Non-suicidal self-injury and life stress: A systematic meta-analysis and theoretical elaboration

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Highlights

  • We conducted a meta-analysis and narrative review of the link between stress and NSSI.

  • A significant but modest relation was found between life stress and NSSI.

  • Cross-sectional design limitations render the temporal nature of the relation unclear.

  • A preliminary conceptual model of this association is presented to guide future study.

Abstract

Recent years have seen a considerable growth of interest in the study of life stress and non-suicidal self-injury (NSSI). The current article presents a systematic review of the empirical literature on this association. In addition to providing a comprehensive meta-analysis, the current article includes a qualitative review of the findings for which there were too few cases (i.e., < 3) for reliable approximations of effect sizes. Across the studies included in the meta-analysis, a significant but modest relation between life stress and NSSI was found (pooled OR = 1.81 [95% CI = 1.49–2.21]). After an adjustment was made for publication bias, the estimated effect size was smaller but still significant (pooled OR = 1.33 [95% CI = 1.08–1.63]). This relation was moderated by sample type, NSSI measure type, and length of period covered by the NSSI measure. The empirical literature is characterized by several methodological limitations, particularly the frequent use of cross-sectional analyses involving temporal overlap between assessments of life stress and NSSI, leaving unclear the precise nature of the relation between these two phenomena (e.g., whether life stress may be a cause, concomitant, or consequence of NSSI). Theoretically informed research utilizing multi-wave designs, assessing life stress and NSSI over relatively brief intervals, and featuring interview-based assessments of these constructs holds promise for advancing our understanding of their relation. The current review concludes with a theoretical elaboration of the association between NSSI and life stress, with the aim of providing a conceptual framework to guide future study in this area.

Introduction

Life stress has been identified as a non-specific risk factor for psychiatric illness. It figures prominently in etiological models of a variety of mental disorders, including schizophrenia (Walker, Mittal, & Tessner, 2008), substance use (Sinha, 2001), depression (Monroe & Harkness, 2005), and, of course, post-traumatic stress disorder (Brewin & Holmes, 2003). Consistent with several of these theoretical perspectives, life stress has been found to be associated with increased risk for psychosis (Beards et al., 2013), substance use and dependence (Enoch, 2011, Hyman and Sinha, 2009), and depression (Hammen, 2005).

Stressful life events have also been theoretically and empirically linked with risk for self-harm, particularly in the form of suicidal ideation and behavior (Liu and Miller, 2014, Mann et al., 2005). Considerably less studied in this regard is non-suicidal self-injury (NSSI), defined as the direct and deliberate destruction of one's own bodily tissue in the absence of any suicidal intent (Nock, 2010). Although it has traditionally received less empirical consideration than suicidal behavior, NSSI has been increasingly recognized over the last decade as an important and phenomenologically distinct clinical phenomenon in its own right (Muehlenkamp, 2005). Indeed, NSSI as a distinct syndrome has been included in DSM-5 as a disorder warranting further study (American Psychiatric Association, 2013). The relative neglect of NSSI in earlier clinical research stemmed, in large measure, from the view that it exists along with suicidal behavior on a continuum of deliberate self-harm, and, moreover, that it falls on the milder end of this spectrum (Brent, 2011a). There is emerging evidence, however, suggesting that this is not the case. That is, although NSSI and suicidal behavior do share some common correlates, they differ significantly in their functions, neurobiology, response to treatment, and long-term trajectory (Brent, 2011a, Mars et al., 2014, Muehlenkamp, 2005, Muehlenkamp and Gutierrez, 2007, Wichstrøm, 2009). Not only is NSSI a meaningfully distinct form of self-harm, there is some emerging evidence to indicate that it may be an even stronger predictor of suicidal behavior than a prior history of suicide attempts (Asarnow et al., 2011, Wilkinson et al., 2011), highlighting the clinical importance of this behavioral phenomenon.

Several researchers have emphasized the need for studies of suicide to move beyond the identification of general risk factors toward elucidating causal elements that lead individuals to engage in this specific form of self-harm, so as to inform intervention and treatment strategies (Brent, 2011b, Nock, 2009a). Given the current paucity of evidence-based treatments for NSSI (Whitlock, 2010), especially in adolescents (Nock, 2012), the need for research uncovering causal factors for this behavior also holds true. Arriving at a better understanding of the relation between life stress and NSSI may be particularly important in this regard. Specifically, insofar as stressful life events are a temporally delimited rather than trait-like risk factor, and, moreover, insofar as these stressful life events potentially precipitate occurrences of NSSI, documenting this relation may aid in advancing our conceptualization of who is generally at risk to include when they are at imminent risk for engaging in this behavior. Such knowledge is of potential clinical utility in formulating and timing intervention strategies, particularly with chronically high-risk individuals.

The principal aim of the present article was to present a systematic meta-analysis of the empirical literature on the association between life stress and NSSI. As our interest was in conducting a comprehensive review of the literature, our meta-analysis was supplemented by a qualitative review of findings for which there were too few cases (i.e., < 3) for reliable approximations of effect sizes. To provide an appropriate context in which to evaluate the existing literature, we first began with a brief overview of the conceptualization and measurement of life stress. We then proceeded with a consideration of the relevance of life stress to conceptual models of NSSI. Following a comprehensive review of the current literature on life stress and NSSI, we ended with a discussion of methodological considerations and a theoretical elaboration of the relation between these two constructs, with the aim of providing a framework to guide future study in this area.

As a risk factor for negative mental health outcomes, stress has been defined and studied in a variety of notably different ways (for a detailed review, see Cohen, Kessler, & Gordon, 1995). These include physiologic stress, especially as operationalized in terms of hypothalamic-pituitary-adrenal (HPA) axis reactivity and allostatic load (McEwen, 1998, Selye, 1936). A second frequently adopted approach to conceptualizing stress centers on psychological or subjective stress (e.g., degree of distress experienced as a result of the individual's cognitive appraisal of the threat or challenge posed by an event; Lazarus & Folkman, 1984). In contrast, the focus of yet another commonly observed perspective is on exposure to exogenous stimuli or events within the individual's environment (e.g., loss of a job, end of a friendship), independent of the individual's subjective interpretation of the events (Grant et al., 2004, Hammen, 2005).

Although studies of physiologic and subjective stress have contributed considerably to our understanding of risk for different forms of psychopathology (Gunnar and Quevedo, 2007, Park, 2010), the current review focuses exclusively on stress as defined within the third tradition, often termed “objective” stress (Hammen, 2005). Several researchers have commented on the existence of certain significant advantages of this conceptualization of “objective” stress relative to subjective stress (Grant et al., 2003, Hammen, 2005). In particular, a potential concern with operationalizing stress based on subjective or cognitive appraisals of the stressfulness of an event is that it risks confounding environmental events with the individual's underlying diathesis. That is, measures based on self-report of the perceived stressfulness of experienced life events, to varying degrees, reflect both objectively occurring life events and pre-existing vulnerabilities (e.g., cognitive traits or biological propensities), with the latter accounting for individual variability in subjective stress ratings of the same life event. Support for this view may be found in several cognitive theories of mental illness. For example, within the depression literature, negative cognitive appraisals of life events have been hypothesized to lead to greater experiences of distress (Abramson, Metalsky, & Alloy, 1989). Empirical support for the potential influence of individual diatheses on subjective appraisals of life stress is also evident in studies observing subjective ratings of life event severity and their association with neuroticism (Espejo et al., 2011), and a polymorphism in the promoter region of the serotonin transporter gene (Conway et al., 2012). Moreover, these pre-existing diatheses may exert an influence on subjective stress even in the absence of clear objectively occurring stressors, with ambiguous or non-threatening situations being more likely to be interpreted in a negative manner (Beevers, 2005, Mathews and MacLeod, 2005).

The importance of cleanly observing the distinction between life stress and diatheses in testing etiological models of negative mental health outcomes becomes clear as research on life stress in several fields advances from predominantly stress exposure models (i.e., the notion that life stress temporally precedes and elevates risk for mental illness) to more nuanced diathesis-stress theories (i.e., the concept of mental illness as a product of pre-existing vulnerabilities and external stressors) or mediational models of psychopathology (Grant et al., 2003). With individual diatheses, in some measure, already incorporated in subjective stress ratings, evaluations of diathesis-stress models of psychopathology may be at greater risk for false negatives (i.e., Type II error); if the life stress variable is already a compound of objectively occurring stressors and the diathesis of interest, it stands to reason that an interaction between this variable and the diathesis is unlikely to account for a significantly greater amount of variance in the outcome. With assessments of mediators of the relation between life stress and mental illness, on the other hand, the concern instead is of an inflated association or even spurious effect (i.e., Type I error). Inasmuch as the life stress variable is confounded with the mediator of interest, the strength of the observed association between the two is likely to be exaggerated. Furthermore, the direct effect of the life stress variable on the outcome is likely to be spuriously reduced after accounting for this confounded mediator.

That life stress likely functions as a proximal predictor of NSSI is consistent with several theoretical conceptualizations of this behavior. Specifically, according to a four-function model of NSSI (Bentley et al., 2014, Nock and Prinstein, 2004, Nock and Prinstein, 2005), this behavior is reinforced by several distinct processes. These include two intrapersonal emotion regulation processes (negative reinforcement with the release of tension or decrease in negative affect following engagement in NSSI, and positive reinforcement, such as is involved in the need to feel pain or to act on feelings of guilt through self-punishment). Paralleling these two intrapersonal processes, two interpersonal functions underlying NSSI have also been identified (positive reinforcement, with NSSI serving as means of communicating the need for help and support, and negative reinforcement, such as the cessation of negative interpersonal interactions following NSSI). Such interpersonal functions may be especially pertinent in the case of individuals with impaired interpersonal problem-solving abilities and poor general communication skills (Hilt et al., 2008, Nock and Mendes, 2008). A common element across all four functions is the implied precipitating presence of a form of distress, such as that experienced when confronted with an acute stressor, the primary difference across the four functions being the reason for engaging in NSSI to cope with this distress.

Prominent across several different conceptualizations of the pathogenesis of NSSI is the view that those who engage in this behavior suffer from a compromised ability to tolerate distress and to regulate their emotions, such as when they encounter a stressful life event (Klonsky et al., 2003, Nock and Mendes, 2008). This view complements the four-function model of NSSI, the focus, however, being on the causal factors precipitating this behavior, rather than its contingent response. Support for this position comes from several studies documenting greater self-reported feelings of emotional distress in those who engage in NSSI when they experience stress (Najmi et al., 2007, Nock et al., 2008).

Although similarly not directly assessing life stress, several psychobiological studies of emotion regulation, distress tolerance, and laboratory stress induction tasks in relation to NSSI report findings also suggestive of the possibility that life stress may indeed have a central role in the etiology of this clinical phenomenon. In particular, one study found NSSI to be associated with heightened physiological reactivity (as indexed by skin conductance) in response to an experimentally induced stressor, as well as lower ability to tolerate the stressor (Nock & Mendes, 2008). In a more recent study, HPA axis dysregulation following an experimentally induced social stressor was found to be associated with NSSI (Kaess et al., 2012). Also indicative of the potential influence of life stress on the pathogenesis of NSSI, experimentally elicited recollection of recent negative interpersonal interactions appears to be associated with reduced distress tolerance among women who engage in NSSI (Gratz et al., 2011). In contrast, this diminished distress tolerance was not observed when induced recollection of interpersonal stressors was omitted.

Collectively, such findings have informed recent theoretical understandings of NSSI, with life stress more explicitly integrated into conceptual models of this behavior (e.g., Nock, 2009b, Nock, 2010). In particular, individuals at risk for NSSI may possess certain intrapersonal risk factors (e.g., a predisposition to experience diminished distress tolerance in response to stressful circumstances) and interpersonal vulnerabilities (i.e., poor interpersonal problem-solving and communication skills), which, when combined with life stress, particularly within interpersonal domains, may trigger dysregulated emotions. This emotion dysregulation, in turn, is resolved by engaging in NSSI as a means to alleviate feelings of distress, as a form of self-punishment, or as a method of interpersonal communication (Nock, 2009b, Nock, 2010).

Section snippets

Search strategy and eligibility criteria

A systematic search of the literature was conducted in PsycINFO and MEDLINE to identify studies of potential relevance to the current review. The following search string was applied: (self-injur* OR mutilat* OR self-cut* OR self-harm*) AND (life stress* OR stressor* OR event OR events). The search results were limited to: (i) English-language publications and (ii) journal publications. This search strategy yielded a total of 1379 articles, of which 1080 were unique reports. Each unique search

Results

Of the final set of 21 studies, 13 were included in the meta-analytic review, yielding 14 unique effects.3 The remaining studies were excluded from meta-analysis, but retained for qualitative review, because: (i) they featured samples included in other studies in the meta-analysis (n = 4); (ii) examined individuals with NSSI relative to a presumably more severe group (i.e., suicide attempters; n = 1); (iii) assessed life stress in an

Discussion

The current review aimed to present a systematic quantitative and qualitative analysis of the association between life stress and NSSI. The results were largely consistent in providing support for a stress exposure model of NSSI. In the meta-analysis, the pooled odds of engaging in NSSI were approximately 80% greater after experiencing life stress than when life stress was absent, a relatively modest effect size. After adjusting for publication bias, the weighted odds of engaging in NSSI were

Acknowledgements

Preparation of this manuscript was supported in part by the National Institute of Mental Health of the National Institutes of Health under Award Number R01MH101138 to the first author. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agency.

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    Articles marked with an asterisk were included in the meta-analysis.

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