to their health than if they did not have a family history of CVD and this could be a kind of educational effect for men diagnosed with hypertension. Pulse pressure, reported as a prognostic factor for hypertension (Citation36), is more important than isolated systolic hypertension in severe hypertension (Citation37). The latter study showed that a pulse pressure <60 mmHg is associated with three times lower risk than a pulse pressure >70 mmHg in subjects ≥60 years old. and show that blood pressure control was also closely associated with lower pulse pressure (<60 mmHg), which suggests that people who have controlled blood pressure might have a good prognosis in terms of a lower likelihood of complications such as coronary artery disease (Citation37). However, we cannot determine that high pulse pressure is a cause or a consequence of uncontrolled hypertension in this cross sectional study design.
Our study has limitations that should be considered. In terms of the cross sectional study design, we have difficulty determining the causality in regard to observed relationship between the factors and blood pressure control. In addition, we could not collect enough information about the medication which the subjects diagnosed with hypertension were taking. Further study needs to be performed to investigate the factors related to blood pressure control in old hypertensive subjects based on the drug classes.
In summary, the present study suggests that in elderly people (≥60 years old) diagnosed with hypertension general obesity (high BMI) appears to have an important influence on uncontrolled hypertension in men, whereas abdominal obesity (high waist circumference) appears to be an important factor in women. Further intervention studies may be warranted to elucidate the association between obesity and blood pressure control by gender in elderly hypertensive subjects.
Acknowledgements
We would like to thank Andrew J. Schrage for assistance in revising the manuscript. We would also like to thank the personnel of the Chungju Public Health Center for recruiting the study participants as well as for collecting the data for this study. Furthermore, we would like to thank all the participants in this study. This study was supported by the grants from the “2003–2005 Korea Health Promotion Research Program” of the Ministry of Health and Welfare, Republic of Korea.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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