Effects of personality stress and lifestyle on hypertension: An Australian twin study

Transcription

1 Bond University Humanities & Social Sciences papers Faculty of Humanities and Social Sciences Effects of personality stress and lifestyle on hypertension: An Australian twin study Victor Mellors University of Queensland Gregory J. Boyle Bond University, Len Roberts Queensland Institute of Medical Research Follow this and additional works at: Part of the Health Psychology Commons Recommended Citation Victor Mellors, Gregory J. Boyle, and Len Roberts. (1994) "Effects of personality stress and lifestyle on hypertension: An Australian twin study" Personality and Individual Differences, 16 (6), : ISSN This Journal Article is brought to you by the Faculty of Humanities and Social Sciences at It has been accepted for inclusion in Humanities & Social Sciences papers by an authorized administrator of For more information, please contact Bond University's Repository Coordinator.

2 1 Effects of Personality, Stress and Lifestyle on Hypertension: An Australian Twin Study Victor Mellors University of Queensland Gregory J. Boyle University of Queensland and Bond University and Len Roberts Queensland Institute of Medical Research

3 2 Abstract This study investigated the association of personality, stress and lifestyle with self-reported hypertension (validated by actual use of antihypertensive medication, and separately by cross-twin reporting). Subjects were 4870 female and 2746 male twins from the Australian Twin Registry. Personality and stress variables were measured by the Eysenck Personality Questionnaire and the Delusions-Symptoms-States Inventory. Alcohol intake, cigarette consumption and monthly exercise activity represented lifestyle variables. Hypothesis 1 predicted that predominant personality types among hypertensives are neurotic introverts and extraverts low on psychoticism; Hypothesis 2 predicted that personality and stress are better predictors than lifestyle variables in the genesis of hypertension; Hypothesis 3 predicted that these variables act synergistically. Results showed that neurotic introverts and extraverts low on psychoticism. and high on the Lie scale were prevalent among male hypertensives, while in female hypertensives neurotic introverts low on psychoticism, and high on the Lie scale predominated. Across gender, lifestyle variables were the best predictors. In accord with Hypothesis 3, effects on hypertension were magnified when personality, stress and lifestyle variables acted synergistically.

4 3 Introduction This study examines the role of personality, stress and lifestyle on hypertension, as indexed by self-report, usage of antihypertensive medication, and cross-twin reporting. Personality and stress factors are considered, and Eysenck's (1991) personality types are related to hypertension, through negative and positive affect with stress. The interaction of personality with various lifestyle habits such as drinking, smoking and exercise which affect hypertension is also discussed. Hypertension is a chronic sustained elevation of blood pressure, either primary or secondary in nature. Primary ("essential") hypertension has no identifiable physical cause (Phillips, 1991). Secondary hypertension may result from a specific physical cause such as renal failure, adrenal tumour or aortic disease (O'Brien & O'Malley, 1982). Personality and stress form a complex causal chain in the genesis of heart disease. These factors have both additive and synergistic effects (Grossarth-Maticek & Eysenck, 1992). Personality and stress may have similar effects on hypertension (Russo & Zuckerman, 1992). Stress-related processes may be involved in the initiation of disease, and commonly they affect the course, severity and prognosis, depending on personality differences (Krohne, 1990; Schmitz, 1992; Strelau, 1988). Stress has been associated with increased susceptibility to infectious disease, occurrence of immune-related disorders, peptic ulcers, coronary heart disease and hypertension (Lobel & Dunkel-Schetter, 1990; Steptoe, 1991). The present study investigates stress-related negative mood states. Neurotic introverts and extraverts low on psychoticism (P), as measured via the Eysenck Personality Questionnaire (EPQ; Eysenck & Eysenck, 1975), appear to have an

5 4 inability to cope with anger, which in turn, may be related to hypertension (Kirkcaldy & Furnham, 1991; Zuckerman, 1988; Eysenck, 1991). The combination of mood variability, and heavy alcohol and cigarette consumption may elicit a synergistic effect with these personality types and result in hypertension. Unlike their high P counterparts, neurotic introverts and extraverts low on P do not exhibit the associated traits of high sensation-seeking and impulsivity which are related to lower blood pressure levels (Zuckerman, 1988, 1991). When under stress, and with heavy alcohol consumption, the neurotic introvert and extravert low on P are more susceptible to hypertension. It is postulated (Hypothesis 1) that the two most predominant personality structures among hypertensives are those of the neurotic introvert and extravert low on P; (Hypothesis 2) that personality variables and stress are significantly better predictors of hypertension than lifestyle variables such as drinking, exercise and smoking; and (Hypothesis 3) that personality, stress, drinking, smoking and exercise act synergistically in the genesis of hypertension.

6 5 Method Subjects The study involved 3808 pairs of monozygotic and dizygotic twins listed on the Australian NH & MRC Twin Registry. The twin structure of the data has been explored in the present analysis, as there were 4870 female and 2746 male twins, ranging in age from years. The mean age for males was 34.5 years and for females 34.4 years (Table 1). Between November 1980 and March 1982 each twin had completed a self-report mailed questionnaire on psychological lifestyle, health and demographic information (education, religion, occupation). Data for age, personality, stress, lifestyle and hypertension was also collected. Personality and stress data was obtained from psychometric tests. Data for lifestyle variables was based on self-reported exercise activity, smoking and alcohol consumption. Instruments The EPQ measures personality dimensions of Extraversion (E), Psychoticism (P), Neuroticism (N) and includes a Lie (L) scale. This personality instrument is reasonably reliable and valid (Eysenck, 1991). The Delusions- Symptoms-States Inventory or DSSI (Foulds & Bedford, 1975) measures the mood states of anxiety and depression used as stress measures in the present study. The scales are purportedly indices of "state" rather than "trait" characteristics (Eaves, Eysenck & Martin, 1989). In a subsample of 96 twins from this experimental data, two (DSSI) questionnaires were sent out at an interval of 3 months. The mean correlation between the twins' scores on the individual items

7 6 was Reliabilities of the 7-item anxiety and depression scales, however were both about 0.6 (Eaves et al., 1989). Foulds and Bedford found the DSSI to be a reliable instrument for measuring mood states of depression and anxiety. For the EPQ personality variables, each S obtained a score out of 21 for E, 23 for N, 25 for P and 21 for the L scale. For the stress variables, each twin obtained a score out of 21 for anxiety and for depression (DSSI). There were 7 items for each mood state and they were scored on a 4 point scale with 0 representing not at all; 1, a little; 2, a lot; 3, unbearably. For alcohol consumption, a score was calculated from the amount of alcohol consumed on weekends and weekdays. For cigarettes, consumption involved what each individual smoked per day. For exercise, individuals were scored on a 1-5 scale with 1 representing jogging, cycling or any vigorous sport 3-4 times a week, 2 representing sport or exercise twice a week, 3 representing exercise such as tennis or golf once a week, 4 representing 2-3 times a month of regular light exercise (e.g. gardening), and 5 representing no exercise at all. Ss were asked whether they had previously suffered from hypertension. This question aimed to ascertain whether or not Ss had previously been diagnosed medically as having high blood pressure/hypertension. The Hypertension variable was represented by answering "Yes" or "No" and was coded 1 or 0 from the questionnaire. The study specifically took advantage of the cross-reporting by the co-twin, as well as taking into account actual use of antihypertensive medication.

8 7 Table 2 Breakdown of self-reported hypertension Age Number % Total N= 375. Procedure After personality, stress and lifestyle variables were established, a statistical model was formed to test the hypotheses (HI, H2 and H3, respectively). Samples were drawn for hypertensive and non-hypertensive groups. For HI, personality type by hypertension level represented the independent variable while frequency of personality type for hypertension and non-hypertension level represented the dependent variable. In regard to H2, the dependent variables of personality, stress and lifestyle were used to discriminate hypertensives from nonhypertensives. Finally, for H3, the same procedure was employed and interactions between discriminating variables were analysed.

9 8 Results There were two modes of validation available in relation to individuals identified as being hypertensive. One method was to examine the relationship between self-reported hypertension and actual use of antihypertensive medication. The second approach was to use the cross-twin reporting as a check on reliability. The first method revealed that approx. 40% of those identified as being hypertensive were actually taking antihypertensive medication. This is slightly lower than the findings of the I989 National Heart Foundation Risk Factor Prevalence Study in Australia, which found that as a proportion of all hypertensives, 47% of men, and 23% of women were not on antihypertensive medication. However, if a relatively young person was diagnosed as being borderline hypertensive (diastolic blood pressure of around 95 mm Hg), other forms of remedy might be recommended (e.g. exercise, low-salt diet, cessation of alcohol intake) rather than antihypertensive medication. From Table 2, it can be seen that 155 hypertensive individuals (41%) of the hypertensives were in young age categories between 20 and 39 years. This could account for the moderate relationship between antihypertensive medication use and those identified as being hypertensive. Of those taking medication, the majority were in the older age categories. However, whether they were borderline hypertensive or not is another question. Tetrachoric and biserial analyses resulted in a 0.91 correlation between self-reported hypertension and use of antihypertensive medication, and a 0.42 correlation between self-reported hypertension and increasing age. A bivariate path-analytic model was fitted using MX (see Fig. 1), correcting for age on the assumption above, and including the additive genetic components for each variable. The Akaike Information Criterion or AIC (model

10 9 parsimony) was The chi-square goodness-of-fit test was not significant (χ2) = 5.997, df= 15, suggesting a good fit of the model to the data. The pathanalytic model reveals that approx. 38% of the variance explained for hypertension can be attributed to genetic effects, and 31% to the environment. In regard to the second method of verifying individuals as being hypertensive, the cross-twin reliability check revealed about a 45% agreement between Twin I on Twin 2, and Twin 2 on Twin 1 for hypertension. However, if a person has a diastolic blood pressure of around 95 rom Hg (baseline measure for hypertension), then the symptoms will be minimal, and as a result the individual may not perceive him/herself as being hypertensive, and thus not inform the other twin. Another plausible explanation would be proximity. As most of the twins live a significant distance apart from each other, it may simply be a matter of the twins losing touch with each other and thus not knowing each other's health status. Hl was investigated by calculating means and standard deviations for males and females on E, N, P and L scales (Table 3). Sixteen possible personality types were then generated for each gender along with the frequency of each type for hypertensive and non-hypertensive twins (for male non-hypertensives and hypertensives N = 124and 142, respectively, and for females N = 411 and 455, respectively). The first step involved collapsing the four types of personality structure proposed to predict hypertension. These were neurotic extraverts and introverts low on P, and low on L with stable extraverts and introverts low on P, and high on L. After these personality types were collapsed into non-hypertensives and hypertensives, they were compared with the remaining 12 personality types that had been similarly collapsed into non-hypertensives and hypertensives.

11 10 Fig. I. Path-analytic model of hypertension and medication (geneticenvironmental effects). Hypertension Age I Medication, (Antihypertensive)

12 11 For both males and females, the 16 types were distributed differently for hypertensives and non-hypertensives [females: χ2 (15) = 44.77, P< ; males: χ2 (15) = 26.94, P < 0.05]. Neurotic introverts low on P and high on L were found to be more prone to hypertension among females while stable extraverts/low on P, and low on L were less prone to hypertension. For males, neurotic introverts Table 3 Descriptive statistics of personality. stress and lifestyle variables for males and females. Personality Stress Lifestyle Gender N p E L Anx. Dep. Alcohol Cigs. Exercise Males <N= 1612) M SD !! I.J2 Females <N= 2232> M SD !! N = Neuroticism, P = Psychoticism, E = Extraversion, L = Lie. Anx = Anxiety, Dep =Depression. Alcohol = weekly alcohol consumption, Cigs = daily cigarette consumption. Exercise = 1-5 scale of exercise activity from weekly to monthly. Table 4 Discriminant function analysis on personality. stress and lifestyle variables for male and female hypertensives Correlations of predictor variables with discrimination Univariate Predictor variable function I F(l,6010) (a) Males Exercise Cigarettes Extraversion Neuroticism Anxiety p< (b) Females Univariate F(1.2230) Exercise Anxiety Cigarettes Neuroticism Extraversion

13 12 and extraverts low on P, and high on L were found to be more prone to hypertension. Stable extraverts high on P, and high on L were less prone to hypertension. H2 was investigated using a discriminant function analysis (via SPSSX) across sex. To assess prediction of membership in the two groups (nonhypertensives vs hypertensives), four personality, two stress and three lifestyle predictors were used. For males, 1612 cases were retained (1484 nonhypertensives, 128 hypertensives). For females, 2232 cases were retained (1985 non-hypertensives, 247 hypertensives). For males one discriminant function was calculated with a/ (9) = 90.67, P< , accounting for most of the betweengroup variance. Correlations between predictors and the discriminant function are presented in Table 4(a). The best predictors for distinguishing between male nonhypertensive and hypertensive twins in order were: exercise, cigarettes (lifestyle), E and N and anxiety (stress). The canonical correlations were for nonhypertensives and 0.82 for hypertensives. On the discriminant function, hypertensives scored higher, while non-hypertensives scored at a lower level. These results suggested that lifestyle variables are better predictors of hypertension than personality variables, and do not support H2. For females, one discriminant function was calculated with a l (9) = , P < , accounting for most of the between-group variance. Correlations between predictor variables and the discriminate function are shown in Table 4(b). The best predictors for distinguishing between female nonhypertensive and hypertensive twins in order were: exercise (lifestyle), anxiety (stress), cigarettes (lifestyle), N and E. The cut-off point for significant correlations was The canonical correlations were for non-

14 13 hypertensives and 0.43 for hypertensives. On the discriminant function, hypertensives scored more highly, while non-hypertensives scored at a lower level. These results suggested that personality and stress were not the best predictors and failed to support H2. A discriminant function analysis was calculated for each gender. The analysis compared all possible two-way interactions between all variables. For males, results showed a significant/ (45) = , P < Correlations between predictors and the discriminant function can be seen in Table 5(a). Exercise, cigarettes (lifestyle) and E were the best single predictors that discriminated between non-hypertensive and hypertensive twins. Interactions were found between cigarettes and exercise (lifestyle), N and exercise (personalitylifestyle), L and cigarettes (personality-lifestyle), N and cigarettes (personalitylifestyle), anxiety and cigarettes (stress-lifestyle), Land exercise (personalitylifestyle), anxiety and exercise (stress-lifestyle) E and cigarettes (personalitylifestyle) and N and anxiety (personality-stress). These interactions discriminated best between non-hypertensive and hypertensive twins. The canonical discriminant functions were for non-hypertensives and 0.99 for hypertensives. These results partially support a synergistic effect on hypertension between personality, lifestyle and stress variables, in accord with H3. For the discriminant function analysis on females, results showed a significant χ2 (45) = , p < Correlations between predictors and the discriminant function are in Table 5(b). Exercise, cigarettes (lifestyle) and anxiety (stress) were the best single predictors that discriminated between nonhypertensive and hypertensive twins. Interactions were found between N and exercise (personality-lifestyle). anxiety and exercise (stress-lifestyle), cigarettes

15 14 and exercise (lifestyle). P and cigarettes (personality-lifestyle), N and anxiety (personality-stress), anxiety and cigarettes (stress-lifestyle), L and anxiety (personality-stress). These interactions discriminated best between nonhypertensive and hypertensive twins. The canonical correlations were 0.07 for non-hypertensives and 0.58 for hypertensives. These results partially support a synergistic effect on hypertension between personality, stress and lifestyle variables. Table 5. Discriminant function analysis on main-effects two-way interactions of personality. stress and lifestyle variables for male and female hypertensives and female Predictor variable Correlations of predictor variables with discriminant Univariate function I F(l,l610) P< Cigarettes-exercise Neuroticism-exercise Lie-cigarettes Exercise Cigarettes Neuroticism-cigarettes Anxiety-cigarettes Lie-exercise Anxietyexercise Extraversion ExtrJversion-cigarettcs Neuroticism-anxiety (a) Males (b) Females Univariate F(l,2230) Neuroticism-exercise Exercise Anxiety-exercise Cigarctte:-.-cxerdse Psychoticism-cigarettes Anxiety Lie-exercise Neuroticism-cigarettes Neurnticism-anxietv Cigarettes ' Anxiety-cigarettes Lie-anxiety (){)()() 0.(){)() ()(}()6 0.{)(})) {)())

16 15 Discussion Regarding H1, male hypertensive twins were found to be neurotic introverts or extraverts low on P and high on L scale. High L individuals may be motivated to seek approval. Instead of a candid self-appraisal, they may have an "ideal self concept" that they present to others. This, in combination with high N, may lead to emotional conflict of either suppression or over-expression of anger. the former relating.to introverts, the latter to extraverts. This suggests that high L and N scores might be a problematic combination for hypertension. Alternatively, high L might be related to P, suggesting a relationship between hypertension and the associated high P traits. However, this interpretation is unlikely because research has shown that the high P sensation-seeking trait is not related to hypertension. This immunity of high P to hypertension was partially supported in this study which found stable extraverts (high on P, and high on L) were less prone to hypertension. This may indicate the importance of P in preventing hypertension in males. The high L scale may only be important when combined with N. An extravert with high P and high L, although wanting approval from others, may have the psychological resources to "shrug off' any emotional hurt from these ambitions. High P scorers tend to be cold, unempathic and toughminded people (they have "thick skins"). This might ward off emotional let-downs that may precipitate hypertension. The personality type found in female hypertensive twins was similar to that for males, except that E was not related to hypertension. Neurotic introverts with low P, high L predominated among female hypertensives. This personality type is linked with anger suppression which may result in hypertension. Like males the combination of high N and L may explain this finding. Neurotic introverts are

17 16 traditionally shy, anxious and inhibited people. If they seek total approval and acceptance from significant others and cannot deal with this conflict overtly, this may result in anger suppression and hypertension. The personality type found to be less prone to hypertension among female twins was the stable extravert (low on P, and low on L). Stable extraverts are characterized by positive mood states and high stress tolerance (Williams, 1990). This finding contrasts with the stable extravert (high on P, and high on L) found in male non-hypertensives. P is highly related to aggression, impulsivity and sensation-seeking and Eysenck and Eysenck (1976) describe it as a measure of "maleness." On average, and excluding deviant populations, males score higher than females on the P dimension. This finding infers that females are less aggressive than males so the expression of aggression through sensation-seeking activities may not be as important to females as it is for males. Therefore, women who are stable and extraverted may have a different way of coping with anger other than aggression unlike their male counterparts. Zuckerman (1988) has found that males high in sensation-seeking (linked with high P) will seek activities that will lower catecholamine systems and lower blood pressure. These findings imply that in males, high P and associated traits may have a protective effect in lowering blood pressure. Regarding H2, the best predictors for male hypertensive twins included lower exercise levels, higher cigarette consumption, lower E, higher N, and higher anxiety. These results showed that lifestyle variables were better predictors of hypertension than were personality and stress variables. There was also a weak negative relationship between P and hypertension suggesting that low scorers were susceptible to hypertension. This study suggests that personality and stress are

18 17 linked in the causal chain of hypertension, but are not as important as lifestyle variables. The neurotic introverted person more so than the extraverted one may be more susceptible to hypertension, especially if there is higher cigarette consumption, lower exercise, and higher anxiety. For female hypertensive twins, the best predictors included lower exercise levels, higher anxiety, higher cigarette consumption, higher N and lower E. These results suggest that lifestyle and stress variables were the largest predictors of hypertension. Regarding H3, synergistic effects were found between lifestyle, stress and personality variables for hypertensives. These interactions suggest that although personality variables are not as important at the main effect level, they may be important at the interaction level. Personality variables in interaction with lifestyle and stress variables increased susceptibility to hypertension. For male hypertensives, there were five interactions between lifestyle variables and certain personality components. The most theoretically interpretable interactions that increased hyper tension susceptibility were higher N and lower exercise, higher L and higher cigarettes, higher N and higher cigarettes, lower exercise and higher L, lower E and higher cigarettes. Other inter actions showed similar effects on hypertension such as higher anxiety and higher cigarettes, lower exercise and higher anxiety, higher N and higher anxiety, and higher cigarettes and lower exercise. These interactions suggest the importance of a personality X stress X lifestyle interaction in magnifying susceptibility to hypertension. Exercise may lower anxiety. The more neurotic and anxious individuals are the more they smoke, and this may contribute to hypertension. For the female hypertensives, four personality-lifestyle interactions included higher N and lower exercise, higher P

19 18 and higher cigarettes, higher N and higher cigarettes, and higher L and lower exercise. Other interactions were lower anxiety and higher exercise, higher cigarettes and lower exercise, higher N and higher anxiety, higher cigarettes and higher anxiety, and higher Land higher anxiety. These results partially support H3, that personality, stress, smoking and exercise act synergistically in the genesis of hypertension. Conclusions Personality and stress does appear to play a role in the "causal chain" of hypertension but it does not seem as important as lifestyle variables. Results revealed some interactions between personality, stress and lifestyle variables. These interactions magnified the effect on hypertension suggesting a synergistic relationship. Although the predicted hypertensive personality was not found, exploratory analysis did find predominant personality types among male and female hypertensives. Male hypertensives are characterized by neurotic introverts or extraverts low on P, high on L. Female hypertensives tended to be neurotic introverts low on P, high on L. Despite the lack of support for two of the three research hypotheses, the results did suggest that personality dimensions play a role in the aetiology of hypertension and that they interact with various lifestyle variables. The notion of P protecting individuals from hypertension needs to be further investigated. Another area for future investigation is the question of personality types among hypertensives for different age groups. In conclusion, the present findings suggest that there is a complex "causal chain" in the genesis of hypertension, involving not only physiological, but also psychological variables.

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