Vol. 14 •Issue 10 • Page 14
Allergy & Asthma
Children’s Age, Wheezing Determine Day Care’s Role as Factor for Asthma Development
Physicians and parents hear mixed messages about the role of day care and asthma. Research shows day care attendance to be both protective toward and a risk factor for the development of asthma. Which is true?
Multiple confounding factors contributing to asthma make it impossible to separate out day care alone in these studies, but this article will help to make sense of the confusion by reviewing the latest scientific literature.
First, let’s discuss the epidemiology of asthma and wheezing in pediatrics as this will set the basis for understanding the role of day care.
In Tucson, Ariz., researchers followed a birth cohort of children to assess the factors that affect wheezing prior to age 3 and those factors’ relationship with wheezing at age 6, thus examining the natural history of asthma in the first 6 years of life.1
The 826 children fell into four categories:
• children who have never wheezed (51.5 percent)
• children with early onset transient wheeze — wheeze prior to age 3 but not at age 6 (19.9 percent)
• children with early onset persistent wheeze — those who wheezed prior to age 3 and continued to wheeze at age 6 (13.7 percent)
• children with late onset persistent wheeze — no wheezing in first 3 years of life but wheezing at age 6 (15 percent).
The investigators also studied the children in relation to day care, and several points became clear. First, the ages of entry into day care are significant. Second, the type of wheezing (early transient, early persistent or late persistent) that the child has is important to determine if day care is a risk or protective factor.
The children who entered day care in the first 6 months of life had a 60-percent decreased relative risk of asthma at ages 5 to 14 (relative risk 0.4, P = 0.04); however, they had more wheezing at age 2 (P = 0.01).2
In terms of the type of wheezing, early entry into day care is a risk factor for early transient wheezing, yet a protective factor to late onset wheezing.
Researchers examined another group of children for the relationship between day care and asthma in Canada.3 Almost 1,000 children (half asthmatic and half controls) were evaluated at age 6 for asthma. All the children had been in day care since birth.
The same pattern emerged: Those children who attended day care prior to age 1 had a 39-percent decreased risk of persistent wheezing; however, children who had attended day care at any time prior to diagnosis had no increased risk in persistent wheezing, but more than a twofold increased risk in transient wheezing.
This study highlights the difference in timing of entry into day care and the pattern that the earlier the entry, the more protective day care is toward the development of late onset wheezing; however, the earlier the entry into day care, the more likely the child will have early transient wheezing.
Investigators conducted a similar study in Italy with more than 16,000 children.4 Children who attended day care prior to age 2 had increased risk of early transient wheezing with an increased relative risk of 1.7 (P < 0.001). These children had a 30-percent decreased risk of late-onset wheezing, though.
Another research team evaluated school-aged children (5 to 14 years) and found the later the entry into day care, the greater the prevalence of asthma.5
Day care attendance prior to 4 months old is associated with a fivefold increase risk of early transient wheezing.6 Investigators also found that the prevalence of asthma was higher among children who attended day care at an older age.7
These studies exemplify the role of day care in relation to asthma. Early day care is a risk factor for early transient wheezing and protective for late onset wheezing.
A POSSIBLE EXPLANATION
So what’s the proposed reason for the protective effect of day care in relationship to the development of late onset wheezing?
It’s thought that children who enter day care early in life have more respiratory illnesses that help to alter the ratio of T helper cells. During pregnancy, Th2 is important in a successful pregnancy, but later in life it’s associated with allergic disorders such as asthma.8
The more a child is exposed to “germs,” the more the body makes Th1 cells that inhibit Th2 cells and thus decrease allergic complications, including asthma.9,10
Endotoxin, which is a component of the cell wall of gram negative bacteria, is also abundant in day care settings where there are multiple children as well as dust and rugs.11 Increased exposure to endotoxin is associated with decreased allergen sensitization and atopic asthma in children.
In summary, day care is both a risk factor and a protective factor for the development of asthma or wheezing. Early entry into day care causes an increased risk of early transient wheezing; however, it protects individuals against late onset wheezing beyond the age of 3.
Does this mean that if you were to have your child in day care from an early age, they wouldn’t have asthma when they were older?
The answer is that they have a decreased risk, but there are too many components to the etiology of asthma, such as family history of atopy, maternal history of asthma, and exposure to tobacco smoke, to know for sure.
Adrienne Prestridge, MD, is a pediatric pulmonologist at Children’s Memorial Hospital in Chicago where she’s the associate director of the cystic fibrosis center and the director of the pulmonary function lab.
For a list of references, please call Mike Bederka at (610) 278-1400, ext. 1128, or visit www.advanceweb.com/respmanager.
• Day care is common: Sixty percent of preschool children attended day care in 1995, with 7 percent of children younger than 1 year old and 65 percent of children at age 4 having attended day care.3
• Asthma is the leading cause of childhood illness and disability, with increasing burden over the past two decades. Children ages 0 to 17 have had increases in prevalence, hospitalization and mortality due to asthma at an average of 4.3 percent, 1.4 percent and 3.4 percent per year, respectively, from 1980 to the late 1990s.12