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In a New Zealand birth cohort study (
) almost three quarters of the subjects (72.6%) had significant wheezing at some time in childhood and more than a third (37%) of these (27% of the cohort) wheezed as young adults. Impairment of lung function in persistent wheezers dated from before the age of 9 years and did not get worse by early adult life.
A total of 1139 children were born in Dunedin between April 1972 and March 1973 and still lived in the province of Otago when they were 3 years old. Of these children 1037 entered the study as 3-year-olds and complete study data to the age of 26 years was obtained for 613. They were followed up every 2 years to age 15 and at ages 18, 21, and 26 years. Data from questionnaires and from tests of lung function, bronchial responsiveness, and allergy were collected from the age of 9 years.
By the age of 26 years only 168 of the 613 subjects (27%) had never reported wheezing that occurred more than once or twice a year and lasted more than an hour. Half (315 of 613) had reported wheezing on two or more visits. Wheezing was persistent from onset in childhood to age 26 in 89 (14.5%). It had remitted in 168 (27%) but subsequently relapsed in 76 (12.4% of the analysed cohort, 45% of remitters). Between the ages of 9 and 26 the line of the graph of FEV1: FVC for persistent wheezers remained parallel to but below that for nonwheezers. Factors associated with wheezing at age 26 years (persistence or relapse) were female sex, house dust mite sensitisation, bronchial hyperreactivity, and smoking at age 21 years. Early age of onset was associated with higher risk of relapse, each year of delay in onset reducing the risk of relapse by 11%. Relapse after the age of 26 is thought to be uncommon.
Wheezing in childhood is common but about two thirds of children who ever wheeze no longer do so as young adults. Persistent wheezers already have impaired lung function at age 9 years but the degree of impairment does not increase. The origins of asthma are in early childhood.