Does impaired lung function in childhood stay impaired?
Roughly a third to a half of children with impaired spirometry recovered normal lung function by early adulthood, and weight and maternal smoking predicted who did not.
Source
Obstructive and restrictive spirometry from school age to adulthood: three birth cohort studies
Study at a glance
- Design
- Cohort — Pooled individual-level data from three UK population-based birth cohorts, with at least three spirometry measures per participant from childhood to early adulthood
- N
- N=8404 · 8404 at mid-school (8–10 years), 5764 in adolescence (15–18), 4680 in early adulthood (20–26); numbers fall across waves as cohorts attrit
- Population
- UK birth-cohort participants recruited 1989–1995, over 95% of white European ancestry
- Outcome
- Movement between normal, obstructive and restrictive spirometry phenotypes across two age transitions
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What they did
The authors pooled individual participant data from three UK birth cohorts set up between 1989 and 1995, keeping participants who had spirometry at least three times between school age and their twenties. Rather than using external reference equations, they classified each person as normal, obstructive or restrictive using regression residuals adjusted within the pooled sample. They then examined two transitions — 8–10 to 15–18 years, and 15–18 to 20–26 — using both regression models and data-driven clustering.
What they found
About 10% of participants showed an obstructive pattern and about 9% a restrictive one. Impairment was often not permanent: between a third of obstructive and a half of restrictive children moved into normal, stable lung function by early adulthood. Movement in the other direction was rarer, with under 5% of school-age children with normal lung function declining by adulthood. Being underweight with restriction, or obese with obstruction, made a return to normal less likely, and maternal smoking in pregnancy and a current asthma diagnosis raised the risk of persistent obstruction.
The limits
What it doesn't show
This is observational, so none of the associations establish that changing weight or smoking would change lung function. Phenotypes were defined by regression residuals internal to these cohorts rather than standard reference equations, which the authors note limits how far the categories generalise. Over 95% of participants were of white European ancestry, so the results are explicitly not transferable to other ethnic groups. Only pre-bronchodilator spirometry was available, and no preschool lung function was measured, leaving the earliest period unobserved.
Key terms
- Spirometry
- A breathing test that measures how much air a person can blow out and how fast; this study used measurements taken before any bronchodilator medicine.
- Obstructive pattern
- Air comes out more slowly than expected for the lungs' size, the pattern typical of narrowed airways.
- Restrictive pattern
- The lungs hold and move less air than expected, while the rate of airflow relative to size is preserved.
- Birth cohort
- A group of people followed from birth with repeated measurements; here, three UK cohorts set up between 1989 and 1995.
- Regression residual
- How far a person's measurement sits from what the model predicts for someone like them; the authors used these, adjusted within the pooled sample, instead of external reference equations to label each person.
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Common questions
Does an impaired spirometry result in childhood mean lifelong impairment?
Not usually in these cohorts. Between a third of children with an obstructive pattern and half with a restrictive pattern moved into normal, stable lung function by early adulthood.
How often did normal lung function in childhood decline?
Rarely. Under 5% of school-age children with normal lung function had declined by adulthood.
What predicted staying impaired?
Being underweight with restriction, or obese with obstruction, made a return to normal less likely. Maternal smoking in pregnancy and a current asthma diagnosis raised the risk of persistent obstruction.
Does this show that changing weight or avoiding smoking would improve lung function?
No. The study is observational, so these are associations, not evidence that changing them would change lung function.
Who do the results apply to?
Over 95% of participants were of white European ancestry, and the authors say the results are not transferable to other ethnic groups. The categories also came from residuals within these cohorts, which limits how far they generalise.
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