Distress tolerance moderates the relationship between anger experience and elevated blood pressure

Abstract

Previous studies have linked anger to elevated blood pressure. However, the nature of the association between anger and elevated blood pressure is unclear. This study is aimed at investigating the moderating effect of distress tolerance on the relationship between anger experience and elevated blood pressure. A total of 310 patients drawn from a university teaching hospital in southeast Nigeria participated in this study. They comprised 156 men and 154 women who were aged between 20 and 80 years (mean age = 50.45). Participants responded to the measures of distress tolerance and Novaco Anger Inventory—Short Form. The blood pressures of the participants were obtained with sphygmomanometer and stethoscope. The results of the hierarchical multiple regression analysis indicated that anger experience significantly predicted both systolic and diastolic blood pressure. The results also showed that distress tolerance was a significant predictor of systolic and diastolic blood pressure. Distress tolerance moderated the relationship between anger experience and systolic and diastolic blood pressure. The relationships between anger and systolic and diastolic pressure were stronger for patients with low distress tolerance compared to patients with high distress tolerance. It is recommended that psychological interventions aimed at increasing people’s level of distress tolerance are emphasized in the management of elevated blood pressure.

Keywords

Anger experience distress tolerance elevated blood pressure hypertension

Hypertension has been identified as a major cause of coronary heart disease (Mozaffarian et al., 2015), overall mortality worldwide, and indeed a global public health challenge (Forouzanfar et al., 2017; Zhao et al., 2012). The World Health Organization (WHO; 2002) estimated that about 40% of adult of 25 years and above are diagnosed with hypertension and about 1 billion in 2008 are living with the condition with the highest prevalence at 46% in Africa (WHO, 2011). The prevalence of hypertension is also high in Nigeria (Akinlua, Meakin, Umar, & Freemantle, 2015; Ezekwesili, Ononamadu, Onyeukwu, & Mefoh, 2016).

Hypertension is a medical term for high blood pressure (BP) and is described as a chronic medical condition in which the BP in the arteries is persistently elevated (Chobanian et al., 2003). The normal BP is within the range of 100–140 mmHg systolic (top reading) and 60–90 mmHg diastolic (bottom reading). Hypertension is adjudged to be present if the systolic pressure is persistently at or above 140 mmHg and the diastolic pressure is at or above 90 mmHg (Sahraian et al., 2015). Chronic elevation of BP from normal to severe leads to many health complications like coronary heart diseases, accelerated atherosclerosis, renal disease, and stroke (Khakurel, Agrawal, & Hada, 2009).

Several psychological factors have been associated with elevated BP including stress and distress (Gasperin, Netuveli, Dias-da-Costa, & Pattussi, 2009), type A behavior pattern (Lyness, 1993), hostility, depression, stress, and anxiety (Kretchy, Owusu-Daaku, & Danquah, 2014). More specifically, researchers have identified anger as a major factor in elevated BP (Hosseini, Mokhberi, Mohammadpour, Mehrabianfard, & Lashak, 2011; Jorgensen, Johnson, Kolodziej, & Schreer, 1996; Schum, Jorgensen, Verhaeghen, Sauro, & Thibodeau, 2003; Suls, Wan, & Costa, 1995). However, most of the studies on anger and hypertension were conducted in the Western countries with no studies in developing countries of Africa, yet there is a high prevalence of hypertension in the region. What is more, the role of distress tolerance in anger–hypertension relationships has not been previously explored even when distress tolerance has been associated with the ability of individuals to withstand negative emotional states (Leyro, Zvolensky, & Bernstein, 2010).

Anger and essential hypertension

Anger refers to “an unpleasant emotion ranging in intensity from irritation to rage, usually in response to perceived mistreatment or provocation” (Smith, 1992, p. 139). Anger is often associated with excitement which can be seen as the basis for several forms of mental and physical disorders (Sahraian et al., 2015). In addition, Spielberger (1988) distinguished between state and trait anger. State anger focuses on the intensity of the experience of anger as an emotional state, while trait anger focuses on the personality or individual differences in anger-proneness. While state anger may be transitory and reactive to a given situation, trait anger is a disposition that develops into frequent and intense emotion expression. Anger is therefore an internal state that regulates an individual’s interaction with his or environment (del Barrio, Aluja, & Spielberger, 2004). In this study, therefore, anger is conceptualized as trait anger or anger experience.

The major theoretical explanation for the anger–elevated BP relationship centers on the idea that increased cardiovascular reactivity has a causal relationship with the development of elevated BP (Schum et al., 2003). It is assumed that anger triggers off such activation in the sympathetic nervous system leading to an increase in heart rate and BP (Julius & Johnson, 1985). This idea has been supported by research findings (e.g., Everson, Goldberg, Kaplan, Julkunen, & Salonen, 1998). Recent studies (e.g., Hosseini et al., 2011; Sahraian et al., 2015) that compared trait anger among hypertensive and normotensive individuals found that hypertensive individuals scored higher in anger trait than normotensive individuals. Similarly, a study conducted by Ewart, Elder, Smyth, Sliwinski, and Jorgensen (2011) showed that risk of cardiovascular diseases and hypertension was higher in anger-prone individuals. In spite of these findings, no study has examined the role of anger experience in elevated BP among Nigerian population. Studies on hypertension in Nigeria have primarily focused on its prevalence (Akinlua et al., 2015; Ezekwesili et al., 2016). Hence, the first aim of this study is to explore the relationship between the experience of anger and elevated BP among Nigerian patients.

Distress tolerance as a moderator

Although a considerable amount of research evidence showed that anger experience is associated to elevated BP (e.g., Hosseini et al., 2011; Sahraian et al., 2015), the nature of this relationship remains unclear (Hogan & Linden, 2004). Individuals who are prone to anger arousal and provocation may in their lifetime not develop high BP, which probably may have led to the conflicting research findings on anger–BP relationships. While some researchers (e.g., Everson et al., 1998; Harburg, Gleiberman, Russell, & Cooper, 1991) found positive relationship between anger and elevated BP, other research findings (e.g., Schneider, Egan, Johnson, Drobny, & Julius, 1986) did not support such hypothesis. This could be because of the ability of some individuals to withstand and cope with some psychological distress or anger provocation—a concept known as distress tolerance (Simons & Gaher, 2005). Distress tolerance is defined as a person’s capacity to experience and withstand negative emotional and psychological states (Simons & Gaher, 2005). Theoretically, distress tolerance is associated with processes involved in self-regulation which enables the individual to adjust his or her appraisal of challenging situations in order to positively respond to such distress-eliciting contexts (Leyro et al., 2010; Zvolensky, Vujanovic, Bernstein, & Leyro, 2010). Tolerance of temporary psychological discomfort and dealing with difficult emotions could be adaptive, especially when the experience of such negative emotions can lead to healthy behavioral change (Hayes, Wilson, Gifford, Follette, & Strosahl, 1996).

Although it appears that no previous studies have associated distress tolerance to elevated BP, some other negatively related concepts such as psychological distress had been linked to elevated BP (Footman, Roberts, Tumanov, & McKee, 2013). If psychological distress could contribute to elevated BP, the ability to tolerate stress (distress tolerance) would be an important factor in experience of elevated BP. Distress tolerance has also been reported to moderate the negative impact of some psychological phenomenon. For instance, O’Cleirigh, Ironson, and Smits (2007) found that distress tolerance moderated the relationships between major life events and some negative outcomes. Specifically, using hierarchical moderated regression analysis, O’Cleirigh et al. (2007) found that major life events interacted with distress tolerance such that lower distress tolerance and higher life events had a significant relationship with higher levels of depressive symptoms, substance use coping, and alcohol and cocaine use. Distress tolerance has also been noted as a putative or maintenance factor among individuals that are at risk for a variety of psychological disorders (Zvolensky & Otto, 2007). This implies that people with lower distress tolerance may be more prone to respond in a maladaptive way to distressing conditions than persons with higher levels of distress tolerance (Leyro et al., 2010). Thus, the second aim of this study is to establish whether distress tolerance will moderate the relationship between anger experience and elevated BP. We propose that the relationship between anger experience and elevated BP will be stronger for individuals that have low distress tolerance than those with high distress tolerance. We therefore hypothesized that (1) anger experience will significantly predict elevated BP among Nigerian patients and (2) distress tolerance will moderate the relationship between anger experience and elevated BP.

Methods

Participants

The participants of this study were 310 patients drawn from a university teaching hospital in southeast Nigeria. The participants were 50.3% men and 49.7% women. Their ages ranged from 20 to 80 years with a mean age of 50.45 and a standard deviation (SD) of 15.29. The full descriptions of the demographic characteristics of the participants are shown in Table 1.

Table 1.

Demographics and characteristics of the study population.

Variables	Frequency	Percentage
Sample size	310
Gender
Male	156	50.30
Female	154	49.7
Age	20–80 years
Education
No formal education	42	15.5
Primary education	82	26.5
Secondary education	76	24.5
University education	110	35.5
Marital status
Married	234	75
Divorced/widowed	27	8.7
Single	49	15.8
Occupation
Traders	77	24.8
Civil workers	87	28.1
Skilled workers	66	21.9
Farmers	40	12.9
Unspecified	40	12.9
Family history
Yes	192	61
No	118	38.1
Smoking
Yes	55	17.7
No	255	82.3
Exercise
Yes	202	65.2
No	108	34.8
Diabetic
Yes	65	21
No	245	79
Hypertensive patients	189	58.9
Normotensive patients	121	37.7
On hypertensive drug
Yes	181	58.4
No	129	41.6
Body mass index
Underweight	1	.3
Normal weight	44	14.2
Overweight	129	41
Obese	136	43.9

BMI: body mass index.

BMI classification: underweight (BMI = 17–18.49), normal weight (BMI = 18.5–25), overweight (BMI = 25.5–27.49), and obese (BMI = 30 and above).

Instruments

The questionnaire for this study consisted of two parts. Part 1 contains information on the demographic variables (gender, age, education, marital status, and occupation) and risk factors (family history of hypertension, body mass index [BMI], smoking, exercise, and diabetics). Part 2 consisted of the two measures for distress tolerance and anger experience.

The Distress Tolerance Scale (DTS) (Simons & Gaher, 2005) is a 15-item scale with a single second-order general distress tolerance factor and four first-order factors, namely, tolerance, absorption, appraisal, and regulation. In the initial validation of the scale with 645 undergraduates in Study 1 and 823 students in Study 2, Simons and Gaher (2005) showed that the scale is an internally consistent, single-factor measure. In Study 2, the results of the initial factor analysis indicated that the DTS comprised four first-order factors, which are indicators of a single second-order general distress tolerance factor. In other words, a single higher-order distress tolerance factor emerged from the four related factors. The scale had been used in a number of studies (Koball et al., 2015) as a unidimensional scale. The scores range from 15 to 75 with higher scores indicating higher distress tolerance. The response option ranges from strongly disagree (5) to strongly agree (1). In the scale, only Item 6 is scored in a reversed direction. Simons and Gaher (2005) reported the reliability coefficient to be α = .95. For this study, a reliability coefficient (Cronbach’s alpha) of .81 was obtained.

The Novaco (1975) Anger Inventory—Short Form (NAI-S) was used in this study. The NAI-S is a 25-item scale adapted by Devilly (2005) from the long form of NAI which originally has 90 items. The NAI-S is a measure of the degree of provocation or anger people would feel if placed in certain situations. The scale has a five-point response format ranging from very little (1) to very much (5). Devilly (2005) found the NAI-S to be a one-factor measure for anger. Higher scores indicate high anger arousal and experience. Devilly (2005) reported a Cronbach’s alpha of .96. A reliability coefficient (Cronbach’s alpha) of .88 was obtained for this study.

Mercury Sphygmomanometer and Stethoscope (Accoson made in England) were used to measure systolic and diastolic BPs of the participants.

Procedure

The participants were recruited from the following outpatient units of the hospital: cardiology unit (n = 230), surgical unit (n = 50), and general outpatient department (n = 30). Participants’ consents were sought and obtained individually before the beginning of the study. In each of the units, the current systolic and diastolic measures of the participants who consented to take part in the study were measured by the doctors on duty, using sphygmomanometer and stethoscope. Three different BP measurements at an interval of 5 min were obtained for each participant and the averages of the three measurements were used for this study. In order to obtain the BMI of each of the participants, their weight (kg) and height (cm) were assessed. Information on other traditional risk factors (family history of hypertension and diabetics) was obtained from the patient’s hospital records. Four research assistants, two doctors, and one of the authors collected data for the study. A total of 340 copies of the questionnaire were distributed, of which 310 copies were completed and returned (91% return rate).

Ethical considerations

The study was approved by the Ethical Committee of the University of Nigeria Teaching Hospital (Ethical Clearance Certificate No. NHREC/05/01/2008B-FWA00002458-IRB00002323). Informed consent was obtained from all individual participants in the study.

Data analysis

The design of the study was cross-sectional research. The statistics was performed using SPSS version 20. Pearson correlation was first performed to test the correlation among the study variables (see Table 2). To test the predictive values of the independent variables (anger experience, distress tolerance) on the dependent variable (elevated BP), a hierarchical moderated regression analysis was conducted. The procedure for testing moderation as established by Baron and Kenny (1986) indicates that a significant interaction term in the regression analysis is an evidence of the moderated effect of distress tolerance on the relationship between anger experience and elevated BP. In other words, the association between anger experience and elevated BP depends on an individual’s distress tolerance level. Similarly, Anderson (1986) contends that the hierarchical moderated regression analysis is an appropriate method in establishing moderator variables. Adding the variables hierarchically enables us to determine the incremental contributions of the predictors and the moderator variables to elevated BP. This method has also been adopted in many previous studies (e.g., Davids, Roman, & Kerchhoff, 2017; Meckelmann, Pfeifer, & Rauh, 2013). In Step 1 of the hierarchical multiple regression, we controlled for the effects of demographic variables (gender, age, education, marital status) and traditional risk factors (BMI, family history of high BP, smoking cigarettes, exercise, and being on hypertensive drugs). In Steps 2, 3, and 4, anger experience, distress tolerance, as well as the interaction term (which served as the moderator variable) were regressed on both systolic blood pressure (SBP; see Table 3) and diastolic blood pressure (DBP; see Table 4), respectively.

Table 2.

Descriptive statistics and correlation among the study variables.

Variable	Mean	SD	SBP	DBP	Gender	Age	Edu	BMI	FH	SM	EX	HD	DTS	AX	DT
Controlled variables
SBP	144.58	35.01	–
DBP	88.92	15.13	.78**	–
Gen			−.18**	−.13*	–
Age	50.45	15.29	.47**	.35**	−.20**	–
Edu			−.29**	−.26**	.01	−.30**	–
BMI	28.84	4.77	.33**	.32**	−.06	.24**	.06	–
FH			.15**	.11*	−.03	−.05	.02	.07	–
SM			.21**	.13*	−.24**	.01	−.04	.07	.12*	–
EX			−.18**	−.13*	.06	−.19**	.23**	.02	−.13*	−.09	–
HD			.33**	.32**	−.06	.20**	−.12*	.32**	.09	.12*	.04	–
DTS			.28**	.23**	−.10	.23**	.11*	.09	.06	.03	−.12*	.11*	–
AX	84.64	18.29	.37**	.27**	.12*	.11*	−.06	.09	.13*	.13*	−.24**	.01	.15*	–
DT	42.36	11.16	−.59**	−.54**	.05	−.27**	.25**	−.19**	−.13*	−.14*	.19**	−.18**	−.21**	−.29**	–

SD: standard deviation; SBP: systolic blood pressure, DBP: diastolic blood pressure, BMI: body mass index; AX: anger experience, DT: distress tolerance.

Coding is as follows: gender: 0 = Male, 1 = Female; family history of hypertension (FH): 0 = No, 1 = Yes; smoking (SM): 0 = No, 1 = Yes; exercise (EX): 0 = No, 1 = Yes; hypertension drug (HD): 0 = Not on hypertensive drugs, 1 = Yes; Education (Edu): 1 = No formal education, 2 = Primary education, 3 = Secondary education, 4 = Tertiary education; diabetes (DTS): 0 = No diabetes, 1 = Yes.

p < .01; *p < .05.

Table 3.

Hierarchical multiple linear regression and test of the moderator effect of distress tolerance on the relationship between anger experience and systolic blood pressure (SBP).

Variables	Step 1	Step 2	Step 3	Step 4
Variables	β	β	β	β
Controls
Gender	−.03	−.02	−.04	−.04
Age	.29***	.28***	.23***	.22***
No formal education	.08	.10*	.05	.06
Primary education	.18**	.16**	.09	.08
Secondary education	.07	.04	−.02	−.02
Married	.07	.08	.07	.07
Divorced/widowed	.01	.00	−.03	−.02
Body mass index	.11*	.10*	.07	.09*
Family history of hypertension	.09	.07	.04	.01
Smoking cigarettes	.12*	.10*	.08	.07
Exercise	−.05	.00	.02	.05
Patients on hypertensive drugs	.18***	.18***	.14**	.16***
Diabetes	.14**	.12*	.08*	.06
Main effects
Anger experience		.27***	.19***	.21***
Distress tolerance			−.38***	−.37***
Interaction terms
Anger experience ×distress tolerance				−.15***
Adjusted R²	.36***	.43***	.54***	.59***
∆R²	.39***	.07***	.11***	.02***
∆F	14.68***	35.28***	77.59***	14.15***

Coding is as follows: gender: 0 = Male, 1 = female; family history of hypertension: 0 = No, 1 = Yes; smoking: 0 = No, 1 = Yes; exercise: 0 = No, 1 = Yes; patients on hypertensive drugs: 0 = Not on hypertensive drugs, 1 = Yes; education and marital status were dummy coded.

For education, which had four categories, university education was left as a reference variable and, for marital status, being single was kept as a reference variable.

***

p < .001; **p < .01; *p < .05.

Table 4.

Hierarchical multiple linear regression and test of the moderator effect of distress tolerance on the relationship between anger experience and systolic blood pressure (DBP).

Variables	Step 1	Step 2	Step 3	Step 4
Variables	β	β	β	β
Controls
Gender	−.01	.00	−.02	−.02
Age	.15*	.14*	.09	.08
No formal education	.07	.08	.04	.04
Primary education	.08**	.07	−.01	−.02
Secondary education	.05	.03	−.03	−.03
Married	.18*	.19**	.18**	.18**
Divorced/widowed	.07	.06	.03	.04
Body mass index	.10	.09	.07	.08
Family history of hypertension	.04	.02	−.01	−.03
Smoking cigarettes	.12*	.11*	.08	.07
Exercise	−.03	.00	.02	.04
Patients on hypertensive drugs	.20***	.20***	.16**	.17**
Diabetes	.12*	.10*	.06	.05
Main effects
Anger experience		.21***	.12*	.13***
Distress tolerance			−.40***	−.39***
Interaction terms
Anger experience × distress tolerance				−.09*
Adjusted R²	.24***	.28***	.40***	.41***
∆R²	.27***	.04***	.12***	.01***
∆F	8.69*	15.73*	63.36*	3.94*

Coding is as follows: gender: 0 = Male, 1 = Female; family history of hypertension: 0 = No, 1 = Yes; smoking: 0 = No, 1 = Yes; exercise: 0 = No, 1 = Yes; patients on hypertensive drugs: 0 = Not on hypertensive drugs, 1 = Yes; education and marital status were dummy coded.

For education, which had four categories, university education was left as a reference variable and, for marital status, being single was kept as a reference variable.

***

p < .001; **p < .01; *p < .05.

Results

The result in Table 2 showed that all the control variables and traditional risk factors (gender, age, education, BMI, family history of high BP, smoking cigarettes, exercise, and being on hypertensive drugs) were significantly related to both SBP and DBP. The results showed that being male was related to both SBP (r = –.18, p < .01) and DBP (r = –.13, p < .05) and that older age was associated with both SBP (r = .47, p < .01) and DBP (r = .35, p < .01). Education status was negatively related to both SBP (r = –.29, p < .01) and DBP (r = –.26, p < .01), showing the higher the education, the lower the SBP and DBP. The results also showed that BMI was positively related to SBP (r = .33, p < .01) and DBP (r = .32, p < .01) indicating that the higher the BMI, the higher the SBP and DBP. The results also indicate that people who exhibited having family history of hypertension had significantly higher SBP (r = .15, p < .01) and DBP (r = .11, p < .05) compared to individuals without the family history of hypertension. The results revealed that persons who engage in cigarette smoking had significantly higher SBP (r = .21, p < .01) and DBP (r = .13, p < .05) compared to individuals who do not smoke. Also, patients who do not engage in any physical exercise had significantly higher SBP (r = –.18, p < .01) and DBP (r = –.13, p < .05) in comparison to patients who reported engaging in physical exercises. In addition, patients who use hypertensive medication showed significantly higher SBP (r = .33, p < .01) and DBP (r = .32, p < .01) compared to patients who do not use hypertensive medication SBP and DBP. Finally, patients who have diabetes showed significantly higher SBP (r = .28, p < .01) and DBP (r = .23, p < .01) in comparison to patients who are not diabetic.

For the main predictors, Table 2 shows that anger experience and distress tolerance were significantly related to both SBP and DBP. The results showed that anger experience has a significant positive relationship with SBP (r = .37, p < .01) and DBP (r = .27, p < .01) indicating that the higher the anger experience, the higher the SBP and DBP. The results also show that distress tolerance had a significant negative association with SBP (r = –.59, p < .01) and DBP (r = –.54, p < .01) showing that as distress tolerance increases, SBP and DBP decreases.

The hierarchical regression results in Table 3 showed that the demographic variables and traditional risk factors entered in Step 1 of the equation collectively accounted for a significant variance in SBP (∆R² = .39, p < .001). Specifically, the results showed that age was a significant predictor of SBP (β = .29, p < .001) suggesting that the higher the age, the higher the SBP. Primary education (β = .18, p < .01) was a significant predictor of SBP indicating that patients with primary education had significantly higher SBP compared to those with higher levels of education. BMI was a significant positive predictor of SBP (β = .11, p < .05) showing that the higher the BMI, the higher the SBP. Family history of hypertension (β = .09, p < .05) significantly predicted SBP. This reveals that patients with the family history of hypertension showed higher SBP than those without. Smoking cigarettes (β = 12, p < .05) was a significant predictor of SBP indicating that patients who smoke cigarettes exhibited higher SBP than those who do not. The results also showed that patients who were on hypertensive drugs showed higher SBP (β = .18, p < .01) compared to those who were not on hypertensive drugs. Diabetes significantly predicted SBP (β = .14, p < .01). This indicates that individuals who are diabetic exhibited higher SBP compared to patients without diabetes.

When the main predictor—anger experience—was entered in Step 2 of the regression analysis, it contributed a significant variance in SBP (∆R² = .07, p < .001). The results show that anger experience is a significant positive predictor of SBP (β = .27, p < .001), even when the variance due to the demographic variables and traditional risk factors was controlled. This implies that the higher the anger experience, the higher the SBP, suggesting that patients who have higher trait anger were more likely to have increased SBP than patients low in trait anger. As expected, distress tolerance significantly predicted SBP (β = –.38, p < .001), contributing to an additional 11% variance (∆R² = .11, p < .001) in SBP over the contributions of the demographic variables, traditional risk factors, and anger experience. This implies that the higher the distress tolerance, the lower the SBP. Inclusion of the interaction term (anger experience and distress tolerance) in the fourth regression model contributed a significant variance (∆R² = .02, p < .001) in SBP and was a significant predictor (β = –.15, p < .001) of SBP. This showed that distress tolerance moderated the relationship between anger experience and SBP. In other words, the effect of anger experience on SBP depends on an individual’s distress tolerance level.

The simple slope (Figure 1) showed that anger experience had a significant relationship with SBP for patients with low distress tolerance compared to those with high distress tolerance. The graphs indicate that individuals with higher distress tolerance had lower scores in SBP than those with low distress tolerance, irrespective of their levels of anger experience.

Figure 1.

Graph showing the moderating role of distress tolerance on the relationship between anger experience and SBP.

The results (Table 4) showed that the demographics and traditional risk factors entered in Step 1 of the regression analysis contributed a significant 28% variance in DBP (∆R² = .28, p < .001), with age, being married, BMI, smoking, diabetes, and taking hypertensive drugs significantly contributing to the variance in DBP. Age was a significant predictor of DBP (β = .15, p < .01), indicating that the higher the age, the higher the DBP. Being married (β = .18, p < .0 5) significantly predicted DBP, suggesting that individuals who are married showed significantly higher DBP compared to individuals that are not married. Smoking cigarettes significantly predicted DBP (β = .12, p < .05), indicating that patients who smoke cigarettes had significantly higher DBP compared to non-smokers. Being on hypertensive medication (β = .20, p < .0 1) was a significant predictor of DBP showing that patients on hypertensive medication exhibited significantly higher DBP compared to those that are not. Diabetes was a significant predictor of DBP (β = .12, p < .05), indicating that patients who were diabetic had higher DBP compared to non-diabetic patients.

When the main predictor, anger experience, was entered in Step 2 of the regression analysis, it contributed an additional and significant 4% variance in DBP (∆R² = .04, p < .001) above the contributions of demographic variables and traditional risk factors. As hypothesized, anger experience was a significant and positive predictor of DBP (β = .21, p < .001). This implies that, as anger experience increases, the DBP increases, suggesting that patients high in trait anger were more likely to have increased DBP than patients low in trait anger. Similarly, the results also showed that distress tolerance significantly predicted SBP (β = –.40, p < .001). Distress tolerance contributed an additional and significant 12% variance in DBP (∆R² = .12, p < .001) above the contributions of demographic variables, known risk factors, and anger experience. In addition, when the interaction term was entered in the fourth regression analysis, it contributed a significant variance (∆R² = .01, p < .05) in SBP and was a significant predictor (β = –.09, p < .05) of DBP indicating that distress tolerance was a moderator in anger experience–DBP relationship. The effect of anger experience on DBP depends on an individual’s distress tolerance level.

Similarly, it can be seen from Figure 2 that anger is significantly related to DBP for patients with low distress tolerance compared to patients with high distress tolerance. Specifically, the graph reveals that patients with higher distress tolerance had lower scores on DBP than individuals with low distress tolerance, irrespective of their levels of anger experience.

Figure 2.

Graph showing the moderating role of distress tolerance on the relationship between anger experience and DBP.

Discussion

The study investigated the relationship between anger experience and elevated BP, and the moderating role of distress tolerance on this relationship. As expected, anger experience significantly predicted both SBP and DBP even after we have controlled for the effects of demographic variables and known risk factors for elevated BP. This implies that the higher the anger experience, the higher the elevated BP. This finding is consistent with previous studies (e.g., Hosseini et al., 2011; Schum et al., 2003) that support the idea that anger experience could lead to heightened cardiovascular reactivity which leads to elevated BP. This shows that the link between anger and elevated BP found in other Western cultures is relevant in understanding such phenomena in Nigeria. More specifically, many Nigerians experience challenging and difficult situations that could trigger stress and anger such as unemployment, dwindling income, poor health facilities, and insecurity, among others (Egbue & Nwankwo, 2014; Kayode, Arome, & Anyio, 2014). Moreover, the reported high incidence of hypertension in the country (Akinlua et al., 2015; Ezekwesili et al., 2016) justifies the need to understand the factors that are associated with elevated BP among Nigerians.

The results showed that distress tolerance is significantly related to both SBP and DBP. This demonstrates that an individual’s ability to tolerate distress could be helpful in reducing BP. This finding lends support to previous research that demonstrated that distress tolerance is related with improved psychological wellbeing (O’Cleirigh et al., 2007). It is also consistent with the idea that individuals who experience higher level of psychological distress are more prone to the development of essential hypertension than their counterparts who experience lower levels of psychological distress (Footman et al., 2013). When stress is prolonged, it could lead to an increase in high BP, but the ability to tolerate psychological distress or stress could reduce the incidence of elevated BP among people.

Our finding that distress tolerance moderated the relationship between anger experience and elevated BP suggests that although an individual may be prone to a greater level of anger experience which may increase BP, an ability to withstand and tolerate distress could serve as a moderator in the anger experience–elevated BP relationship. Thus, individuals with high levels of distress tolerance may be more able to respond to negative psychological states and emotions, thereby maintaining high psychological and emotional wellbeing. This finding is consistent with the theoretical assumptions that individuals with a high level of distress tolerance tend to possess generalized perceived capacity to cope with aversive situations as well engage in behaviors that enable them to reduce feelings of distress (Leyro et al., 2010; Zvolensky et al., 2010). The findings also lend support to the activation explanations of the anger–elevated BP relationship. In this sense, distress tolerance acts as a buffer, thereby reducing the individual’s activation levels leading to a reduction in BP. This is also consistent with research findings (e.g., O’Cleirigh et al., 2007; Zvolensky & Otto, 2007) that confirmed that distress tolerance is a moderator or maintenance factor among persons at risk for a variety of psychological disorders.

Our findings could have some important implications for psychological intervention for patients with elevated BP. For instance, the ability of an individual to tolerate psychological distress or discomfort and not trying to escape from it has some adaptive value that is important when experiencing such emotions and can actually result in positive and healthy behavioral change (Leyro et al., 2010). Consequently, studies relating to acceptance and commitment therapy (ACT) have carefully investigated the negative and harmful effects of avoidance and suppression of negative emotional experience and the advantage or usefulness of accepting and experiencing negative emotions (Blackledge & Hayes, 2001). We therefore suggest that such psychological interventions could help patients with elevated BP to successfully tolerate negative emotional distress, thus reducing the degree of anger experience in their day-to-day activities.

Although our study is one of the first attempts at investigating the moderating role of distress tolerance on the relationship between anger experience and elevated BP, there are some limitations worth mentioning. First, we conceptualized distress tolerance as a unidimensional construct. Based on this, we did not capture separately the cognitive and behavioral components of distress tolerance and the relative moderating effects of each of the components on the anger–elevated BP relationship. Scholars (Zvolensky et al., 2010) have maintained that both the perceived capacity to withstand discomfort and the behavioral acts targeted at withstanding distress are important in understanding how distress tolerance relate to desirable outcomes. Future researchers should focus on investigating the predictive power of both cognitive and behavioral components of distress tolerance on elevated BP. Second, the study was carried out in a teaching hospital located in one of the six regions in Nigeria and this may have limited the generalizability of the findings to the entire Nigerian population. Third, the study adopted a cross-sectional design and there is limitation regarding making causal inferences on the relationship between anger arousal and elevated BP. It would be desirable to adopt a longitudinal or experimental design, involving a larger sample from different ethnic groups in Nigeria. These would help in establishing the causal relationship among the variables and ensure generalizability of the findings.

Conclusion

The study investigated the moderating role of distress tolerance in the relationship between anger experiences and elevated BP. Anger experience and distress tolerance were found to be significant predictors of elevated BP. Most importantly, distress tolerance was found to moderate the relationship between anger experience and elevated BP. Since studies have shown that psychological variables are important predictors and moderators of elevated BP as confirmed by this study, the researchers recommend the inclusion of therapies that enhance patients’ coping mechanisms in management of elevated BP.

Footnotes

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

References

Akinlua

J. T.

Meakin

Umar

A. M.

Freemantle

(2015). Current prevalence pattern of hypertension in Nigeria: A systematic review. PLoS ONE, 10, e0140021.

Anderson

C. H.

(1986). Hierarchical moderated regression analysis: A useful tool for retail management decisions. Journal of Retailing, 62, 186–203.

Baron

R. M.

Kenny

D. A

. (1986). The moderator-mediator variable distinction in social psychological research: Conceptual, strategic and statistical considerations. Journal of Personality and Social Psychology, 51, 1173–1182.

Blackledge

J. T.

Hayes

S. C.

(2001). Emotion regulation in acceptance and commitment therapy. Journal of Clinical Psychology, 57, 243–255.

Chobanian

A. V.

Bakris

G. L.

Black

H. R.

Cushman

W. C.

Green

L. A.

Izzo

J. L.

(2003). The seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 report. Journal of the American Medical Association, 289, 2560–2572.

Davids

E. L.

Roman

N. V.

Kerchhoff

L. J.

(2017). Adolescent goals and aspirations in search of psychological well-being: From the perspective of self-determination theory. South African Journal of Psychology, 47, 121–132.

del Barrio

Aluja

Spielberger

. (2004). Anger assessment with the STAXI-CA: Psychometric properties of a new instrument for children and adolescents. Personality and Individual Differences, 37, 227–244.

Devilly

G. J.

(2005). The psychological effects of a lifestyle management course on war veterans and their spouses. Journal of Clinical Psychology, 58, 1119–1134.

Egbue

N. G.

Nwankwo

I. U.

(2014). Insecurity and right to health of Nigerians: Challenges and solutions. European Scientific Journal, 3, 74–82.

10.

Everson

S. A.

Goldberg

D. E.

Kaplan

G. A.

Julkunen

Salonen

J. T.

(1998). Anger expression and incident hypertension. Psychosomatic Medicine, 60, 730–735.

11.

Ewart

C. K.

Elder

G. J.

Smyth

J. M.

Sliwinski

M. J.

Jorgensen

R. S.

(2011). Do agonistic motives matter more than anger? Three studies of cardiovascular risk in adolescents. Health Psychology, 30, 510–524.

12.

Ezekwesili

C. N.

Ononamadu

C. J.

Onyeukwu

O. F.

Mefoh

N. C.

(2016). Epidemiological survey of hypertension in Anambra state, Nigeria. Nigeria Journal of Clinical Practice, 19, 659–667.

13.

Footman

Roberts

Tumanov

McKee

(2013). The comorbidity of hypertension and psychological distress: A study of nine countries in the former Soviet Union. Journal of Public Health, 35, 548–557.

14.

Forouzanfar

M. H.

Liu

Roth

G. A.

Biryukov

Marczak

. . . Ali

(2017). Global burden of hypertension and systolic blood pressure of at least 110 to 115 mm Hg, 1990–2015. Journal of American Medical Association, 317, 165–182.

15.

Gasperin

Netuveli

Dias-da-Costa

J. S.

Pattussi

M. P.

(2009). Effect of psychological stress on blood pressure increase: A meta-analysis of cohort studies. Cadernos De Saude Publica, 25, 715–726.

16.

Harburg

Gleiberman

Russell

Cooper

M. L.

(1991). Anger-coping styles and blood pressure in black and white males: Buffalo, New York. Psychosomatic Medicine, 53, 153–164.

17.

Hayes

S. C.

Wilson

K. G.

Gifford

E. V.

Follette

V. M.

Strosahl

(1996). Experimental avoidance and behavioral disorders: A functional dimensional approach to diagnosis and treatment. Journal of Consulting and Clinical Psychology, 64, 1152–1168.

18.

Hogan

B. E.

Linden

(2004). Anger response styles and blood pressure: At least don’t ruminate about it! Annals of Behavioral Medicine, 27, 38–49.

19.

Hosseini

S. H.

Mokhberi

Mohammadpour

R. A.

Mehrabianfard

Lashak

N. B.

(2011). Anger expression and suppression among patients with essential hypertension. International Journal of Psychiatry in Clinical Practice, 15, 214–218.

20.

Jorgensen

R. S.

Johnson

B. T.

Kolodziej

M. E.

Schreer

G. E.

(1996). Elevated blood pressure and personality: A meta-analytic review. Psychological Bulletin, 120, 293–320.

21.

Julius

Johnson

E. H.

(1985). Stress, autonomic hyperactivity and essential hypertension: An enigma. Journal of Hypertension, 3, 511–518.

22.

Kayode

Arome

Anyio

S. F.

(2014). The rising rate of unemployment in Nigeria: The socio-economic and political implications. Global Business and Economics Research Journal, 3, 68–89.

23.

Khakurel

Agrawal

R. K.

Hada

(2009). Pattern of end stage renal disease in a tertiary care center. Journal of Nepal Medical Association, 48, 126–130.

24.

Koball

A. M.

Himes

S. M.

Sim

Clark

M. M.

Collazo-Clavell

M. L.

Mundi

. . . Grothe

K. B.

(2015). Distress tolerance and psychological comorbidity in patients seeking bariatric surgery. Obesity Surgery, 26, 1559–1564.

25.

Kretchy

I. A.

Owusu-Daaku

F. T.

Danquah

S. A.

(2014). Mental health in hypertension: Assessing symptoms of anxiety, depression and stress on anti-hypertensive medication adherence. International Journal of Mental Health Systems, 8(1), 25. doi:10.1186/1752-4458-8-25

26.

Leyro

T. M.

Zvolensky

M. J.

Bernstein

(2010). Distress tolerance and psychopathological symptoms and disorders: A review of the empirical literature among adults. Psychological Bulletin, 136, 576–600.

27.

Lyness

S. A.

(1993). Predictors of differences between type A and B individuals in heart rate and blood pressure reactivity. Psychological Bulletin, 114, 266–295.

28.

Meckelmann

Pfeifer

Rauh

(2013). Family relationships in childhood, pubertal timing, and subsequent reproductive strategies among adolescents. South African Journal of Psychology, 43, 22–33.

29.

Mozaffarian

Benjamin

E. S.

A. S.

Arnett

D. K.

Blaha

M. S.

Gushman

Huffman

M. D.

(2015). Heart Disease and Stroke Statistics—2015 update: A report from the American Heart Association. Circulation, 131(4), e29–e322.

30.

Novaco

R. W.

(1975). Anger control: The development of an experimental treatment. Lexington, KY: Lexington.

31.

O’Cleirigh

Ironson

Smits

J. A.

(2007). Does distress tolerance moderate the impact of major life events on psychosocial variables and behaviors important in the management of HIV? Behaviour Therapy, 38, 314–323.

32.

Sahraian

Mokhtari

Moaref

Rezaee

Moghimi

Mani

(2015). Hypertensive patients and normotensive individuals: Differences in anger inventory. International Cardiovascular Research Journal, 9, 216–219.

33.

Schneider

R. H.

Egan

B. M.

Johnson

E. H.

Drobny

Julius

(1986). Anger and anxiety in borderline hypertension. Psychosomatic Medicine, 48, 242–248.

34.

Schum

J. L.

Jorgensen

R. S.

Verhaeghen

Sauro

Thibodeau

(2003). Trait anger, anger expression, and ambulatory blood pressure: A meta-analytic review. Journal of Behavioral Medicine, 26, 395–415.

35.

Simons

J. S.

Gaher

R. M.

(2005). The Distress Tolerance Scale: Development and validation of a self-report measure. Motivation and Emotion, 29, 2–20.

36.

Smith

T. W.

(1992). Hostility and health: Current status of a psychosomatic hypothesis. Health Psychology, 11, 139–150.

37.

Spielberger

C. D.

(1988). Professional manual for the State-Trait Anger Expression Inventory (STAXI). Odessa, FL: Psychological Assessment Resources.

38.

Suls

Wan

C. K.

Costa

P. T.

(1995). Relationship of trait anger to resting blood pressure: A meta-analysis. Health Psychology, 14, 444–456.

39.

World Health Organization. (2002). The World Health Report: Reducing risks, promoting healthy life. Geneva, Switzerland: Author.

40.

World Health Organization. (2011). Global atlas on cardiovascular disease prevention and control. Geneva, Switzerland: Author.

41.

Zhao

(2012). Prevalence, awareness, treatment, and control of hypertension among herdsmen living at 4,300 m in Tibet. American Journal of Hypertension, 25, 583–589.

42.

Zvolensky

M. J.

Otto

M. W.

(2007). Affective intolerance, sensitivity, and processing: Advances in clinical science introduction. Behaviour Therapy, 38, 228–233.

43.

Zvolensky

M. J.

Vujanovic

A. A.

Bernstein

Leyro

(2010). Distress tolerance: Theory, measurement, and relations to psychopathology. Current Directions in Psychological Science, 19, 406–410.