Abstract
There is some evidence that blood pressure is higher in persons with darker skin tone but the reasons for this remain unclear. When seen in minorities, the positive relationship between darkness of skin and blood pressure invites hypotheses about potential mediators of the relationship. We investigated the relationship in Hispanics of primarily Mexican descent and included measures of hostility, locus of control and perceived racial discrimination hypothesized to mediate higher blood pressure. Regression analysis revealed no relationship between darkness of skin and blood pressure but correlations between hypothesized mediators were significant and explicable. Cynical hostility and external locus of control were positively associated with perceived racial discrimination. We reasoned that the chronic experience of racial discrimination reinforces the perception of discrimination and feeds both external locus of control and cynical hostility despite no corresponding unfavorable effect on blood pressure.
Hypertension or high blood pressure is a powerful risk factor for heart disease and is responsible for extensive morbidity and mortality throughout the world (Centers for Disease Control and Prevention [CDCP], 2008; World Health Organization [WHO], 2011) and African Americans are at a disproportionately higher risk of high blood pressure when compared to the majority population (Medscape, 2011). Interestingly, several studies have found that darker skin tone is related positively to higher blood pressure (Boyle, 1970; Dressler, 1991; Ernst, Jackson, Robertson, Nevels, & Watts, 1997; Harburg, Gleiberman, Roeper, Schork, & Schull, 1978; Murray, 1991). In one study, the phenomenon was even found in Whites (Gleiberman, Harburg, Frone, Russell, & Cooper, 1993).
Hispanic Blacks exhibit higher rates of hypertension when compared to other Hispanics (Borrell, 2006). The mechanisms accounting for the relationship between skin tone and blood pressure are not entirely clear but Borrell (2006) suggested that racial discrimination may play a role and that Hispanic Blacks, like Blacks, could be treated more unjustly due to their skin tone. Similar results have been found in other studies with darker skinned Hispanics more likely to experience discrimination than their lighter skinned counterparts (Arce, Murguia, & Frisbie, 1987; Codina & Montalvo, 1994). Moreover, it is well-known that Hispanics and African Americans are subjected to similar discriminatory experiences (Fisher, Wallace, & Fenton, 2000; Roberts, Swanson, & Murphy, 2004).
Studies addressing the relationship between skin tone and blood pressure in Hispanics have focused on Hispanics of Puerto Rican descent. In one of these studies, skin tone was not associated with blood pressure but socioeconomic status (SES) was shown to influence this relationship (Gravlee & Dressler, 2005). An earlier study showed a weak but significant relationship between skin color and blood pressure (Costas, Garcia-Palmieri, Sorlie, & Hertzmark, 1981), while a later study found that dark-skinned Hispanics had a much higher risk for developing left ventricular hypertrophy (Sorlie, Garcia-Palmieri, & Costas, 1988), which is often a result of chronic uncontrolled or poorly controlled hypertension.
The relationship between skin tone and blood pressure is likely a complex one. If, however, darker skin tone elicits more discriminatory reactions then a higher level of perceived racial discrimination is likely to be one mediator of higher blood pressure. It is reasonable to argue that recipients of frequent discriminatory provocations are more likely to experience chronic reactions of anger elevating trait levels of hostility. High levels of anger and hostility are associated with higher blood pressures (Ernst, Francis, & Enwonwu, 1990), more hypertension (Routledge & McFetridge-Durdle, 2007), and even higher levels of coronary heart disease (Chida & Steptoe, 2009).
The present study was performed to investigate the relationship of skin tone to blood pressure in Hispanics of primarily Mexican descent while measuring the hypothesized mediators, perceived discrimination, locus of control, and hostility. To our knowledge, neither the relationship nor the possible mediators of the relationship between skin tone and blood pressure have been studied in this population. We hypothesized that the positive relationship between darker skin tone and blood pressure would be replicated in this population and that darker skinned subjects would reveal higher levels of perceived racial discrimination, a more external perceived locus of control, and trait hostility.
Method
Participants
Subjects were recruited from a university student population of primarily Mexican Americans. Following review and approval by the university’s IRB, 144 subjects were recruited from undergraduate classes in which extra credit was awarded for research participation. The sample included 111 females and 33 males whose mean age ± SEM of the sample was 24.05 ± 0.47.
Measures
Questionnaires were used to obtain three of the measures employed in the study. Rotter’s Internality-Externality (I-E) Locus of Control Scale (Rotter, 1966) measures the extent to which a person believes life events to be relatively a product of one’s own control. A high score reveals a belief that life’s events are primarily determined by forces outside the control of the individual (externality). The second measure, the Schedule of Racist Events (Landrine & Klonoff, 1996) measured the perception of diverse racial discriminatory experiences and was modified slightly to apply to Hispanics. Each item is answered three times to assess different racist discriminatory occurrences: (1) recently, (2) during one’s entire life span, and (3) to estimate how stressful the occurrence was perceived to be. The three responses to each item create three subscales: Recent Racist Events (RRE), Lifetime Racist Events (LRE) and Appraised Racist Events (ARE). Hostility was measured using the Cook-Medley HO scale (C-M Ho) of the Minnesota Multiphasic Personality Inventory (MMPI: Hathaway & McKinley, 1940). This scale is frequently employed in studies of cardiovascular and other health outcomes (Chida & Steptoe, 2009; Miller, Smith, Turner, Guijarro, & Hallet, 1996).
Skin tone was assessed with The Pocket Detective 2.1 All Window F & R Reflectance/Tint Meter. This instrument bounces a light off of a selected surface, in this case, the skin, and reveals a digitized quantity of light reflecting back from the surface. Pilot work with the instrument revealed good variation with observable differences in skin tone.
Blood pressure (systolic, diastolic, and mean arterial) and heart rate were monitored with an automated blood pressure device (Dinamap, model No. 1846 SX-P, Kriticon, Inc, Tampa, Fla) commonly employed in cardiovascular research. The instrument uses an oscillometric method for the determination of blood pressure and has an output terminal designed to interface with a personal computer for capturing and storing data.
Procedure
Prior to data collection, participants read and signed a consent form. A measure of skin tone was obtained from the inside of the upper arm, followed by a reading of blood pressure. A cuff was situated over the upper right arm. The blood pressure acquisition device was triggered to obtain systolic and diastolic blood pressures, mean arterial blood pressure, and heart rate. Subjects were then seated at a desk where she or he completed a demographics form and the questionnaires described above. Data were then entered into a database using Statistica 9.0 software (Statsoft, Inc., Tulsa, OK) and correlational statistics were performed to determine the direction and strength of the relationships between variables that were measured.
Results
Multiple regression analyses were performed using skin tone, perceived racism, locus of control, and hostility as predictors of systolic and diastolic blood pressures. Multiple R2 for each blood pressure were small and nonsignificant (+0.04 and +0.06) and none of the individual Betas reached statistical significance for either blood pressure (Range: 0.02-0.19).
Correlational analyses were therefore performed on relationships between what were hypothesized to be variables mediating the expected relationship between skin tone and blood pressure. These analyses revealed statistically significant positive relationships between perceived racial discrimination (all three measures: RRE, LRE, and ARE), locus of control (LOC), and hostility (C-M Ho). Table 1 lists Pearson-Product correlation coefficients and corresponding p levels for these variables. Not unexpectedly, the subscales of perceived racism intercorrelated significantly. Each of the perceived racism subscales correlated significantly with both locus of control and hostility revealing strong positive relationships between these variables.
Pearson Product-Moment Correlation Coefficients for Relationships between Predictor Variables
Note. RRE = recent racist events; LRE = lifetime racist events; ARE = appraised racist events; LOC = locus of control; C-M Ho = Cook-Medley Hostility.
p < .05.
Discussion
The findings did not support the primary hypothesis of the present investigation that darkness of skin is positively related to blood pressure but this relationship has received inconsistent support in the literature and the present finding further weakens confidence that any relationship between skin tone and blood pressure exists. It may well be that darkness of skin has only an artifactual relationship with blood pressure, as has been found in at least one study (Ernst et al., 1997) and is further supported by our understanding of gender-related skin tone differences. Males typically reveal darker skin tone (Boyle, 1970; Ernst et al., 1997; Gleiberman et al., 1993; Harburg et al., 1978; Jablonski & Chaplin, 2000; Klonoff & Landrine, 2000) and this is thought to be related to the influence of testosterone on melanin (Thornhill & Gangestad, 2008). Although there were not statistically significant differences in skin tone between males and females in the present study, t(142) = 0.452, p > .05, the sample of the present study was predominately female (77%) and this may have affected the power of the gender analysis. However, the present investigation did reveal interesting relationships between mediating or predictor variables hypothesized to explain a positive relationship between darkness of skin and blood pressure if it were to have been found.
Indeed the interesting findings of this investigation concerning the relationships between perceived racial discrimination, locus of control, and C-M Hostility are not inexplicable. All of these relationships were positive and received strong statistical support in the present investigation. A plausible explanation of the positive relationship can be found in an understanding of the likely sequence through which each factor might occur. Racial discrimination is a negative social experience that is likely to affect cognitive and emotional systems in a negative way. Certainly, it is not difficult to understand why a person experiencing frequent and chronic racial discrimination would acquire a more external locus of control. The more one is on the defensive in social interaction, the more that person is likely to feel as if he is “reacting” rather than “proacting.” As this process becomes more chronic, the external locus of control trait is likely to become more fixed and stabilized.
A similar effect can be expected in the relationship between perceived racial discrimination and hostility, especially the kind of hostility that is tapped by the C-M Hostility subscale of the MMPI. This measure of hostility has been characterized as “cynical hostility” and shares items on the MMPI with the clinical scale, “Paranoia.” Clearly, as a person adopts an external locus of control focus in life and has experienced frequent and chronic racial discrimination, trust in people erodes. At the very least, a person is more likely to become cynical about the intentions of others and, depending on other related experiences, could eventually distrust people in general. The definitional basis of paranoia, however, would never be established in someone who, in fact, experiences chronic social mistreatment.
The finding of a relationship between perceived racial discrimination and external locus of control in Hispanics extends our understanding of this phenomenon in racial minorities. This finding improves our understanding of the psychological plight of minorities who experience chronic discrimination. Stabilization of external locus of control might eventually result in helplessness, which has a well-documented relationship with depression and substance abuse, the latter of which is seen in disproportionately higher frequency among Hispanics (Lowinson, Ruiz, Millman, & Langrod, 2004; National Institute on Drug Abuse, 2007).
In future investigations, sampling might include significantly more males to balance the study by gender and perhaps a greater range of age and socioeconomic groups. This sample was exclusively college students and it is well-known that this young and well-educated type of sample compromises the external validity (generalizability) of findings.
Footnotes
This study was performed in partial fulfillment of the master of arts degree in clinical psychology at the University of Texas–Pan American.
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
The author(s) received no financial support for the research, authorship, and/or publication of this article.