Loss of fat-free mass over four years in adult cystic fibrosis is associated with high serum interleukin-6 levels but not tumour necrosis factor-alpha

Background aims: Malnutrition is associated with poorer outcome in cystic fibrosis (CF). This follow-up study aimed to document nutritional status changes, including fat-free mass (FFM), in adults with CF; and to identify predictors of FFM loss. Methods: Fifty-eight non-transplanted CF adults (mean ? SD forced expiratory volume in one second (FEV1) 63.7 ? 21.4 predicted; mean ? SD age 30.3 ? 7.7years at baseline) were studied at baseline and 3.6 ? 0.4 years later. Body composition was measured using dual-energy X-ray absorptiometry. At follow-up, blood was analysed for interleukin-6 and tumour necrosis factor-a (TNF-a) on three occasions over six months and averaged for each participant. Associations with annual percentage change in FFM (ann ?FFM), including cytokines, CF genotype and annual change in FEV1 predicted (ann?FEV1 ), were determined. Results: Mean FFM was 49.5 ? 8.8 kg at baseline and 49.6 ? 8.9 kg at follow-up (p = 0.66). Ann ?FFM ranged from -2.0 to +3.6 . FEV1 predicted declined by 1.2 ? 2.4 per year. Forty percent of participants had elevated average interleukin-6 levels. Ann ?FFM was negatively correlated with interleukin-6 levels (rho -0.34, p = 0.008), but not TNF-a or ann?FEV1 . F508DEL homozygote or heterozygote participants had greater FFM loss than those carrying no F508DEL allele (p = 0.01). Conclusion: Higher serum interleukin-6 and presence of the F508DEL mutation, but not TNF-a, were associated with FFM loss in adults with CF