Differential impact of low fat-free mass in people with COPD based on body mass index classifications: results from COSYCONET

Science and Research

BACKGROUND: Alterations in body composition, including a low fat-free mass index (FFMI), are common in patients with chronic obstructive pulmonary disease (COPD) and occur regardless of body weight. RESEARCH QUESTION: Is the impact of low FFMI on exercise capacity, health-related quality of life (HRQL) and systemic inflammation different among COPD patients stratified in different body mass index classifications? STUDY DESIGN AND METHODS: We analysed baseline data of COPD patients from the COSYCONET (COPD and Systemic Consequences - Comorbidities Network) cohort. Assessments included lung function, bioelectrical impedance analysis, six-minute walk distance (6MWD), HRQL and inflammatory markers. Patients were stratified in underweight (UW), normal weight (NW), pre-obese (PO) and obese (OB) according to BMI and as presenting low, normal or high FFMI using 25(th) and 75(th) percentiles of reference values. Linear mixed models were used to investigate the associations between FFM and fat mass with secondary outcomes in each BMI group. RESULTS: 2137 COPD patients (GOLD 1-4, 61% males, age: 65±8years, FEV(1): 52.5±18.8%pred) were included. The proportions of patients in UW, NW, PO and OB groups were 12.3%, 31.3%, 39.6%, 16.8%. The frequency of low FFMI decreased from lower to higher BMI groups (UW:81%, NW:53%, PO:42%, OB:39%). FFM was associated with the 6MWD in the UW group, even when adjusting for a broad set of covariates (P<0.05). HRQL was not associated with FFM after adjustment for lung function or dyspnea (P>0.32). Fat mass was associated with higher systemic inflammation in the NW and PO groups (P<0.05). INTERPRETATION: In patients with COPD with lower weight, such as UW patients, higher FFMI is independently associated with better exercise capacity. In contrast, in PO and OB COPD patients, a higher FFMI were not consistently associated with better outcomes.