Intimate partner violence
(IPV), as defined by the Centers for Disease Control and Prevention (CDC), involves physical or sexual violence or threat of such violence between current or former spouses or intimate partners. Acts of psychological aggression and emotional maltreatment also comprise IPV, particularly when there has been a history of threats or physical or sexual aggression in a relationship.1
Women's lifetime IPV rates sampled from 10 nations range from 15% (Japan) to 71% (Ethiopia), with a rate of 25% in the United States.2,3
Compared with other examples of interpersonal victimization, such as a physical assault by a stranger, the assaultive and aggressive acts in situations of IPV can sometimes occur repeatedly over years. These acts may cause injury, fear, and perceived life threat, the elements of traumatic stress. Further, between occurrences of discrete aggressive incidents, a context of fear may persist. Thus, as a stressor, IPV can be both chronic and traumatic.4
In data from a nationally representative U.S. sample, for example, two thirds of women physically assaulted by an intimate partner reported an average of 6.9 assaultive acts over 4.5 years.3
In a survey of female enrollees of a U.S. health maintenance organization, nearly 50% reported ≥6 years of psychological aggression.5
Two population-based, cross-sectional studies reveal the significance of IPV for women's health. Lifetime IPV occurrence predicted elevated prevalence of aging-related chronic medical conditions, including conditions where the pathophysiology involves inflammation (e.g., heart disease, stroke, cancer, joint disease). These associations held after adjusting for demographic and behavioral risks6
and after establishing the temporal precedence of IPV by excluding women for whom disease onset preceded IPV.7
Compared to other significant life stressors (e.g., caregiving for a relative with dementia), there have been few efforts to identify biologic mediators connecting IPV and poorer health. One exception focused on stimulated in vitro
production of the cytokine interferon-γ (IFN-γ), an early mediator of the immunologic process that promotes inflammation.8
IFN-γ production was significantly greater in a group comprising women who reported either past or present partner violence, compared to women reporting no abuse. This association was fully mediated by current posttraumatic stress disorder (PTSD) symptoms that were largely comorbid with depression. The present study approaches this problem by focusing exclusively on women with past IPV and by considering the biologic measures C-reactive protein (CRP) and interleukin-6 (IL-6).
Although neither CRP nor IL-6 has been examined within the context of IPV, both could plausibly contribute to its association with multiple chronic conditions. CRP and IL-6 are biologically linked, but they have distinct functions. CRP is classified as an acute-phase protein; it assists in the recognition and elimination of pathogens and damaged cells9
and is widely used to index systemic inflammation. IL-6 is a cytokine, a protein that facilitates communication between cells. It stimulates CRP synthesis and is, therefore, generally considered proinflammatory, but it also has anti-inflammatory properties.10,11
Although there are exceptions,12
some prospective studies of apparently healthy persons reveal that elevated IL-6 and CRP circulating levels predict emergence of multiple aging-related chronic conditions and mortality.13–15
Circulating CRP and IL-6 levels are also stress reactive. For example, CRP and IL-6 elevations have been shown to accompany ongoing chronic stressors, such as fear of terrorism16
and caregiving for a relative with dementia,17
although again there are exceptions.18,19
The stress-reactive quality of IL-6 and CRP is consistent with data showing that key biologic stress mediators, glucocorticoids and catecholamines, influence cytokine production.20
Despite having some shared correlates and despite being biologically linked, IL-6 and CRP sometimes independently predict health risk,21
and other times they show divergent associations with both health outcomes22
Especially pertinent to the present study is evidence that chronic stress, even after it has remitted, is associated with accelerated age-related increases in circulating IL-6.17
Despite daunting obstacles, many women leave violent relationships. Paradoxically, violence sometimes continues or escalates after separation.3,23
This threat intensification, combined with the possibility of enduring biologic consequences of remitted chronic stress, underscores the relevance of research with women who have experienced past IPV.
Accordingly, the present study evaluated CRP and IL-6 levels in women with histories of divorce or separation. All women, midlife and postmenopausal, were at a biologic transition characterized by increased risk for aging-related chronic diseases. A prior report on this sample focused on relations among circulating inflammatory mediators from multiple biologic fluids.24
CRP levels were higher among women with histories of IPV (defined as one or more severe instances of physical assault or sexual coercion) compared to those without. The present article extends this prior report in three ways.
First, specific IPV types—physical assault, sexual coercion, stalking, and psychological aggression—are the focus here. The impetus for this is the multidimensional nature of IPV and evidence from preclinical research for stressor-specific biologic correlates.25
This exploratory aim is designed to move beyond a global, dichotomous measure of IPV and generate new information about IPV types potentially most relevant for biologic mediators of inflammation.
Second, in addition to CRP and IL-6 circulating levels, which are products of multiple cell types, this article reports on in vitro
IL-6 production by stimulated peripheral blood mononuclear cells (PBMCs), a model of the capacity of immune system cells to produce IL-6 when challenged. To our knowledge, this has not been evaluated in the context of remitted chronic stress, but ongoing interpersonal stressors persistent for 1–6 months show positive associations with stimulated IL-6 production from PBMCs or whole blood.18,26
Third, this article evaluates whether relations between past IPV and biologic measures are accounted for by current symptoms of depression and PTSD. Symptoms of both disorders have been associated with elevations in stimulated IL-6 production and IL-6 and CRP circulating levels in some studies.27–30
Despite this and despite the fact that such symptoms arise in the context of life stressors, very few studies of IL-6 and CRP have addressed stressors and symptoms simultaneously.28,31,32
In addition to its conceptual advantages, this approach has practical relevance because associations with symptoms could suggest potential avenues for intervention.