Early Childhood Weight Linked to Later Lung Function

Analysis of CF registries in the U.K. and Canada explores association

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by Steve Bryson, PhD |

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Higher weight in children with cystic fibrosis (CF) at 1 year of age, and increasing weight gain from ages 1 through 5, were correlated significantly with better lung function at age 6, according to an analysis of two large  registries.

Current guidelines may need to be updated to encourage tracking of weight over time, as well as weight in early infancy, to guide ongoing clinical CF care, the researchers suggested.

The CF registry analysis was published in the study “Trajectories of early growth and subsequent lung function in cystic fibrosis: An observational study using UK and Canadian registry data,” in the Journal of Cystic Fibrosis.

One of the complications of CF is a lack of digestive enzymes secreted by the pancreas, which can lead to reduced nutrient absorption and an increased risk of malnutrition. Importantly, low weight in CF has been linked with poor lung function, pulmonary exacerbations, and lung transplant.

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In CF children, maintaining a proper weight at certain ages (weight-for-age) and gaining weight during development is vital in managing overall health in CF.

Current guidelines recommend extra monitoring or nutritional intervention, such as oral supplementation, when a CF child’s body mass index (BMI, a measure of body fat), falls below the 10th percentile of a healthy population (at a given age). Maintaining a BMI above the 50th percentile is commonly recommended.

Understanding whether nutritional status in the early years of growth in CF children affects lung function later on may help inform healthcare professionals on how to use nutritional assessment to guide clinical care.

Researchers in the U.K. analyzed data from two large CF registries in the U.K. and Canada to explore an association between weight changes in CF children ages 1 through 5 and lung function at around age 6.

Data included 1,974 CF children in the U.K. and 791 in Canada. Participants’ characteristics in both datasets were similar except for presentation at diagnosis, whereby 48.1% of the U.K. group were asymptomatic at diagnosis compared to 25% of the Canadian group. The number of those diagnosed by newborn screening also was higher in the U.K. group.

The team converted body weights measured over time to weight-for-age z-scores, defined as the difference between a CF child’s weight at a certain age and healthy growth reference values.

BMI at a specific age (BMI-for-age) was included, as were lung function tests, such as forced vital capacity (FVC), the total amount of air exhaled from the lungs, and FEV1, the amount of air forced from the lungs in one second.

According to the analysis, the average weight-for-age trajectories (changes over time) from age 1 to 5 did not change at an equal rate (non-linear). Small increases were seen up to about 2.5 years, after which z-scores for weight-for-age and BMI leveled off and remained close to zero, or no differences between CF children and typical values.

Notably, there were large variations in weight among CF children at the age of 1, as reflected by z-scores ranging from −4 to 2.5.

Canadian, UK data concur

Canadian and U.K. data both indicated that, after adjusting for age, children who weighed more at 1 year had significantly better lung function later on. Every increase in one weight-for-age z-score was associated with a rise of 3.78 FEV1% (of normal) in the U.K. data and 3.20 FEV1% in the Canadian dataset. Children whose weight-for-age z-score increased over time had significantly better lung function at age 6.

Results for FVC% were similar. An increase in the z-score of weight at age 1 was related to about a 4.0 FVC% improvement at nearly 6 years. Changes in weight-for-age over time also were associated with later FVC%, but the association was weaker.

For BMI, an increase of one BMI- z-score at the age of 1 year correlated with a rise of 4.13 FEV1% in the U.K. and 3.70 FEV1% in Canada. However, only in U.K. patients did increasing BMI z-scores over time correlate with better FEV1% values later on.

Similar findings were seen after adjusting for factors that may influence the results (confounders), including sex, birth year, economic status, pancreatic insufficiency, genetic defects, and age and clinical status at diagnosis.

“Although we cannot comment on the causal relationship, our individualized trajectory approach suggests that, amongst [CF children] with similar nutrition at age 1, there is a risk of lower lung function at age 6 years if their weight-for-age is not maintained,” the researchers wrote.

“Current guidelines may need to be updated to place less emphasis on a specific cut-off (such as the 10th percentile),” the researchers concluded, and “encourage clinical tracking of weight-for-age over time, as well as weight-for-age in early infancy.”

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