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Table 1 Birth cohort studies

From: Does traffic exhaust contribute to the development of asthma and allergic sensitization in children: findings from recent cohort studies

Study Study population Age Exposure assessment Agent Range of exposure Outcome Relative risk Comments
Gehring et al 2002 Birth cohort (GINI and LISA), 1756 children in the city of Munich 1–2 yrs Individual exposure estimated from regression models
Annual mean at birth
NO2, PM2.5 20–67 μg/m3
12–22 μg/m3
Questionnaire-reported symptoms Slightly increased OR of non-specific respiratory symptoms, significant only in males Adjustment for important confounding variables
Morgenstern et al 2007 Birth cohort (GINA and LISA), 3577 children from the city of Munich and surrounding area 1–2 yrs Individual exposure estimated from regression models and buffer zones variables. NO2, PM2.5 19–72 μg/m3
7–15 μg/m3
Annual mean at birth
Questionnaire-reported symptoms Distance to nearest main road less than 50 m, OR 1.23 (1.00–1.51) for asthmatic bronchitis
Very few children with doctor-diagnosed asthma at this age
Adjustment for important confounding variables
Morgenstern et al 2008 Birth cohort (GINA and LISA), 3066 children from the city of Munich and surrounding area 6 yrs Individual exposure estimated from regression models and buffer zones variables NO2, PM2.5 6–74 μg/m3
19–13 μg/m3
Average exposure up to 6 years of age.
Questionnaire-reported symptoms
Circulating IgE
Distance to nearest main road less than 50 m:
OR 1.66 (1.01–2.59) for doctor-diagnosed obstructive bronchitis or asthma
OR 1.30 (1.02–1.66) sensitization to pollen
Adjustment for important confounding variables.
Blood samples were obtained from 1353 children (an unspecified subset) – the loss in retention rate is not commented
Brauer et al
2002
Birth cohort (PIAMA) from the Netherlands, 4,146 children at start, 3,745 at one year and 3,730 at 2 yrs. 2 yrs Individual exposure estimated from regression models NO2, PM2.5 13–58 μg/m3
13–25 μg/m3
Annual mean at birth
Questionnaire-reported symptoms Slightly but significant increased risk of upper respiratory infections Adjustment for important confounders.
Brauer et al 2007 Birth cohort (PIAMA) 3,538 children
(retention 85%)
A subgroup of 713 children
4 yrs Individual exposure estimated from regression models NO2, PM2.5 13–58 μg/m3
13–25 μg/m3
Annual mean at birth
Questionnaire-reported symptoms
Circulating IgE
OR for IQR of PM2.5 1.32 (1.04–1.69) for doctor-diagnosed asthma ever and 1.75 (1.23–2.47) for any sensitization to food allergens Adjustment for important confounders.
High rate of retention
High risk children were overrepresented in the IgE screening subgroup
Low rate of sensitization to outdoor allergen
Nordling et al 2008 Birth cohort (BAMSE) of 4,089 children in Stockholm, Sweden
3,515 replied to questionnaires at 4 yrs and 2,543 delivered blood samples
4 yrs Individual exposure based on atmospheric dispersion model, high resolution NOx, Traffic PM 5–49 μg/m3
1–7 μg/m3
(P5–P95)
Annual mean at birth
Questionnaire-reported symptoms
Circulating IgE
OR for 95th % range of NOx 1.60 (1.09–2.36) for persistent wheeze and 1.67 (1.10–2.53) for any sensitization to pollen Adjustment for important confounders.
Analyses based on exposures during 1st year of life
Significant difference between extreme percentiles of exposure. Dose-response relations not presented.
Melén et al 2008 Case-cohort within the BAMSE birth cohort in Stockholm (a randomly sampled subcohort of 542 nonwheezers and 167 wheezers. In addition 375 wheezers from the original cohort) 4 yrs Individual exposure based on atmospheric dispersion model, high resolution NOx,   Questionnaire-reported symptoms
Circulating IgE
Variants in the GSTP1 and TNF genes modify the association between sensitization and NOx.  
Oftedal et al 2008 Birth cohort study in Oslo, Norway
2,244 children who lived in Oslo since birth
10–11 yrs Individual exposure based on atmospheric dispersion model with contributions from busy roads NO2, PM2.5
PM10
Mean (IQR) life time estimate
29.0 (19.5) μg/m3 NO2 and 12.3 (3.6) μg/m3 PM2.5
Smaller ranges compared to Nordling et al
Skin prick test No association between long-term exposure and sensitization to any allergen (except for D. farinae) Very few children were sensitized to D farinae and the association with traffic exhaust was likely to be caused by confounders
Ryan et al 2005 Birth cohort study (the Cincinnati Childhood Allergy and Air Pollution Study, CCAAPS) – 622 children with at least one allergic parent were enrolled at 6 months 1 year Individual exposure (distance to various traffic conditions) based on GIS model   Not recorded Questionnaire-reported wheeze without a cold Distance to stop-and-go traffic less than 100 m: OR 2.5 (1.15–5.42) for wheezing without a cold
No effect from smoking
A small study with limitations in the control of confounding
Ryan et al 2007 CCAAPS
See above!
1 year Individual exposure (distance to various traffic conditions) based on GIS model and regression model estimating elemental carbon attributable to traffic ECAT 0.30 – 0.90 μg/m3 Questionnaire-reported wheeze without a cold Significant exposure-response association between ECAT level and risk of wheeze The strength of this study is the improved exposure assessment
Clougherty et al 2007 Birth cohort – 888 pregnant women were enrolled and the caregivers of 417 children responded to questionnaires after 6–10 yrs ~7 yrs Individual exposure based on a regression model NO2 38–85 μg/m3 Frequent telephone or face-to-face-interviews OR for 8 μg/m3 increase in NO2 exposure 1.63 (1.14–2.33) for diagnosed asthma but only in children exposed to violence. NO2 was included as a continuous variable. Concentration at the year of diagnosis showed the closest association.
Limitations: Low retention rate, reporting bias and potential confounding