The relationship between insulin, IGF‐I and weight gain in cystic fibrosis

OBJECTIVE In cystic fibrosis, reduced body mass is related to low levels of IGF‐I and changes in the IGF binding proteins. Our aim was to determine whether these abnormalities are linked to pancreatic endocrine dysfunction. PATIENTS AND DESIGN We measured serum levels of insulin, IGF‐I, IGFBP‐I, IGFBP‐3 and IGF bioactivity in 77 fasting subjects (43 male) mean age 9.6 years (range 2.99–17.98 years). Data were analysed with respect of body mass, puberty and stature and compared with control data established in the same laboratory. RESULTS The mean height standard deviation score (SDS (SD)) was −0.54 (0.97) and the body mass index SDS −0.24 (1.09). Both body mass index SDS ( r  = −0.40, P  = 0.0003) and IGF‐I SDS ( r  = − 0.32, P  = 0.009) declined with age. Insulin levels were also low and correlated with IGF‐I and IGFBP‐3 ( r  = 0.42, P  = 0.0004, and r  = 0.45, P  = 0.0002, respectively) whereas levels of IGFBP‐I were inversely related to those of IGF‐I and insulin ( r  = − 0.43, P  = 0.0004, r  = − 0.52, P  < 0.0001). IGF bioactivity was reduced and inversely related to IGFBP‐I ( r  = − 0.31, P  = 0.009). In multiple regression analysis, body mass index SDS was negatively related to age ( P  < 0.0001) and positively related to insulin and IGF‐I ( P  = 0.04, P  = 0.03, respectively). Height SDS was correlated with IGF bioactivity ( P  = 0.003) and negatively with IGFBP‐I ( P  = 0.01). CONCLUSIONS We conclude that progressive insulin deficiency may result in reduced IGF‐I levels and IGF‐bioactivity and may determine weight gain and statural growth in cystic fibrosis.