Early-life environmental risk factors for asthma: findings from the children's health study - Children's Health

Environmental Health Perspectives, May, 2004 by Muhammad Towhid Salam, Yu-Fen Li, Bryan Langholz, Frank Davis Gilliland

Compared with never-exposed children, children exposed to herbicide and pesticide in the first year of life were significantly at higher risk of asthma, with ORs of 4.58 and 2.39, respectively (Table 3). Exposure beginning after the first year was not associated with increased risk of asthma. When pesticide and herbicide exposures were considered together, children exposed to any pesticide or herbicide in first year of life were at 2.53-fold higher risk of asthma compared with children who were never exposed to either of those (OR = 2.53; 95% CI, 1.25-5.09). The ORs for the association of exposure to herbicide and pesticide and early persistent asthma were largest for exposure beginning in first year of life (OR = 3.78; 95% CI, 1.70-8.41). Adjustments for exposure to the farm environment did not substantially change the estimates for herbicides and pesticides.

Exposure to farm animals, farm crops, or dust was associated with increased risk for asthma (Table 4). Compared with never-exposed children, those who were ever exposed to farm animals, farm crops, or dust had a 60% increased risk of asthma (OR = 1.60; 95% CI, 1.01-2.52). The risk was larger in children who had these exposures in their first year of life than in those who were exposed thereafter (OR = 1.88 vs. 1.32); however, this difference was not statistically significant. In subset analyses, children with exposures to farm animals and farm crops/dust had elevated ORs for both early transient wheezing and early persistent asthma; however, only the ORs for the latter category reached statistical significance. Early persistent asthma was statistically significantly associated with exposure in first year of life to farm animals (OR = 3.03; 95% CI, 1.00-9.17) and farm crops/dust (OR = 2.06; 95% CI, 1.02-4.15). Inclusion of herbicides and pesticides exposure status in the regression models did not change the effect estimates for the farm environment.

Sibship size at the time of birth was inversely associated with asthma risk ([P.sub.trend] = 0.01; Table 5). Children who had four or more sibs were at 63% reduced risk of asthma (OR = 0.37; 95% CI, 0.18-0.77) compared with children with one sib. Notably, children with no siblings were at lower risk than were children with one sibling. These associations were independent of day care attendance. We observed a weaker association of asthma with maternal parity than sibship size (data not shown). Effect of sibship size did not vary substantially by asthma categories.

Day care attendance itself was positively associated with early childhood asthma (Table 5). Compared with children who never attended day care centers, those who went to such a center had a 1.6 times higher risk of developing childhood asthma (OR = 1.60; 95% CI, 1.07-2.39). This increased risk was highest when day care attendance occurred before 4 months of age (OR = 2.42; 95% CI, 1.28-4.59). Although risk was increased in all three disease categories, the ORs were stronger for early transient wheezing. Day care attendance before 4 months of age was associated with more than 5-fold increased risk of early transient wheezing (OR = 5.36; 95% CI, 1.33-21.50). Attending day care centers after 1 year of age also increased the risk of early transient wheezing (OR = 3.27; 95% CI, 1.26-8.48).