Childhood Asthma

Childhood Asthma Followed to Adulthood

What is the problem and what is known about it so far?
Asthma is a chronic condition with acute episodes of reversible constriction of the airways of the lung. People who suffer from asthma have airways that are hypersensitive to various environmental triggers that cause inflammation in the lung.  These triggers include cigarette smoke, air pollution, and house dust mites. Sometimes cold, stress, and exercise can also set off asthma attacks. Most attacks involve severe shortness of breath, coughing and wheezing. They occur from time to time, last for a short period and then get better. However, under some conditions, asthma can be fatal. In 2001 20.3 million Americans reported having asthma. Of these, 6.3 million were under the age of 18. Although considerable progress has been made in the treatment of asthma symptoms, there are no proven ways to prevent the disease. Thus more research is being directed toward improving our understanding of how asthma begins and what causes it to continue so new preventive approaches may be developed.

Why did the researchers do this particular study?
Past studies have relied heavily on patients' recall of events in early childhood. Not surprisingly, this approach had limitations as most adults have no direct memory of their preschool years. Based on these studies it was widely believed that chronic asthma was equally likely to begin at any age. Also, these studies led to the belief that the environmental triggers of the asthma symptoms also caused asthma. The researchers of this study took a different approach. They wanted to identify possible factors that could affect how long a person continued to have asthma attacks and how often they occurred in the general population, rather than in a group who were already known sufferers of asthma.

Who was studied?
Children born in a province in the South Island of New Zealand between April 1972 and March 1973 formed the study group. The children came from various socioeconomic backgrounds and were mostly of European descent.

How was the study done?
Ninety one percent of the children born in this period were seen at age 3 years. All were then seen every 2 or 3 years for tests until age 26. The tests included questionnaires, lung function tests, bronchial-challenge tests (to test for airway hyperresponsiveness), and allergy tests. At age 9, an accompanying adult answered detailed questions regarding the child's respiratory history between birth and age 9. Subsequently, the children answered the questionnaires.

What did the researchers find?
613 out of the original 1037 children had results from all the tests so this group provided the study results.  73 percent of this group reported one and 51 percent more than one, episode of wheezing by age 26. Over one quarter still had symptoms of asthma at age 26. Of this group, just over half had persistent wheezing from onset with no remission and just under half went into remission but then relapsed. Allergy to house dust mites and airway hyperresponsiveness influenced those with persistent wheezing and those who got better and then relapsed. Smoking at age 21 and being female was more common in those who had persistent wheezing. Relapse was more likely in those whose wheezing started at an early age. In both groups, lung function was lower than normal at each assessment during childhood, adolescence, and adulthood.

What were the limitations of the study?
Because the participants were only followed until 26 years of age, the number of remissions may have been overestimated (some people may stop having symptoms at an older age) and also the number of relapses may have been underestimated (some people may relapse at an older age). Another limitation of the study is that the histories of symptoms were obtained when the children were already 9 years old. Therefore, the study's findings are limited to children whose mothers recalled symptoms during that time. It is possible that episodes of mild wheezing had occurred during this time period but were not recalled because they were not serious enough to be recognized.

What are the implications of the study?
Adults suffering from either persistent or relapsing-remitting asthma have lower than normal lung function throughout childhood, adolescence, and adulthood. This reduction in lung function is determined early in childhood. Therefore, successful strategies to prevent loss of lung function in people with asthma will need to focus on young children as the disease process is beginning.

Submitted by Stanley Kang, College of Medicine, University of Vermont
Summarized from "A Longitudinal, Population-Based, Cohort Study of Childhood Asthma Followed to Adulthood". Sears MR et al.  The New England Journal of Medicine, October 9, 2003, Volume 349, Issue 15, Pages 1414-1422.