For a study, it was determined that in contrast to the well-known link between early-life weight for age, BMI, and later lung disease in patients with cystic fibrosis (CF), the link between height-for-age (HFA) percentiles and respiratory morbidity received less attention. Changes in HFA throughout the first 6 years of life in children with CF would be linked to pulmonary function at the age of 6–7 years. In the final cohort analysis of children with CF born between 2003 and 2010, CF was diagnosed before two years and followed for at least seven years in the CF Foundation Patient Registry. Changes in annualized HFA were divided into two mutually exclusive groups. At the age of 6–7 years, researchers employed multivariable analysis of covariance models to see if there was percent-predicted forced expiratory volume in 1 second (FEV1) and height-trajectory categories. 

The CF Foundation Patient Registry has 5,388 eligible children. At the age of 6–7 years, the median (interquartile range) HFA was in the 39.5th (17.2th–64.9th) percentile. At 6–7 years, the mean (95% CI) FEV1 % expected was 95.6% (95.1–96.1%). In a multivariable regression model, the mean (95% CI) predicted FEV1% was higher for children with HFA that was always above the 50th percentile (97.8% [96.3–99.4%]) than for children whose height had been below the 50th percentile for at least 1 year and increased by ten percentile points (95.1%[93.7–96.6%]), was stable (94.3% [92.8–95.7%]), or decreased by ten percentile. Adding the mean annualized BMI percentile at the age of 6–7 years to the regression model did not affect the link between HFA categories and FEV1% predicted. There was a link between the nadir annualized HFA percentile and the FEV1% projected at the age of 6–7 years among those with HFA that reduced by ten percentile points. At the age of 6–7 years, children with CF who have HFA above the 50th percentile have the best pulmonary function. Maintaining a BMI above the 50th percentile is an important aim for children with CF, but it is not the only criterion to consider when assessing nutrition.