Some infants and toddlers have asthma symptoms when they catch colds and viruses but by the time they are three years old, they are wheeze−free, even when sick. Other children are fine during the first few years but develop wheezing sometime after their third birthday. Still others wheeze as infants and toddlers and continue having asthma symptoms into childhood. What determines whether a child will grow into or out of asthma? A recently published study in the December issue of the Journal of Pediatrics explored this question.

Asthma is the most prevalent chronic childhood disease in the United States. It afflicts more than 9 million children and it is on the rise. Doctors wonder why. One study showed that children who catch fewer infections as young children are more likely to develop a condition called atopy, which is the tendency to develop allergic/inflammatory reactions such as those which cause asthma. It has also been suggested that being exposed to fewer children during early childhood has led to an increase in atopy, possibly because exposure to fewer children means sharing fewer colds and viruses. Studies have also shown that children who attend daycare in early childhood have fewer allergies and less asthma than those who don't. And still other studies have also shown that attendance at daycare increases the number of respiratory infections a child catches. How do these all fit together?

When considering day care settings, [parents] may also want to consider the evidence that toddlers who are exposed to more children have a lowered risk of asthma than their more isolated peers.

Wheezing/asthma in childhood is divided into three main types:

  • children who only wheeze with respiratory infections during their first three years
  • children who don't wheeze until they are older than three years
  • children whose wheezing/asthma begins before three and continues throughout childhood.

Ironically, while studies have shown that attending day care increases the risk of wheezing/asthma in children younger than 5 years, they also show that daycare attendance protects against the development of asthma in older children. To investigate this paradox further, researchers looked at whether the number of children one was exposed to during early childhood affected one's risk for either having early childhood asthma symptoms which didn't go away, or for newly developing asthma after age three.

The investigators followed 939 children from birth through age 15 years. They obtained information about their childcare settings including the number of other children present and the number of hours each spent in daycare. They took into account other known risk factors for asthma, including maternal education, age, and smoking habits, whether the child was breastfed, and how often the child had respiratory infections. At preset intervals throughout the study period, they asked about the occurrence of asthma/wheezing symptoms.

The researchers found that by age 15 years, 3% of the study population had asthma that had persisted since before age three years, and 16% had developed later−onset (starting older than three years) asthma. When they asked whether those children with asthma had had more children in their daycare settings, they found that while being around more children during infancy didn't seem to impact asthma risk, the number of children in the childcare environment during toddlerhood (16−36 months) made a significant difference.

Children who as toddlers were exposed to few or no children had a higher risk of persistent or late onset asthma than those with more exposure. As the number of day care attendees increased, the risk of asthma went down, although the positive effect slowly leveled off and then stopped at nine attendees. They concluded that exposure to other children in daycare settings during the toddler years may protect against the development of asthma. However, this protection appeared to level off when the number of children increased beyond a certain limit. In addition, when they looked at how often the asthmatic children had been ill as toddlers, they learned that there was more to the positive effect of being exposed to other children in daycare than getting sick more often. They proposed that other environmental exposures that are associated with groups of toddlers in daycare might also play a protective role.

Parents of children who develop wheezing illnesses should always consult with their children's doctors about the best treatments for them. Parents may take heart from the information that not all children who wheeze with early illnesses continue on to develop chronic asthma, and that studies have shown that exposure to infections during toddlerhood may play some role in preventing later illnesses, including asthma. When considering day care settings, they may also want to consider the evidence that toddlers who are exposed to more children have a lowered risk of asthma than their more isolated peers. They may wish to discuss the pros and cons of various day care settings with their children's doctors, and should also consider their child's health and temperament when assessing the suitability of the daycare environment.