Physiological stress response of young adults exposed to bullying during adolescence
Introduction
Peer victimization is a common experience among children across the world [1]. In North America, surveys estimate that approximately 10–15% of children are subjected to chronic bullying in school [2], [3], [4]. Severe, chronic exposure to bullying has been shown to be associated with psychological problems, such as low self-esteem, anxiety, and depression [2], [5], [6], [7], [8]. However, little attention has been paid to the physiological manifestations of the emotional disruptions caused by this victimization. It is likely that physiological disruptions associated with depression or posttraumatic stress disorder (PTSD) would be apparent in victims of chronic bullying. Frequent bullying is a chronic social stressor, and as such, should be associated with physiological consequences predicted by animal models of social stress [9], [10].
The disruptive effect of chronic stress on the hypothalamic–pituitary–adrenal (HPA) axis has been demonstrated repeatedly in both animals and humans. The direction of this disruption, however, depends on a variety of factors. Animal studies of social stress and learned helplessness mostly show evidence for basal hypercortisolism and blunted HPA responses to stress in socially defeated subjects [11], [12], [13], [14], [15], [16]. Most animal studies have been done on males, but there are sex differences in the physiological response to chronic stress in rats [17] and hamsters [18], such that females are more resilient to the negative effects of stress. It appears that estradiol has a protective effect against stress [17], [18]. In addition to HPA axis disruptions, cardiovascular reactions are also altered in response to social stress, resulting, for example, in heart beat aberrations and increased heart rate [19]. In summary, chronic exposure to social stress and defeat is associated with an alteration in HPA activity, and cardiovascular abnormalities in socially defeated rodents [20].
In humans, chronic stress can lead to anxiety disorders, depression, and in extreme cases, PTSD. In general, the psychological problems that stem from chronic stress have been associated with both disruptions of circadian cortisol rhythms and altered basal levels of cortisol [21], [22], [23], [24]. Similar disruptions have been found in the cortisol reactivity to acute stress of participants who have been exposed to chronic stress [25], [26], [27]. Adults bullied at work [28] and frequently bullied children [29] show lower levels of cortisol across the day compared to non-bullied controls. An additional study of children exposed to violence also found that when shown a video clip relevant to violence they have experienced, peer victimization was related to increased cortisol responses to the video stressor [30]. The direction of the change in cortisol activity (either basal levels or acute reactivity) due to chronic stress is unclear as several studies have shown a change in each direction.
A recent meta-analysis provides a summary of the complexity of the relationship between chronic stress and HPA response and the factors that influence it [31]. Related to bullying, the researchers found that if the chronic stress was social in nature, daytime cortisol was higher, if the stressor was perceived as uncontrollable, the daily cortisol cycle was flattened and high, and people with PTSD had lower cortisol across the day. In relation to reactivity, they found that while most studies showed suppressed cortisol levels in response to the dexamethasone suppression test, depressed people showed much higher levels of cortisol after the test, suggesting they were less sensitive to external influences affecting the HPA axis. One of the biggest factors was the time that had lapsed since the cessation of the chronic stressor. Immediately after the stressor, most people showed elevated cortisol, while after time, cortisol levels rebounded to hypocortisolemic levels.
A recent review of sex differences in stress responsiveness in healthy men and women showed that on average, men's cortisol and blood pressure responses to stress were more pronounced, while women showed greater heart rate response than men [32]. Based on this type of data, it is likely that there are sex differences in physiological responses to stress, but the direction of difference may depend on the variable being measured.
As for the sympathetic responses of chronically stressed people, an abundance of evidence in recent years links chronic stress to cardiovascular variables [33]. A review of 19 studies found that some studies report heightened reactivity to acute stressors in participants who experienced chronic stress, and some studies report a suppressed cardiovascular response in chronically stressed participants [34]. Stressed participants showed delayed cardiovascular recovery in the majority of studies reviewed. Similar to the cortisol data in humans, it seems that chronically stressed participants have different levels of reactivity to acute stress compared to controls, but the direction of the difference varies.
The present study examined responses to an acute stressor among participants with and without a history of bullying, a chronic social stressor. Based on past research in animals and humans, we hypothesized that participants with a history of being frequently bullied would respond differently to an acute stressor than those who have never been bullied. We also expected there would be sex differences in participants' physiological responses to stress.
Section snippets
Participants
Participants were undergraduate students recruited through an introductory psychology research pool who received partial class credit for their participation. At the beginning of the semester, all introductory psychology students completed a large online survey composed of screening questionnaires for numerous studies. In the screening survey, we included a brief questionnaire that asked participants the frequency with which they had been bullied in high school, junior high, and elementary
Preliminary analyses
To ensure results were not influenced by weight, we compared BMI values between groups. Participants in the Bullied and Non-Bullied groups had similar BMIs, all within the healthy range. For women, the mean BMI for the Non-bullied group was 21.5 ± 2.7 and for the Bullied group it was 22.9 ± 4.4. These differences were not significantly different [t(36) = − .89, p = .38]. For men, the mean BMI for the Non-bullied group was 23.1 ± 2.4 and 22.8 ± 3.4 for the Bullied group, which was not significantly different
Discussion
In the present study, we found that blood pressure responses to acute stress in Bullied men were blunted compared to Non-bullied men, while heart rate and cortisol responses were not different between the two groups. There was a difference in responses between males who reported lingering anger over their bullying experiences and males who did not report any anger. In women, there were no differences in the cardiovascular or cortisol responses of Bullied and Non-bullied participants. Salivary
Acknowledgments
We are grateful to Ragini Yallampalli, Ashley Garner, Luke Thorstenson, Megan Rooney, Katie Ryan, and Hetal Ghadia, for their assistance with data collection and entry. The studies were conducted under the support of grant IOB0518272 from the NSF to YD and NIH training grant MH65728-2 to MLN. CD is supported by a predoctoral fellowship from the John A. Hartford Foundation's Building Academic Geriatric Nursing Capacity.
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