Effect of exposure to poverty, biological vulnerability, and early psychosocial vulnerability on the occurrence of asthma attacks among seven year olds in the Quebec birth cohort

Background

Asthma is one of the most common childhood diseases which disproportionately burdens poor children in developed countries. Early exposure to stressful situations such as material deprivation, biological vulnerability, and psychosocial hardship are hypothesized to increase the occurrence and severity of asthma. The availability of universal health care coverage is thought to attenuate the deleterious health effects of poverty and vulnerability although limited data exist to support this assertion. Therefore, this study examined the role of biological and psychosocial vulnerabilities, and poverty in explaining the occurrence of asthma attacks among children of the Quebec Longitudinal Study of Child Development.

Method:

We used data from the first eight waves of the Quebec Longitudinal Study of Child Development (QLSCD). The QLSCD is the only ongoing birth cohort study in Canada that has been followed without interruption since 1998. A representative sample of 2120 singleton infants was recruited at the age of 5 months and followed-up annually at home to assess their development and health in relation to their upbringing conditions at the household and community levels.

From mother reports, we established the occurrence of asthma attacks between the ages of six and seven years. Children having experienced one asthma attack or more were contrasted to those not having had any asthma attacks. Main exposure variables included: number of 12-month periods of living in poverty before four years old, living in poverty at age seven years; an index of biological vulnerability (male, second born or over, preterm); an index of psychosocial hardship in the first four years of life (single parenthood, maternal depression, unsafe neighborhood, difficult temperament). Poverty was operationalized as having a household income during the previous 12 months below the Canadian low-income cut-off (LICO) which accounts for household size and size of community of residence. Bivariate and stratified analyses were carried out to assess main effects of exposure variables and interactions between poverty and both psychosocial and biological vulnerability respectively. Analyses will be furthered by examining medical diagnosis of asthma since birth and by performing logistic regressions to control for potential confounding variables.

Results

A total of 1528 children made up the sample at age seven years for a participation rate of 72.1% at that age. Among them, 15% were living within poverty and 14% spent most of their first four years of life living in poverty (3 or 4 12-month periods out of 4). We estimated that, at age seven years, 4.6% of QLSCD children had experienced an asthma attack in the previous 12 months. Almost 11% of the poor children endured an asthma attack at least once in the previous 12 months compared to 4% among children of better-off households. The prevalence of at least one asthma attack was 31% when all indicators of biological vulnerability were present versus 4% when none was present; asthma attack prevalence was 10.1% in presence of all psychosocial hardship factors versus 2.5% without psychosocial hardship factors. In a logistic regression model, exposure to poverty at age 7 years (OR=2.47, 95%CI: 1.43, 4.25) acted additively to biological vulnerability (OR= 9.13, 95%CI: 2.13, 31.70) and psychosocial hardship (OR= 4.27, 95%CI: 1.23, 14.89) in increasing the likelihood of experiencing at least one asthma attack. Preliminary stratified analysis suggested that poverty interacted with biological vulnerability to increase the likelihood of asthma attacks between the age of six and seven years.

Conclusion: Poverty may act jointly with biological and psychosocial vulnerabilities in producing poor child health outcomes even in the context of universal health care coverage. These preliminary results suggest that adverse early childhood upbringing circumstances and poverty later on in childhood might have long term impacts on the child's risk of asthma attacks, independently or interacting with biologic risk. Strategies to address both poverty and vulnerability are required. Reduction of poverty should be a priority.

Acknowledgements: The study was funded by the Canadian Institutes of Health Research Grant #200309MOP-123079 and Grant #200609MOP-165867 and by the Institut de la Statistique du Québec, Direction Santé Québec who was responsible for the data collection and validation.

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