Introduction
Hypertension is a common disease and major risk factor for coronary ischemia, stroke, renal failure, and mortality (Williams et al., 2018; World Health Organization, 2019). In 2018, hypertension was the eighth most common cause of death in Taiwan (Health Promotion Administration, Ministry of Health and Welfare, Taiwan, ROC, 2020). According to the World Health Organization, 40% of the world's population over the age of 25 years (about one billion people) had hypertension in 2008, with 1.56 billion people expected to experience hypertension worldwide by 2025. Approximately eight million people die each year from hypertension-related diseases (Williams et al., 2018). The prevalence of hypertension is on the rise (Fryar et al., 2017; Health Promotion Administration, Ministry of Health and Welfare, Taiwan, ROC, 2017), and reducing the prevalence of hypertension is a worldwide health goal (World Health Organization, 2016). Therefore, the prevention and treatment of this disease are challenges for healthcare professionals worldwide.
Studies have shown the risk factors of essential hypertension to include genetics, gender, age, body mass index (BMI), socioeconomic status, eating habits, smoking, drinking, stress, emotional state, hyperlipidemia, and hyperuricemia, among others (Lu et al., 2015; H. C. Wang et al., 2012; World Health Organization, 2019; Yang et al., 2012; Zekewos et al., 2019). However, the cause of hypertension remains unknown in most cases (Bolivar, 2013). Further investigation is needed, because pinpointing the risk factors of this disease will aid in its prevention and treatment.
Body constitution, which refers to the fundamental components that constitute a human being, includes the total expression of physiological, psychological, and pathological traits (Su et al., 2008; Q. Wang, 2012). In addition, body constitution may reflect the state of balance between the yin and the yang and their related functions (Su et al., 2008). Su et al. defined body constitution as the physiologic state maintained by the dynamic interaction of energy (yang) and materials (yin) within the body. Body constitution deviation is defined as an imbalance in the consumption of yin and yang (L. L. Chen et al., 2009; Su et al., 2008). Having a "Yang-Xu constitution" implies that the energy needed to maintain bodily functions has diminished, which may be expressed in subjective symptoms such as fatigue, shortness of breath, chills, and loose stools (Su et al., 2008). Having a "Yin-Xu constitution" implies that the materials needed to perform or maintain body function have diminished, which may result in subjective symptoms such as thirst, hot flushes, and hard stools (J. D. Lin, Chen, et al., 2012; J. S. Lin et al., 2012). Having a "stasis constitution" implies that the dynamic interaction between yin and yang has slowed down and is less efficient, which may lead to subjective symptoms such as dizziness, chest tightness, or numbness in the limbs (J. D. Lin, Lin, et al., 2012). Traditional Chinese medicine (TCM) experts have suggested a correlation between body constitution and the occurrence and progression of disease and that individuals with unbalanced body constitutions are susceptible to certain pathogenic factors and related diseases (Su et al., 2008; Sun et al., 2018; Q. Wang, 2012). Implementation of appropriate care measures such as emotional management, exercise, suitable lifestyle, and living environment after detection of body constitution deviation and in accordance with body-constitution deviation type may reduce the occurrence and recurrence of disease (Shen et al., 2010; Q. Wang, 2012; Q. Wang et al., 2018). Therefore, this study was developed to explore the relationship between type of body constitution deviation and essential hypertension. The findings are provided as a reference for preventing essential hypertension.
In recent years, the World Health Organization has advocated a combination of traditional medical measures to prevent and treat diseases (World Health Organization, 2013). TCM is commonly combined with conventional Western medicine to treat hypertension in Chinese around Asia and in Chinese populations elsewhere in the world (Fan et al., 2019; J. Wang & Xiong, 2013). Only a few studies in Mainland China have correlated essential hypertension with phlegm wetness, Yin-Xu, blood stasis, and qi deficiency body constitution (Y. Li et al., 2017; Zhu et al., 2017). However, other studies have shown that living environment may affect body constitution status and subsequently affect the physical response to pathogenic factors of diseases (L. Li et al., 2019). Additional studies are required among Chinese populations in areas outside Mainland China to elucidate the relationship between TCM body constitution and hypertension. No research on the relationship between type of body constitution deviation and essential hypertension has been conducted in Taiwan. Therefore, this study was developed to explore the association between TCM body constitution deviation and essential hypertension among residents in Taiwan. The result of this study provides empirical evidence to help governments and healthcare professionals plan healthcare strategies to prevent essential hypertension.
Methods
Study Design and Participants
Study design and setting
A case-control study design and a purposive sampling strategy were adopted. The participants were selected from the cardiac clinic of a regional hospital and the community health checkup program in a neighboring community in southern Taiwan. Physicians confirmed the presence/absence of essential hypertension during regular patient health checkups.
Estimation of sample size
A pilot study comprising 29 patients with essential hypertension and 29 without hypertension was conducted to select cases meeting the inclusion conditions. The results were used to calculate the number of participants needed and the Cronbach's [alpha] values for the questionnaire. When comparing the average body constitution scores, the difference in stasis was the smallest between the hypertension and nonhypertension groups, which were 26.03 +/- 8.72 and 23.03 +/- 7.46, respectively. G*Power 3.1 statistical software was used to calculate the sample size needed for t test. Setting the [alpha] error probability to .05 and the power (1 - [beta] error probability) to 0.95, 384 participants were required. The number of required participants was increased by 10% to 420 to account for possible participant attrition during the study.
Sample
The inclusion criteria for the hypertension group included the following: (a) diagnosis of essential hypertension by a physician or in the two measurements (taken at an interval of 30 minutes) at the time of recruitment and (b) systolic blood pressure of >= 140 mmHg or diastolic blood pressure of >= 90 mmHg (the Seventh Report of the Joint National Committee criteria for diagnosing hypertension). The inclusion criteria for the nonhypertension group included the following: (a) the absence of hypertension confirmed by a physician and blood pressure readings at the time of recruitment of < 140 mmHg (systolic) and < 90 mmHg (diastolic). The participants in both groups were all between 20 and 80 years old. All of the participants could communicate, were willing to participate, and signed consent forms. The exclusion criteria for both groups were as follows: the presence of other chronic diseases, severe acute illness within the past 3 months, continued use of drugs that affect blood pressure, and pregnancy. From August 2014 to July 2015, 210 participants with hypertension and 210 participants without hypertension were recruited (Table 1). Because age and gender affect TCM body constitution and blood pressure (National Health Bureau, Department of Health, Executive Yuan, Taiwan, ROC, 2011; Sun et al., 2018), the participants were first stratified by presence or absence of hypertension and then by gender and age. The age interval of each stratum was 20 years, as recommended by the National Surveillance Definitions for Hypertension in the United States (Fryar et al., 2017). In accordance with the stratification conditions, the number of participants with and without hypertension in each group was selected as 1:1 using purposive sampling. However, as cases of essential hypertension among younger-aged individuals are less common, only 10 younger participants (< 40 years old) were recruited, with five assigned to each group, respectively.
Measurements
A questionnaire survey method was used in this study. The measurement tools used were structured questionnaires and included the TCM Body Constitution Questionnaire (BCQ; L. L. Chen et al., 2009; J. D. Lin, Chen, et al., 2012; J. D. Lin, Lin, et al., 2012; J. S. Lin et al., 2012; Su et al., 2008), the Five Emotions Questionnaire (M. H. Wang, 1995), and a demographics and hypertension-related factors datasheet. The published versions of the BCQ and the Five Emotions Questionnaire were used with permission from the original authors. In addition, blood pressure was measured twice at recruitment using an electronic sphygmomanometer to determine the case grouping.
Traditional Chinese medicine Body Constitution Questionnaire
The BCQ developed by Su et al.'s research team in Taiwan (L. L. Chen et al., 2009; J. D. Lin, Chen, et al., 2012; J. D. Lin, Lin, et al., 2012; J. S. Lin et al., 2012; Su et al., 2008) was used to measure TCM body constitution deviation. In the study questionnaire used in this study, the concepts of yang and yin were used in their broadest sense, with yang including the function of qi, yin including the function of blood, and stasis including the function of phlegm dampness (J. D. Lin, Lin, et al., 2012; Su et al., 2008). The BCQ comprised three parts, as follows: assessment of Yin-Xu constitution (BCQ-; 19 questions including blood deficiency), assessment of Yang-Xu constitution (BCQ+; 19 questions including qi deficiency), and assessment of stasis constitution (BCQS; 16 questions including phlegm dampness). Some questions were shared by the three scales, and the total number of questions in the BCQ was 44. The questionnaire was completed by the participants, based on their perceived intensity or frequency of physical symptoms during the past month. A 5-point Likert scale was used for scoring, as follows: 1 = not at all/never, 2 = slightly/occasional, 3 = moderate/half of the time, 4 = severe/very often, and 5 = very severe/always. The score for each BCQ was calculated separately, with the scores for BCQ- (BCQ to assess Yin-Xu) ranging from 19 to 95, those for BCQ+ (BCQ to assess Yang-Xu) ranging from 19 to 95, and those for BCQS (BCQ to assess stasis) ranging from 16 to 80. A higher score on the BCQ-, BCQ+, or BCQS was interpreted to indicate, respectively, a more pronounced Yin-Xu, Yang-Xu, or stasis constitution (L. L. Chen et al., 2009; J. D. Lin, Lin, et al., 2012; J. S. Lin et al., 2012), and the total score of each BCQ was used in this study to indicate whether the participant had a Yin-Xu, Yang-Xu, or stasis constitution. Participants with a total BCQ- score >= 29.5 were categorized as having a Yin-Xu constitution, participants with a total BCQ+ score >= 30.5 were categorized as having a Yang-Xu constitution, and participants with a total BCQS score >= 26.5 were categorized as having a stasis constitution (L. L. Chen et al., 2009; J. D. Lin, Lin, et al., 2012; J. S. Lin et al., 2012).
Using the BCQ- to assess Yin-Xu constitution (J. D. Lin, Chen, et al., 2012; J. S. Lin et al., 2012) earned a Cronbach's [alpha] value of .85 and a retest reliability intraclass correlation coefficient (ICC) value of .91. Using the BCQ+ to assess Yang-Xu constitution (L. L. Chen et al., 2009; J. D. Lin, Lin, et al., 2012; Su et al., 2008) earned a Cronbach's [alpha] value of .88 and a retest reliability ICC value of .91. Using the BCQS to assess stasis constitution (J. D. Lin, Lin, et al., 2012) earned a Cronbach's [alpha] value of .88 and a retest reliability ICC value of .92. The Cronbach's [alpha] values of the BCQ-, BCQ+, and BCQS pilot studies were .85, .86, and .86, respectively.
Five Emotions Questionnaire
The Five Emotions Questionnaire developed by M. H. Wang was used in this study to measure anger, joy, worry, sadness, and fear. Participants used the questionnaire, with five questions related to each emotion, to self-assess their emotional state during the past month (M. H. Wang, 1995). Approval was given by the original author to change the scale from a 4-point scale to a 5-point Likert scale. Each question was scored as follows: 1 = not at all, 2 = occasionally, 3 = half of the time, 4 = often, and 5 = always. The total possible score for each emotion category ranged from 5 to 25 points, with higher scores associated with a higher likeliness of occurrence of the associated emotional tendency (M. H. Wang, 1995). This study tested the Cronbach's [alpha] values of anger, joy, worry, sadness, and fear as .68, .72, .57, .87, and .75, respectively.
Demographics and hypertension-related factors questionnaire
This questionnaire gathered data on the basic demographics, blood pressure values, hypertension-related lifestyles, personal habit factors (i.e., staying up late, smoking, drinking, eating unhealthy foods, and regular exercise), and disease factors (i.e., hyperlipidemia or hyperuricemia) of participants. Questions regarding habits and disease factors were binary yes/no answers. Regular exercise referred to performing at least 30 minutes of continuous exercise, and staying up late referred to going to sleep after midnight. Two TCM physicians and three nursing experts were asked to check the applicability and relevance of the question contents. The expertise of nursing experts included TCM nursing and adult nursing. The content validity index value was 1, indicating that all of the questions were applicable, although the wording of some questions required modification.
Electronic sphygmomanometer
Blood pressure was measured using an electronic sphygmomanometer (UDEX-Twin; Elquest Corporation, Inc., Chiba, Japan) to confirm the hypertension status of each participant. The sphygmomanometer was certified under international standards and was maintained and calibrated to regularly ensure numerical accuracy. The measurement range of the sphygmomanometer was 10-285 mmHg, and the error value was +/- 3 mmHg.
Data Collection and Analysis
This study was approved by the institutional review board (No. B10303010). All of the questionnaires were collected by the same researcher, who had received prior training. Blood pressure readings were taken by another researcher to increase the consistency of the data collection process. Both were registered nurses with clinical experience. The data collection sites were the outpatient waiting area and the community activity center of a regional teaching hospital in southern Taiwan. Eligible patients were invited to participate in the study and, if willing, were asked to provide written informed consent. After an explanation of the study process and participant rights, the participants completed the questionnaires. If participants were unable to fill out the questionnaires independently, the researcher recorded their answers for them. All of the participants had their blood pressure measured once, respectively, before and after completing the questionnaire to determine the presence or absence of hypertension.
Statistical analysis was performed using SPSS Statistics 22.0 software (IBM, Inc., Armonk, NY, USA). A chi-square test, an independent t test, and a multivariate logistic regression were used to analyze the influence of the presence or absence of hypertension by TCM body constitution, the five emotions, and demographic/hypertension-related factors. The p value was arbitrarily set at .05 to test the hypothesis based on Type I error ([alpha] = .05), as the results of univariate analysis may be biased by other variables and the pseudo-association between independent variables may confound the "true" difference between two groups. Because the p value and search for significance level may be used as decision criteria (Dahiru, 2008; Greenland et al., 2016), the borderline level of significance was reset in this study to .10 ([alpha] = .1), making the test of significance in the univariate analysis less stringent to include the variables of weak evidence against null effect in multivariate logistic regression analysis for adjusting the important confounders.
Results
The study recruitment period was between August 2014 and July 2015. Four hundred forty questionnaires were completed by participants who met the criteria for inclusion. Questionnaires from individuals with no history of hypertension and for whom hypertension was detected in only one of the measurements were excluded. Four hundred twenty (95%) of the completed questionnaires (210 in the hypertension group and 210 in the nonhypertension group) were valid and included in the analysis. The hypertension group included 138 participants (65.7%) from the community and 72 (34.3%) from the cardiology outpatient department of the target hospital. The nonhypertension group included 180 participants (85.7%) from the community and 30 (14.3%) who were family members accompanying outpatients at the hospital.
Distribution and Analysis of Demographics, Lifestyle, Five Emotions, and Traditional Chinese Medicine Body Constitution Status in Patients With/Without Hypertension
The data regarding the demographics, lifestyle, five emotions, and TCM body constitution status of the participants are shown in Tables 1 and 2. For participants in the hypertension and nonhypertension groups, respectively, the mean ages were 59.68 +/- 11.27 years (range: 27-80 years) and 58.14 +/- 10.32 years (range: 26-80 years), the systolic blood pressure readings at the second measurement were 141.64 +/- 17.43 and 118.43 +/- 10.39 mmHg, the diastolic blood pressure readings were 84.67 +/- 10.97 and 73.68 +/- 7.81 mmHg, the percentages having Yin-Xu constitutions were 44.8% and 28.6%, the percentages having Yang-Xu constitutions were 32.4% and 25.2%, and the percentages having stasis constitutions were 30.6% and 19.6%. The hypertension group had higher mean emotional and life-stress scores than the nonhypertension group. Moreover, the proportions of participants with hyperlipidemia, hyperuricemia, and Yin-Xu, Yang-Xu, and stasis constitutions in the hypertension group were higher than those in the nonhypertension group. Chi-square tests and independent t tests were performed on factors affecting the presence or absence of essential hypertension, with results showing statistically significant differences between the two groups (p < .05) in terms of BMI; drinking habit; hyperlipidemia or hyperuricemia; the emotional traits of anger, worry, and fear; and having a Yin-Xu or stasis body constitution (Tables 1 and 2). However, the lifestyle was similar between the two groups (p > .05).
Correlation Between Traditional Chinese Medicine Body Constitution Deviation and Essential Hypertension
The variables with a p value < .1 in the univariate analysis results were included in the multivariate logistic regression analysis to adjust for interfering factors. The factors affecting the presence or absence of essential hypertension are summarized in Table 3, with results showing statistically significant differences between the two groups in terms of age, BMI, hyperlipidemia, and Yin-Xu constitution (p < .05). After adjusting for the other variables, the odds of hypertension were shown to increase by an average of 1.03 times for every 1-year increase in age and 1.25 times for every 1 kg/m2 of BMI increase. Furthermore, the odds of hypertension in those with a history of hyperlipidemia were found to be 2.63 times higher than in those without this history, and the odds of hypertension in those with Yin-Xu constitution were found to be 2.15 times than in those without Yin-Xu. This indicates that, after adjusting for demographics and other related factors, the risk of developing hypertension is higher in those with Yin-Xu constitution than in those without Yin-Xu.
Discussion
This study found BMI; having hyperlipidemia or hyperuricemia; having the emotional traits of anger, worry, or fear; and having a Yin-Xu or stasis constitution to be correlated with essential hypertension. After adjusting for other potential variables, having a Yin-Xu constitution was identified as a risk factor for essential hypertension. This finding provides empirical evidence for governments and healthcare professionals to enact measures to prevent essential hypertension. The results suggest that the TCM BCQ may be used to screen people with Yin-Xu and stasis constitutions, with the results used to provide appropriate conditioning body-constitution care measures to reduce exposure to the risk factors of essential hypertension.
The scales of three TCM body constitution types developed by Su et al. were used in this study (L. L. Chen, et al., 2009; J. D. Lin, Chen, et al., 2012; Lin, Lin, et al., 2012; J. S. Lin et al., 2012; Su et al., 2008), with the results showing the proportions of people with Yin-Xu, Yang-Xu, and stasis constitutions were higher in the hypertension group than in the nonhypertension group. This finding is similar to the results of previous studies (Cen & Liu, 2016; Wu et al., 2009; Zhu et al., 2017) that used the scales of nine TCM body constitution types developed by Q. Wang et al. (2006). Furthermore, the results of this study indicate that those with TCM body constitution deviations are more prone to essential hypertension than those without body constitution deviations, which is consistent with the theory that disease occurrence is correlated with body constitution deviation (Sun et al., 2018).
Further analysis in this study showed both having a Yin-Xu constitution and having a stasis constitution to be correlated with essential hypertension. In addition, the stasis constitution measurement in this study included phlegm dampness (J. D. Lin, Lin, et al., 2012). Therefore, the result of this study is similar to that of Zu et al. (2013), which showed that Yin-Xu, phlegm dampness, and blood stasis influence the prevalence of hypertension. Moreover, this study also compared the body constitution differences between prehypertension and healthy individuals, finding that Yin-Xu, phlegm-dampness, and blood stasis constitution influence prehypertension. Yin-Xu produces internal heat that disturbs the orifices, causing hyperactivity of the yang, which is one of the main risk factors for hypertension (H. J. Chen & Dung, 2014). Phlegm dampness blocks the meridians and turns into heat, which disturbs the orifices and causes hypertension. In addition, retention of phlegm and fluid causes poor blood circulation, resulting in stasis, which may aggravate hypertension (H. J. Chen & Dung, 2014; J. Wang & Xiong, 2012).
As some of the risk factors of essential hypertension could not be controlled in this study, a multivariate logistic regression model was employed to adjust for the potentially interfering factors. The results of this model showed only Yin-Xu constitution as associated with essential hypertension, which differs partially from the findings of previous studies (Cen & Liu, 2016; Y. Li et al., 2017; Wu et al., 2009; Zhu et al., 2017). This difference may be because a different body constitution questionnaire and classifications were used, the living environments of participants were significantly different, and related interfering factors may not have been included in the multivariate logistic regression model analysis. The body-constitution classifications and measurement questions used in previous studies differed from those used in this study (Cen & Liu, 2016; Y. Li et al., 2017; Wu et al., 2009; Zhu et al., 2017). In addition, previous studies may have included different interfering factors in the multivariate regression model analysis to adjust for the effects of other variables (Cen & Liu, 2016; Y. Li et al., 2017; Wu et al., 2009).
The stratified sampling approach used in this study excluded some potential research subjects and utilized multivariate regression model analysis to adjust for confounding factors and to reduce error (Portney & Watkins, 2009). It has been reported that, as body constitution distribution differs by gender and age group, gender and age are correlated with the occurrence of essential hypertension (National Health Bureau, Department of Health, Executive Yuan, Taiwan, ROC, 2011; Williams et al., 2018). Therefore, this study used stratified sampling so that the two groups were similar in terms of gender and age to adjust for the potential interference of these two variables on the relationship between TCM constitution deviation and essential hypertension. Moreover, the sources of subjects for the two groups were similar, which may have reduced case-selection-related errors (Portney & Watkins, 2009). Blood pressure was measured twice at recruitment to improve the accuracy of participant groupings. To avoid the influence of chronic diseases other than hyperlipidemia and hyperuricemia on TCM body constitution distribution (S. C. A. Lin et al., 2017; Zhu et al., 2017), individuals with other chronic diseases were excluded.
However, the participants in this study had already developed the disease, which may have influenced the results. In other words, although this study found Yin-Xu constitution as correlated with essential hypertension, it is impossible to judge the order of occurrence of Yin-Xu constitution and essential hypertension. Longitudinal design studies that incorporate the BCQ into the follow-up study plan of the National Health Interview Survey (Health Promotion Administration, Ministry of Health and Welfare, Taiwan, ROC, 2017) are needed to further explore the causality between Yin-Xu and essential hypertension.
Limitations
Nearly half of the participants in this study were over 60 years old. Elderly individuals may be more likely to miss questions and may be less clear about their own disease status than younger individuals (Tsai et al., 2007). Thus, recall bias may have been an unavoidable limitation in this study. Some of the participants in the hypertension and nonhypertension groups (3.3% and 2.9%, respectively) required assistance with recording their answers because of their visual deterioration or illiteracy. This process may not completely avoid errors in data collection. However, the average ages of the participants in the two groups were similar. Thus, these errors may be expected to be consistent between the two groups. To further reduce error, the study process and recruitment criteria were explained in detail. Blood pressure was measured before and after the questionnaire was completed to improve the accuracy of subject grouping. The interviewer's manual was prepared before implementation of the study to maintain consistency and to reduce data collection errors. Because the participants had no other chronic diseases and as there were significantly fewer patients with hypertension below the age of 40 years, the results of this study should not be inferred to patients with hypertension with other comorbidities or to patients with hypertension less than 40 years old.
Conclusions
The results of this study established the empirical data necessary to confirm a correlation between TCM body constitution deviation and essential hypertension. The results suggest that TCM Yin-Xu and stasis constitutions are associated with essential hypertension. After adjusting for BMI, drinking habit, hyperlipidemia status, hyperuricemia status, emotional traits, and other potential confounding factors, Yin-Xu constitution was found to be a risk factor for the development of essential hypertension. These empirical data may be used as a basis to combine TCM methods in the prevention of essential hypertension. They also provide a reference for governments and healthcare professionals to screen and plan TCM Yin-Xu constitution healthcare strategies to reduce public/patient exposure to the risk factors of essential hypertension.
Acknowledgments
The authors would like to thank the study participants for their participation and the China Medical University (CMU103-S-32) and Buddhist Dalin Tzuchi General Hospital (DTCRD104-E-05), Taiwan, for their funding support.
Author Contributions
Study conception and design: YCL, LLC, JSL
Data collection: YCL, TKL, SCAL, HCW
Data analysis and interpretation: LLC, YCL, HCW
Drafting of the article: LLC, YCL, HCW
Critical revision of the article: LLC, HCW
References