Childhood social position and associations between environmental exposures and health outcomes

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Abstract

Background

Growing evidence indicates that environmental exposures are more prevalent among socially disadvantaged groups. We investigated the distribution of environmental exposures and health outcomes in preschool children, and examined the role of social position on their associations.

Methods

We analysed data from a cross-sectional study on 968 preschool children from three districts in the Ruhr Area and one rural community in North Rhine-Westphalia in 2000. Parents filled in a questionnaire on socio-demographic characteristics, environmental exposures, respiratory infections and allergic diseases. Residential annual total suspended particulate matter (TSP) mass concentrations were derived from a small-scale interpolation model. Lung function, allergic sensitisation and immunologic function were assessed. We analysed the associations between environmental exposures and health outcomes in social subgroups with logistic regression.

Results

High TSP concentrations at the home address and unfavourable living conditions were more prevalent in the socially disadvantaged groups, while allergic and respiratory infectious diseases were reported more frequently in the privileged groups. The odds ratio for the association between TSP and history of allergic diseases was 1.17 (95% CI 0.95–1.45) in children without immigration background and 0.71 (95% CI 0.53–0.95) with immigration background. Heterogeneity for exposure–outcome associations was also seen between TSP and lung function as well as unfavourable living conditions and allergic diseases.

Conclusions

We found evidence for an influence of social position on environment–health associations. Possible explanations for heterogeneity include social group-specific over- and underreporting and effect measure modification, which need to be taken into account when designing and analysing environmental health studies.

Introduction

Social position is a determinant of health, with gradients for multiple health outcomes (Beckett et al., 1996; Mackenbach et al., 1997; Marmot, 2001; O’Neill et al., 2003). Low social position has also been found to be positively associated with numerous hazardous environmental exposures, including environmental risk factors concerning respiratory and allergic diseases like exposure to ambient and indoor air pollutants and allergens (Bolte et al., 2006; Bolte, 2006; Chaix et al., 2006; du Prel et al., 2005; Evans and Kantrowitz, 2002; Gunier et al., 2003; Lannerö et al., 2002).

Recent studies have focused on examining the associations between socioeconomic status (SES) and environmental health, hypothesising that groups of lower SES carry a disproportionate burden of environmentally related diseases (Bolte and Mielck, 2004; Evans and Kantrowitz, 2002; O’Neill et al., 2003). Studies examining the effect of air pollution on health have found higher effect sizes in low SES groups (Jerrett et al., 2004; Ponce et al., 2005; Pope, III et al., 2002). Several explanations might account for these differences: (1) higher and multiple hazardous exposures among socially disadvantaged groups cause an amplification of negative health effects and (2) biologic interaction between hazardous exposures and individual as well as contextual characteristics and behaviours lead to an increase in vulnerability (Bolte et al., 2005).

In contrast to the generally higher susceptibility of low SES groups, a lower prevalence of allergic diseases has been reported for socially disadvantaged children, even though the prevalence of environmental risk factors for allergic diseases is higher (Chaix et al., 2006; du Prel et al., 2006; Emanuel, 1988; Lannerö et al., 2002). However, severe asthma has been shown to be more prevalent in low SES groups (Heinrich et al., 1998). This raises questions regarding the validity of the results, often based on self-report, which show a positive association between high socioeconomic position and prevalence of respiratory or allergic disease in children in Germany (Heinrich et al., 1998). One possible explanation for this discrepancy may be reporting bias (Kuehni et al., 2006; Mackenbach et al., 1996). It has been hypothesised that a low parental social position is associated with a higher threshold for defining illness and that therefore self-reported morbidity might underestimate the true burden of disease in socially disadvantaged children (Mackenbach et al., 1996). Other investigators, however, did not find socioeconomic differences in responses to commonly used self-reported measures of chronic illness or found more over-reporting among lower socioeconomic groups (Heliövaara et al., 1993; Lindholm et al., 2002; Macintyre et al., 2005).

The distribution of environmental exposures and health outcomes across different social groups has been little examined in Germany. There is also a lack of knowledge concerning the effect of social position on environment–health associations. To partly fill this gap, we made use of data from a study originally designed to assess internal exposures and health effects in children living in small areas adjacent to intensive industrial activity (Krause et al., 2004; Sugiri et al., 2006).

The aim of this study was (1) to examine the associations between the different indicators of social position and environmental exposures as well as broad categories of health outcomes in children, and (2) to investigate how social position can influence environment–health relationships in an observational study.

Section snippets

Methods

We analysed data from a cross-sectional survey on 968 preschool children that was conducted in three highly industrialised districts in the Ruhr Area (Duisburg-Nord, Duisburg-Süd, Dortmund) and in one rural community (reference area: Borken) in North Rhine-Westphalia in 2000. Details of this study have been reported elsewhere (Krause et al., 2004; Wilhelm et al., 2007). It was approved by the local ethics committee. In short, children belonging to school districts within the study region were

Definition of social position

We constructed indicators of individual level social position from the database, comprising vertical as well as horizontal concepts. The child's nationality was defined non-German, if both parents were of non-German nationality. In addition to psychosocial challenges of migration, this group has potential social and political handicaps, connected with a non-German nationality.

To assess the broader concept of migration, influencing lifestyle and contextual factors without necessarily having the

Exposure assessment

Air pollutant concentrations around industrial sources display high spatial and temporal variations, depending on varying emissions, temperature, precipitation, wind strength and direction. Temporal variations were estimated from series of measurements performed since 1970. Highly resolved series of measurements on a spatial basis were performed during the study period and spatial interpolation techniques using Kriging methods applied to estimate the annual total suspended particulate matter

Outcome assessment

We defined four different categories of adverse health outcomes based on clinical or laboratory examinations and questionnaire responses. We chose broad categories to assess the general vulnerability of the children, in contrast to specific exposure–disease relationships, which were already reported elsewhere (Krause et al., 2004).

To assess allergic sensitisation (AS), patch tests (24 allergens, TRUE Test, Pharmacia, Hillerod, Dänemark), skin prick tests (inhalative allergens including pollen,

Statistical analysis

We examined the distribution of environmental exposures (TSP, ETS and ULC) according to social position with descriptive bivariate analysis. ETS and ULC were analysed as binary variables, TSP was analysed on a continuous scale and as binary variable (cutpoint >45 μg/m3) to increase sample size, because in one study region TSP concentrations were modelled only in two concentrations (⩽45 and >45 μg/m3). We calculated the crude odds ratio with 95% confidence interval (CI) for the association of

Funding

This study was funded within the “Action Program Environment and Health North Rhine-Westphalia” of the Ministry of the Environment and Conservation, Agriculture and Consumer Protection of the State of North Rhine-Westphalia in Düsseldorf, Germany and coordinated by the North Rhine-Westphalia State Agency for Nature, Environment and Consumer Protection, Germany.

Results

Three observations were excluded from the analysis due to missing information on sex, leaving 965 subjects. Table 1 displays the characteristics of the study population according to social position and area of residence. Nationality, immigration background, education, professional training, unemployment and relative poverty were distributed unequally across the four study regions, with the highest prevalence of disadvantageous social characteristics in Duisburg-Nord. With the exception of sex,

Discussion

We found strong associations between different indicators of social position and environmental exposures as well as health outcomes in this cross-sectional analysis of preschool children. Next to parental educational attainment, the most commonly used variable to describe SES, nationality, immigration background, unemployment and relative poverty were important indicators differentiating environmental exposures and health outcomes. Allergic and respiratory disease outcomes based on self-report

Acknowledgements

Our special thanks go to Mrs. Idel, Mr. Hadnagy and Mrs. Berendt, for the analysis of the immune parameters.

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