An abnormal BMI in children—be it high or low—can now be associated with impaired lung function, but if their BMI is normalized before they reach adulthood, the impairment can be offset, researchers from Karolinska Institutet report.

Their results, which are based on data collected under the BAMSE project in Sweden, are presented in The European Respiratory Journal in a paper titled “Body mass index trajectories from birth to early adulthood and lung function development.”

One in 10 people have reduced lung function development in childhood and cannot achieve maximal lung capacity in adulthood, increasing the risk of serious health problems such as cardiovascular disease, lung disease and diabetes. One risk factor associated with impaired lung function development is abnormal weight and height. The most common body measurement, BMI (body mass index), takes account of weight, but not muscle and fat composition.

Previous studies have looked into the correlation between BMI and lung function with varying results. Swedish researchers now demonstrate that a correlation does indeed exist when the BMI deviates from the normal—in either direction.

“In this study, the largest so far, we’ve been able to follow children from birth all the way to the age of 24, covering the entire period of lung function development,” says the study’s first author Gang Wang, researcher at the Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet.

Early intervention is important

The participants could be divided up into different BMI groups, which had already begun to differentiate themselves by the age of two. Unlike children with a normal BMI, those with a persistently high BMI or an accelerated increasing BMI had impaired lung function as adults, primarily the result of restricted airflow in the lungs, a condition known as obstruction.

“Interestingly, we found that in the group with an initially high BMI but a normalized BMI before puberty, lung function was not impaired in adulthood,” says principal investigator Erik Melén, professor of pediatrics at the same department at Karolinska Institutet and doctor at the Sachs’ Children and Youth Hospital.

“This highlights how important it is to optimize children’s growth both early in life and during their early school years and adolescence.”

A stable low BMI could also be linked to reduced lung function caused by inadequate lung growth. In these cases, BMI was not normalized over the course of the study.

“The focus has been on overweight, but we also need to capture children with a low BMI and introduce nutritional measures,” says Dr. Wang.

Analyzing large volumes of BMI data

The study was based on the BAMSE project, in which over 4,000 children have been followed from birth to the age of 24. BMI has been repeatedly measured over this time, at most 14 times. The present study includes 3,200 participants with at least four BMI measurements.

Lung function was measured using spirometry at the ages of 8, 16 and, finally, 24, at which point the function of the smaller airways was also measured via the volume of exhaled nitrogen. Urine samples were also taken so that an analysis of the substances being metabolized could be performed in collaboration with docent Craig Wheelock at Karolinska Institutet’s Institute of Environmental Medicine.

Objective biomarkers

The urine samples from the high BMI group showed elevated levels of metabolites of the amino acid histidine, corroborating the observations of other researchers who found a similar increase in patients with asthma and chronic obstructive pulmonary disease.

“We see here objective biomarkers for the correlation we’ve found, even if we don’t yet know exactly the molecular association between high BMI, histidine and impaired lung development,” says Professor Melén.