Maternal intimate partner violence predicts increased asthma incidence in children: Buffering effects of supportive caregiving

Abstract

OBJECTIVES

To examine the relationship between maternal intimate partner violence (IPV) and asthma onset in children and the role of supportive caregiving factors in modifying this relationship.

DESIGN

Prospective birth cohort.

SETTING

In-person interview at enrollment as well as in-home interviews during study follow-up.

PARTICIPANTS

Children (N=3116) enrolled in the Fragile Families and Child Wellbeing Study.

MAIN EXPOSURES

Maternal-report of IPV assessed after the child’s birth and at 12 and 36 months. In addition mothers indicated how many days a week they participated in activities with the child and the amount and type of educational/recreational toys available for the child.

MAIN OUTCOME

Maternal-report of physician-diagnosed asthma by age 36 months.

RESULTS

Asthma was diagnosed in 19% of children. In adjusted analysis, children of mothers experiencing IPV chronically, compared to those not exposed, had a 2-fold increased risk of developing asthma. In stratified analysis, children of mothers experiencing IPV and low levels of mother-child activities (RR 2.7, 95% CI 1.6, 4.7) had a significant increased risk for asthma. Those exposed to IPV and high levels of mother-child activities had a lower risk for asthma (RR 1.6, 95% CI 0.9, 3.2). A similar buffering effect was noted among children with high numbers of educational/recreational toys.

CONCLUSIONS

IPV is associated with increased early childhood asthma risk. Maternal ability to maintain positive caregiving processes in this context may buffer the effects of violence on child asthma risk. The best way to promote positive health in toddlers may be to help their mothers.

Introduction

Evidence linking psychological stress to asthma continues to grow with our increased understanding of the natural history of asthma and the neurobiology underlying stress vulnerability ^1–3. Stress exposure during infancy and early childhood may exert particularly robust effects on the physiological systems that respond to stress ^4–6. Evidence from animal and human studies strongly suggests that early life adversity shapes stress neurobiology ⁷, resulting in disturbed regulation of endocrine and autonomic processes [e.g., hypothalamic-pituitary-adrenal (HPA) axis, sympathetic-adrenal-medullary (SAM) system]. These disturbed patterns of stress regulation are hypothesized to subsequently modulate immune function, increasing susceptibility to asthma and related diseases ⁸.

Developmental psychologists purport that the ability to regulate one’s responses to stress (“self-regulation”) emerges in the context of the caregiver-child relationship, particularly in the first three years of life. Self-regulation involves the ability to modify the intensity and duration of physiological arousal, attention and affective states in order to protect oneself from becoming overwhelmed by stimulation and modulate one’s emotional expressions and social behaviors ^{9, 10} and is an important predictor of resilience among children ^11–13. That is, in the face of stress, children with good self-regulation skills have better adaptive behavior and coping strategies ¹². In the infancy and toddler periods, sensitive and emotionally engaged caregiving has been found to buffer the reactivity of the child’s stress regulation systems and promote state and arousal regulation at the physiological, affective, and behavioral levels, with self-regulation emerging as a major developmental milestone of the preschool period ^{14, 15}. It has been proposed that insensitive maternal-child interactions in early life may result in disturbed stress reactivity and impaired self-regulation abilities and consequently, disrupted neuroimmune development, setting the stage for asthma ⁷. Notably, increased levels of negative affect and emotion dysregulation have been documented among children with severe asthma ¹⁶. Also, among children with asthma, difficulties with emotion regulation have been found to increase asthma severity ⁶, supporting a link between regulation and asthma.

Considering the caregiver’s critical role in shaping the child’s stress regulation systems in early development, factors that increase maternal stress and influence parenting behaviors may be particularly relevant in the etiology of asthma ^{17, 18}. Maternal exposure to intimate partner violence (IPV) has been identified as such a stressor. Cross-sectional evidence suggests that maternal IPV is associated with decreased lung function ¹⁹, increased child asthma risk in early development ²⁰ as well as children’s behavioral and physiological stress reactivity and emotional and behavioral development ^21–23. However, it is important to note that, while mothers experiencing IPV show increased levels of stress, they do not always show deficient parenting. Van Horn and Lieberman (2002) suggest that women experiencing IPV are remarkably similar to comparison women in their beliefs about parenting, self-reported parenting behaviors, and observed interactions with their children ²⁴. Other evidence shows that while some mothers in violent relationships were struggling with parenting, other mothers seemed to compensate for the violence by becoming more effective parents ²⁵. Therefore, the effects of maternal IPV on child health outcomes may be attenuated if mothers are able to maintain supportive caregiving in this context.

The goal of the current study was to prospectively examine associations between maternal IPV and child asthma risk and to consider the potentially buffering effects of the maintenance of supportive caregiving on this relationship. The supportive caregiving factors included in the current analyses—positive maternal-child activities and cognitive stimulation—have been associated with the development of optimal child self-regulation abilities ^26–29.

Methods

Study Population

Analyses were conducted using public-use data available from the Fragile Families and Child Wellbeing Study, a prospective birth cohort study that follows a nationally representative sample of children from 20 large cities in the United States (US). Non-marital births were over-sampled relative to marital births in a ratio of 3 to 1. The study is a joint effort by Princeton University’s Center for Research on Child Wellbeing (CRCW) and Center for Health and Wellbeing, Columbia University’s Social Indicators Survey Center, and The National Center for Children and Families (NCCF) (http://www.fragilefamilies.princeton.edu). Details on the study design can be found in Reichman et al 2001 ³⁰. In brief, 4789 women were recruited from 75 hospitals during the birth of the child in 20 US cities with populations over 200,000. Random samples of both married and unmarried births were selected until preset quotas were reached based on the percentage of non-marital births in the city that occurred at that hospital in 1996 or 1997. Families were excluded if any of the following criteria were met: mother planned to place the child for adoption; father of the baby was not living at the time of the birth; mother did not speak either English or Spanish well enough to complete the interview; mother or baby was too ill for the mother to complete the interview; baby died before the interview could take place. Among eligible mothers, 82% of those married and 87% of those unmarried agreed to participate. Mothers completed a baseline interview at delivery and participated in follow-up interviews when the children were approximately 12 and 36 months of age. At the time of the 36-month in-home assessment, 3288 families remained in the study ³⁰. No significant differences were found between those who did and did not complete the 36 month follow-up assessment on baseline demographics or IPV exposure. In addition, 172 children were missing data on other covariates, leaving 3116 children for the current analyses.

Intimate Partner Violence Assessment

Maternal IPV was assessed at baseline and at the 12- and 36-month assessments, with study questions, previously validated ^31,32, varying slightly between baseline and follow-up assessments. At baseline, mothers were asked to think about their relationship with the baby’s father and asked how often does “he hit or slap you when he is angry?” Mothers who responded, ‘often’ or ‘sometimes’ as opposed to ‘never’ were categorized as experiencing baseline IPV. At 12 and 36 months, mothers were asked to think about their relationship with the baby’s father or current partner and were then asked: “How often does he slap or kick you?”, “How often does he hit you with a fist or object that could hurt you?”, and “Were you ever cut or bruised or seriously hurt in a fight with the baby’s father or current partner?”. Mothers who responded ‘often’ or ‘sometimes’ as opposed to ‘never’ to either of the first two questions or who responded ‘yes’ to the third question were categorized as experiencing IPV for the relevant follow-up period. Physical IPV was characterized as: (a) never experiencing IPV (b) occurring prior to 12 months only (endorsed at baseline and/or 12-month follow-up), (c) occurring between 12 and 36 months only (endorsed at 36 months only), or (d) occurring both prior to 12 months and also between 12 and 36 months (chronic exposure).

Asthma Outcome

During the 36 month follow-up interview, mothers were asked whether a physician had diagnosed the child with asthma, a standard approach with demonstrated reliability and validity. Parent-reported physician-diagnosed asthma is associated with more objective outcomes (e.g., airway hyperresponsiveness) and more severe disease ³³. Moreover, this definition is used by the National Center for Health Statistics in surveys of the US population to facilitate generalizability³⁴.

Supportive caregiving

Based on prior work on caregiving characteristics important in the development of self-regulatory processes ^{27–29, 35, 36}, factors reflective of supportive caregiving were categorized across two domains: engagement in mother-child activities and availability of educational/recreational toys as a measure of cognitive stimulation. Both factors were assessed at the 36-month assessment.

Mothers reported how many days a week they gave the child physical affection (e.g., told the child she loved him/her, gave the child hugs or physical affection), spent time with the child in various activities (e.g., read or told stories, played with toys or imaginary games, and sang songs) and assisted the child with eating and bedtime. Exploratory factor analysis using orthogonal rotation was employed to uncover the number of latent constructs underlying this set of ten items. A cutoff of 0.40 was used for factor loading with an eigenvalue greater than one, which allows the extracted factor to explain a reasonable proportion of the total variance. Principal components analysis of the 10 items revealed three factors which explained 52% of the total variance: one factor included the two items on physical affection, a second factor included the six items on mother-child activities, and a third factor included the two items on eating and bedtime. Closer examination revealed that 98% of the mothers reported expressing physical affection toward their child every day and 97% reported telling the child she loved him/her every day. Because of the limited variability of these two items, a scale of mother-child activities was created summing the six items that loaded onto the second factor, corresponding to activities such as reading, singing songs, telling stories, playing with toys or playing imaginary games. Scale scores ranged from 0 to 42, with higher scores indicating a higher number of different activities and a higher frequency of activities. Scale reliability was found to be adequate, Cronbach’s α = .74.

Mothers quantified the number of educational materials and recreational toys available in the home, including books, toys that make music, toys that have pieces that fit together, push or pull toys, toys that let the child work his/her muscles, toys that can be put together in different ways, cuddly toys, and toys with wheels. Mothers were asked whether their children owned none, 1–2, 3–4, or 5 or more of each of these types of toys/books. Principal component factor analyses revealed two factors which explained 50% of the total variance: one factor for the six toy items and another factor with two items (books and cuddly toys). Because 90% of mothers reported their children owned five or more books, a scale consisting of educational/recreational toys was created by summing the six items on toys. Scale scores ranged from 0–18, with higher scores indicating a higher number of toys as well as a greater diversity of toys. Scale reliability was found to be adequate, Cronbach’s α = .75.

Covariates

The baseline and follow-up questionnaires ascertained information on sociodemographic factors, including maternal race/ethnicity, maternal education level, and child gender, as well as maternal smoking and birth weight of the child. Racial/ethnic minorities as well as those of lower socioeconomic status (SES) experience higher rates of family violence as well as higher rates of asthma ³⁷ than their white, higher SES counterparts ^38–40. Analyses were therefore adjusted for maternal race/ethnicity and maternal education level. We further adjusted for SES based on maternal report on whether they had faced any of the following economic hardships in the past year (yes/no): not having enough money to pay full electricity, gas or oil bill; having to borrow money from friends or family; moving in with other people because of financial problems; staying in a shelter, car or abandoned building; being evicted from their home; not having enough money to pay rent or mortgage; receiving free food or meals. Economic hardship in the past year was categorized as responding “yes” to one or more of the above questions. Women who experience IPV are also more likely to have lower birth weight babies ⁴¹, a risk factor that has also been linked with increased childhood asthma risk ^{42, 43}. Birth weight was categorized as less than 2.5 kg compared to 2.5 kg and above. Furthermore, because smoking (maternal and other sources) has been shown to be associated with more stressful violent environments ^44–46 and with asthma prevalence ⁴⁷, tobacco exposure was included as another potential confounder. Mothers reported whether they smoked during pregnancy at the baseline assessment. During follow-up assessments, mothers were asked to report on their current smoking status and whether anyone in the household smoked. Child tobacco smoke exposure was categorized as follows: (a) no exposure; (b) postnatal tobacco smoke exposure only; and (c) both in utero and postnatal tobacco smoke exposure. There were few children with in utero tobacco exposure but no postnatal exposure (3.5%, n=110); hence they were included in the in utero and postnatal tobacco smoke exposure category.

Statistical Analyses

Summary measures of continuous covariates are reported as mean and standard deviation (SD) unless otherwise noted. Logistic regression analyses were conducted to estimate the effect of maternal IPV on asthma diagnosed by age 36 months while adjusting for potential confounders (child’s gender, age, race/ethnicity, low birth weight, maternal education, economic hardship, and tobacco exposure). First, a model was run regressing maternal IPV, occurring during at least one time point (ever), on child’s asthma diagnosis. Next, a regression model was run accounting for chronicity of exposure to maternal IPV (exposure in both postnatal time periods). Lastly, two separate logistic regression models were run regressing maternal IPV on child’s asthma diagnosis, stratified by the supportive caregiving factors: mother-child activities (model 1) stratified by the median score of the scale and educational/recreational toys (model 2), stratified by the median score of the scale. All analyses were conducted in SAS version 9.0 (SAS Institute, Cary, NC).

Results

Among the 3116 children available for analyses, 52% are boys, 48% are Black, 26% are Hispanic, 19% had been diagnosed with asthma, and 16% lived in a household with maternal IPV at some time during follow-up (Table 1). The mean score on the mother-child activities scale was 31, SD 8.6, and the mean score in the educational/recreational toys scale was 12, SD 3.8. The mother-child activities scale and the educational/recreational toy scale were moderately correlated, r = 0.25, p < 0.0001. Neither scale was significantly correlated with SES p > 0.05.

Table 1.

Demographics, Fragile Families and Child Wellbeing (N=3116)

Demographics	N	%	Mean	SD
Child’s age (Months)			38.5	3.2
Child’s Gender
Male	1626	52.2
Female	1490	47.8
Race/Ethnicity
White	685	22.0
Black	1506	48.3
Hispanic-Mexican	471	15.1
Hispanic-Other	335	10.8
Other race/ethnicity	119	3.8
Mother’s Highest Education Level Attained
Some College	1298	41.6
High School Graduate/Tech School	956	30.7
Less than High School/No Graduation	863	27.7
Low Birth Weight (Less than 2.5 kg)	303	9.7
Environmental Factors
Tobacco Exposure
Non-smoker	1842	59.1
In utero and Post-natal Tobacco Smoke Exposure	600	19.3
Post-natal Second Hand Smoke only	674	21.6
Supportive Caregiving
Mom and Child Activities 1 (Range 0–42)			31.4	8.6
Educational/Recreational Toys (Range 0–18)			11.6	3.8
Other stressors
Economic Hardship (one event or more)	1404	45.1
Violence Exposure
Intimate Partner Violence (IPV)2
IPV prior to 12 months	238	7.6
IPV between 12 and 36 months	150	4.8
IPV chronic	116	3.7
Physical IPV Ever	504	16.2
Asthma
Asthma diagnosis	586	18.8

¹Days a week you read or tell stories with child, play with toys or imaginary games and sings songs

²Intimate Partner Violence defined as physical abuse as reported by the mother

In adjusted analysis, children of mothers experiencing IPV at any time point, compared to those not exposed, were at increased risk of developing asthma [relative risk (RR) = 1.3, 95% confidence interval (CI) 1.0, 1.7]. Children of mothers experiencing IPV in only one time period, that is, prior to 12 months or at 36 months only, did not have a significant increased risk for asthma compared to children never exposed (Table 2). Those exposed to IPV during both time points (chronic exposure) had a 2-fold risk (RR: 2.1, 95%CI: 1.4, 3.2) of having an asthma diagnosis.

Table 2.

Risk of child asthma by maternal intimate partner violence (IPV) at different developmental time points

	Asthma
	RR (95%CI)
No IPV	(Ref.)
IPV (prior to 12 months)	1.1 (0.8–1.6)
IPV (between 12 and 36 months)	1.1 (0.7–1.7)
IPV (chronic)	2.1 (1.4–3.2)

Adjusted for child’s age, gender, age, race/ethnicity, maternal education, economic hardship, tobacco exposure, and low birth weight

In stratified analyses, children of mothers experiencing IPV chronically and who had a lower level of mother-child interactions were at increased risk of developing asthma (RR: 2.7 95%CI: 1.6, 4.7) compared to those not exposed to IPV with low mother-child interactions (Figure 1). No significant associations were noted among children of mothers experiencing IPV chronically and high mother-child interactions (RR: 1.6 95%CI: 0.9, 3.2) compared to those not exposed with high mother-child interactions. Similarly children of mothers experiencing IPV chronically and with low levels of educational/recreational toys were at increased risk of developing asthma (RR: 2.5 95%CI: 1.5, 4.1) compared to those not exposed with low levels of educational/recreational toys (Figure 2). Children of mothers experiencing IPV chronically with higher levels of educational/recreational toys did not have an increased risk of developing asthma (RR: 1.6 95%CI: 0.8, 3.4) compared to those not exposed with high levels of educational/recreational toys.

Figure 1. Risk of child asthma by maternal intimate partner violence stratified by mother-child activities.

Models were adjusted for child’s age, gender, race/ethnicity, maternal education, economic hardship, tobacco exposure, and low birth weight

Figure 2. Risk of child asthma by maternal intimate partner violence stratified by availability of educational/recreational toys.

Models adjusted for child’s age, gender, race/ethnicity, maternal education, economic hardship, tobacco exposure, and low birth weight

Discussion

These prospective data demonstrate that maternal IPV is associated with increased early childhood asthma risk. Cumulative or chronic exposure to violence was most clearly associated with asthma risk, consistent with the notion that stress beginning in infancy may sensitize children to later stress and more adverse consequences. This is consistent with the findings of Essex and colleagues (2002), who examined associations among maternal stress and preschoolers’ physiological stress response and later mental health ⁴⁸. Analyses showed that children exposed to stress only in infancy or only in the preschool period had cortisol levels similar to those never exposed to stress, whereas children exposed to maternal stress in infancy and preschool had elevated cortisol levels. These findings are also in line with other studies that have shown that chronic caregiver stress in the postpartum and early childhood period have been associated with persistent wheeze in early childhood ⁴ as well as factors that may initiate or potentiate inflammation in the lung (e.g. IgE expression, enhanced nonspecific and allergen-specific lymphocyte proliferation, differential cytokine expression) ^{5, 49}. Both persistent wheeze and atopy have been linked to reduced lung function in childhood ⁵⁰. This cumulative stress model is particularly relevant given that maternal IPV may become a more direct stressor for toddlers who are witnessing violence against their mothers ⁵¹.

Our analyses further show that, while maternal IPV is associated with increased childhood asthma risk, factors contributing to a supportive caregiving environment appear to buffer the maternal IPV-asthma association. While no other studies, to our knowledge, have explored the buffering effects of the caregiving environment in the stress-asthma association, animal studies have shown that environmental enrichment can reverse the effects of early stress experiences on stress reactivity ⁵². Laviola et al and Morley-Fletcher et al have shown that environmental enrichment eliminates the outcomes of prenatal stress on corticosterone response and reactivity to an immune-suppressive agent ^{53, 54}. Similarly Francis et al has shown that environmental enrichment can reverse the effects of early stress on HPA activation and behavioral response to stress ⁵⁵. In humans, parental social support has been shown to be inversely associated with asthma prevalence among children ⁵⁶ furthermore maternal sensitivity has been shown to modify the effects of prenatal stress experiences on infant stress reactivity ⁵⁷.

The stress-health paradigm provides a useful framework to link maternal IPV to child health effects. Numerous studies suggest that maternal stress experienced in utero influences programming of key physiological systems that contribute to childhood disease ⁵⁸ and that non-optimal early childhood environments and caregiving experiences also influence these processes^59–62. Specifically, emerging data implicate the disruptive impact of stress on the HPA, autonomic, neuroendocrine, and immune systems ^{1, 3, 7, 58, 63}. Disruptions of these stress regulatory systems may, in turn, be linked to immune dysregulation, increasing vulnerability to the development of diseases such as asthma.

In humans, both the HPA system and the autonomic nervous system show developmental changes in infancy, with the HPA axis becoming organized between 2 and 6 months of age, and the autonomic nervous system demonstrating relative stability by 6 to 12 months of age ⁶⁴. The HPA axis in particular has been shown to be highly responsive to child-caregiver interactions, with sensitive caregiving programming the HPA axis to become an effective physiological regulator of stress and insensitive caregiving promoting hyper- or hypo-reactive HPA systems ¹⁷. Several animal models as well as human studies also support the connection between caregiver experiences in early postnatal life and alterations of autonomic nervous system balance ^64–66. Furthermore, children who have a history of sensitive caregiving are more likely to demonstrate optimal affective and behavioral strategies for coping with stress ^{67, 68}. Therefore, children with histories of supportive, sensitive caregiving in early development may be better able to self-regulate their physiological, affective, and behavioral responses to environmental stressors and, consequently, less likely to manifest disturbed HPA and autonomic reactivity that put them at risk for stress-related illnesses such as asthma.

While these data allow us to explore prospective relationships between maternal IPV and childhood asthma, there are limitations worth mentioning. As is typical with longitudinal studies, there was a reduction in the sample available from the original cohort over time. However there were no differences based on race/ethnicity, maternal education, smoking status, low birthweight, or maternal IPV at baseline between those who completed the 36-month assessment and those who did not. While we were able to adjust for a number of factors associated with asthma and violence exposure, the associations found in this study may be attributable to unmeasured or residual confounding. For example, we were unable to adjust for traffic exposures or other environmental exposures which have been shown to affect asthma and to be more common in lower SES, higher social risk households ⁶⁹. It is possible that mothers may have underreported IPV or over-reported positive caregiving factors to present more socially desirable responses. However, this potential misclassification of exposure is likely non-differential with respect to the outcome, and thus unlikely to account for the observed associations. A lack of a buffering effect of caregiving factors among children exposed to IPV before the 36 month follow-up could be due to the timing of the assessment of caregiving factors, which occurred at the 36-month assessment. Quality of parental caregiving has been shown to be relatively stable over time, with changes in caregiving quality predicted by changes in maternal life circumstances (e.g. changes in overall life support, increase in life stress, and change in partner status).⁶⁸ It is likely then that in a population where IPV is not stable over time, parental caregiving practices are also changing.

This study demonstrates a relationship between chronic maternal IPV and development of childhood asthma. Furthermore, our results suggest that supportive caregiving may buffer the effects of violence: Among children chronically exposed to IPV, a lower risk of asthma was found among children with higher levels of positive mother-child interactions and cognitive stimulation. While public health intervention should be aimed at eliminating maternal IPV, understanding factors that can buffer the effects of domestic violence in children may inform prevention strategies that can potentially benefit not only their psychological well being, but also their physical health. The best way to promote positive health in infants and toddlers may be to support their mothers and intervene around factors influencing parenting behaviors, including intimate partner violence.

Abbreviations

HPA

hypothalamic-pituitary-adrenal

IPV

Intimate Partner Violence