Psychosocial Stress and Predicting the Early Onset of Asthma in Children
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Mary Klinnert, Ph. D.
Assistant Faculty Member, Department of Pediatrics,
National Jewish Medical and Research Center
Assistant Professor, University of Colorado Denver
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Introduction
A small but growing body of evidence points to a relationship between psychosocial stress and the early onset of asthma in children who have a genetic predisposition to the disease. Specifically, clinical judgment of "early parenting difficulties" has been found to be a significant predictor for the development of asthma among genetically at-risk children.
The W.T. Grant Foundation Asthma Risk Study was designed to prospectively examine children who were considered to be at a genetically increased risk of developing asthma. Since the longitudinal study began in 1985, researchers have monitored both physiological and psychological factors among 150 families with the intent of identifying risk factors for illness expression.
To date, the W.T. Grant study is the only study that has gathered longitudinal data from before the child's birth on the influence of psychological and psychosocial factors in the early onset of asthma. Data currently under review for publication indicate that psychosocial predictors measured early in life are associated not only with early asthma onset, but with the persistence of asthma to age 8 in the study cohort. The relationships between first year variables and school-age asthma support the belief that asthma begins in the first year of life.
Follow-up is continuing on this cohort of children, so it will be possible to determine whether these psychosocial influences from the beginning of life continue to relate to the occurrence of asthma in this study cohort when the subjects are 13 years old.
Environmental Risk Factors
Medical professionals consider asthma a familial illness. Family studies have demonstrated a significantly increased risk for the development of asthma in individuals who have affected relatives. However, genetic vulnerability does not guarantee that an individual will develop asthma. It is now accepted that the expression of asthma involves a genetic predisposition and exposure to environmental factors. Researchers have extensively investigated a number of environmental exposures in terms of their role in the onset of asthma.
- Respiratory viral infections - Clinical studies have demonstrated that the onset of asthma is often preceded by respiratory infections. The most commonly studied viral infection is respiratory syncytial virus (RSV), which in infants is often accompanied by wheezing symptoms.
- Specific antigens -Antigens from foods (e.g., milk, eggs, peanuts), dust mites, molds, animal dander, and cockroaches may stimulate a classic antibody response involving immunoglobulin E antibodies that could result in a persistent increase in the reactivity of this system.
- Nonantigenic irritants - Although smoke is the predominant substance in this category, a wide range of air pollutants may directly affect bronchial receptor systems or act through potentiating allergic mechanisms and result in greater reactivity to the antigens.
- Emotional stressors - Stress may lead to increased bronchial sensitivity or inhibit the immune response.
There have been supportive data for the role of each of the first three categories of exposures, although the significance and the mechanisms of each of them continue to receive extensive research attention. In contrast, the last of the four, emotional stressors, has received minimal consideration up to now. The W.T. Grant study has spent the last 14 years examining the associations among parental behavior, emotional stressors and later illness expression in genetically at-risk children. The data currently under review provide support for the contribution of psychosocial factors to asthma onset and persistence into childhood.
Parenting Issues
The original phase of the Grant study examined perinatal variables and the subsequent health status of the children in the sample cohort. To determine the primary caregiver's (typically the mother's) ability to cope with stress and modulate the effect of stress upon the children in the study, scales were developed and conducted in in-home interviews with the families three weeks after the baby was born.
To determine a rating of parenting skills, researchers examined the following six characteristics:
- Parents' attitudes towards the new infant
- Parents' sensitivity to their infant's needs
- Parents' effectiveness responding to the infant
- The nature of the parents' strategy for sharing parenting responsibilities
- Evidence of disturbed emotional adjustment that would affect infant care (e.g., postpartum depression)
- Adequacy of the plan of the parents to continue with employment while providing adequate child care
Besides rating parenting skills during the in-home interviews conducted 3 weeks after the child was born, ratings were made of mothers' coping with family demands, her ability to modulate stress for the infant, and her satisfaction with support provided by her partner. Additionally, researchers rated the temperament of the child at three weeks of age. The judgment was based on the maternal report of the child's rhythmicity and ability to be soothed during the first three weeks of life and the direct observation of the infant. Researchers also used standardized measures (the Minnesota Multiphasic Personality Inventory [MMPI] and the Dyadic Adjustment Scale) during the final trimester of the pregnancy with the index infant to measure aspects of the personality and adjustment of the parents that should be associated with parenting.
Asthma Onset
For the purpose of characterizing respiratory illness with bronchoconstriction, researchers defined three classes:
- Asthma - based on conservative diagnostic criteria that included recurrent wheezing episodes documented by the child's pediatrician (including at least one precipitated by an environmental trigger other than respiratory infection)
- Infectious Wheezing - defined as multiple wheezing episodes, each associated with a respiratory infection
- Single Wheezing Episode - classified as a single wheezing episode identified by the child's pediatrician that could have occurred with or without a respiratory infection.
Using information from the children's medical records, the children were classified into one of the above categories at age 3. Fourteen of the 150 were classified as having asthma (as defined above) and 19 were considered to have infectious wheezing. Twenty-four experienced a single wheezing episode, and the remainder demonstrated no wheezing at all.
Parenting difficulties and asthma onset
The clinical judgment of "early parenting difficulties" emerged as a predictor of asthma at age 3. Based on concerns about the parents' ability to deal with the young infant, elicited during the in-home interview, 52 of the infants had parents judged to be having parental problems. Of those infants, 9 (17.3%) subsequently developed asthma, compared with five (5.1%) of the infants whose parents were perceived as parenting their infant well.
Overall Difficulty
The parenting difficulties that were related to asthma onset were highly associated with the other interview ratings and provide insight into the range of problems captured by ratings of parenting difficulties. Mothers who were rated as having parenting difficulties were significantly more likely to be coded as coping poorly than were those rated as having adequate parenting. Similarly, difficulties in modulating the child's affect were highly significantly associated with ratings of parenting risk. Postpartum depression was rare in this sample, but when it did occur, depressed mothers were always coded as having parenting difficulties. Both the interview ratings and the Dyadic Adjustment Scale indicated that problematic marital satisfaction was highly associated with parenting risk. Mothers who were having parenting difficulties were more likely to have elevated scores on several scales from the MMPI, including depression and the tendency to disregard societal rules. Finally, a significant association was noted between parenting difficulties and a difficult temperament in the child, although the association between temperament and illness expression itself was not significant.
Caveats
It should be pointed out that these data cannot be considered representative of the general population. The study group was predominantly white, middle-to upper-middle-class. Also, capturing data at a single point (three weeks after the baby was born) does not capture data of later developments.
A variety of hypotheses could explain the associations between early parenting difficulties and early asthma onset. For example, highly adaptive parents may have resolved early viral infections without changing airway reactivity of the child, but bronchoconstriction may have been aggravated by emotional stress among children in a caregiving environment with parenting difficulties.
Parenting Skills and Stress Regulation
Conceptually, quality parenting modulates or buffers infants from external stress. If this were true, the infants in the W. T. Grant study whose parents demonstrated superior parenting skills would be protected from illness despite high or low levels of stress.
Researchers divided the sample into four groups based on stress levels reported using the Family Inventory of Life Events (FILE), a family-oriented inventory of life events designed to assess the impact of stressors in multiple family members and parenting risk ratings. The categories were:
- High stress/adequate parenting
- Low stress/adequate parenting
- High stress/problematic parenting
- Low stress/problematic parenting
Differential percentage of children with asthma at 3 years of age with different maternal stress and parenting problems (from Early Asthma Onset: The Interaction Between Family Stressors and Adaptive Parenting).
As illustrated in Figure 1, only 5.3% of children in families with low stress and adequate parenting developed asthma by age 3, compared with 25% of children in families categorized as having high stress and problematic parenting. Also, 4.4% of children in families with high stress and adequate parenting and 10.7% of children in families with low stress and problematic parenting expressed asthma.
These results indicate that stress is irrelevant when parenting risk is low, but when parenting risk is high, stress is more highly associated with asthma development. The findings suggest that, for families with problematic parenting, a high frequency of life stressors may overtax their coping capacity and place their children at increased risk.
Possible Predictors
The relationships between risk factors and asthma onset have still not been clearly defined. Few studies have included an adequate assessment of psychosocial variables among the predictive factors that have been examined. But the inclusion of psychosocial assessments adds an important dimension to efforts to define the relationships between risk factors and asthma onset.
The W. T. Grant study identified risk factors from previous studies and measured them prospectively in this cohort. The operational definitions utilized in the study for these factors are outlined in Table 1, Definition of Risk Factors.
Only four of the risk factors - frequent illness, 6-month IgE, parenting difficulties and eczema - demonstrated statistically significant associations with the early onset of asthma, as illustrated in Table 2, Risk Factors for Asthma Development by Age 3 Years, Ordered by Significance Level Using Contingency Table Analysis.
The occurrence of frequent infectious illness during the first year of life was the strongest predictive risk factor for the onset of asthma by age 3. It does not, however, elucidate the mechanism through which frequent infectious illnesses lead to asthma. Hypotheses include the promotion of IgE sensitization and the possibility that an underlying immunological vulnerability may be associated with both viral illness and reactive airway disease.
Elevated serum IgE measured at 6 months was a second independent and significant predictor for early asthma onset. Although studies initially had difficulty documenting a relationship between IgE levels at birth and the subsequent development of asthma, there is now evidence from other studies that IgE levels within the first year of life are associated with early asthma onset. Nevertheless, while IgE was a significant predictor, only 24% of the children who went on to develop asthma by age 3 years had an early elevation of total serum IgE at 6 months.
An association between early parenting difficulties and the onset of asthma has not been previously demonstrated. The association was particularly striking since it was independent of both frequent infectious illness and elevated total serum IgE. There are a number of possibilities that might account for the relationship between early parenting and asthma onset. The parenting ratings of problems at 3 weeks of age are likely related to parenting behavior over the following years, and may thus be a marker of parents' illness management. Parents who are able to respond promptly and effectively to early illness may play a role in delaying or preventing early asthma onset. Alternatively, the quality of early caregiving may affect the developing immune system through mechanisms that are as yet unknown. One study from another laboratory has demonstrated effects of the early socioemotional environment on the immune system, suggesting that such effects may occur.
Eczema was more prevalent among children who developed asthma by age 3. But, the occurrence of eczema did not add predictive variance after the first three variables. Perhaps elevated 6-month IgE levels contributed to the model most of the variance attributable to early allergic status. However, the presence of eczema in the first year was not significantly associated with elevated IgE at 6 months. Nevertheless, the association between eczema and early-onset asthma provides further support that the classification of asthma utilized in the W. T. Grant study defines early instances of atopic asthma.
Two of the variables assessed were marginally associated with asthma onset by age 3. More males than females had asthma by age 3, and the failure of this relationship to reach significance is probably due to lack of statistical power given the sample size. Interestingly, length of breastfeeding was also marginally related to asthma onset. This is more difficult to interpret, given that other studies have been equivocal in their support for a relationship between breastfeeding and asthma onset. Other studies that defined a protective effect of breastfeeding may have defined asthma differently. Furthermore, maternal diet and the nature of the infants' early diets were not analyzed and may have influenced the effect of breastfeeding.
The lack of a relationship between socioeconomic status and asthma onset at age 3 was probably related to the relatively small sample size as well as to the homogeneity of the group. Although the sample included families across a socioeconomic range, there were relatively few at the lower end of the scale. Similarly, the lack of relationship in this study between passive smoke exposure and asthma onset by age 3 was probably due to the very small number of families reporting significant smoke exposure.
The relationship between any risk factor and the onset of asthma continues to be the focus of investigations both nationally and throughout the world. But, the documentation does provide potential guidance for asthmatic parents who seek advice regarding how to minimize their child's risk of developing asthma. Given these findings, asthma prevention efforts could be designed to reduce exposure to multiple risk factors.
References
Klinnert, MD, Mrazek, P., and Mrazek, D.A. (1994), Early asthma onset: The interaction between family stressors and adaptive parenting. Psychiatry , 57, 51-61.
Mrazek, D.A., Klinnert, MD, Mrazek, P., IklÇ, D., Brower, A., McCormick, D., Macey, T., Rubin, B., Larsen, G., and Jones, J. (1999), Prediction of early onset asthma in genetically at risk children. Pediatric Pulmonology , 27, 85-94.
