Background and objectives: Patients with chronic obstructive pulmonary disease (COPD) often have alterations in body weight and composition. Lower vitamin D status is more common in patients with COPD compared to controls and have been related to muscle atrophy and impaired musculoskeletal function. Therefore, we aimed to investigate the relationship between 25-hydroxyvitamin D (25(OH)D) and body composition (BC), as well as longitudinal changes in BC, in patients with COPD and controls. Methods: Patients with COPD and controls participating in the Individualized COPD Evaluation in relation to Ageing (ICE-Age) study, a Dutch prospective observational study, were included. Plasma 25(OH)D was assessed at baseline using radioimmunoassay, and values <50 nmol/L were referred to as insufficient. BC was measured using dual X-ray absorptiometry, at baseline and after two years. Multiple linear regression analyses were performed to assess the relationships between 25(OH)D (nmol/l) and longitudinal changes in BC. Means ± standard deviations are shown, unless otherwise stated. Results: In total, 192 patients with COPD, age 62 ± 7 years and 199 controls, age 61 ± 7 years, were included. Plasma 25(OH)D was lower in patients with COPD (64 ± 26 nmol/L) compared to controls (75 ± 25 nmol/L), p < 0.001, despite a higher proportion of patients reported vitamin D supplement use (15% vs 2%), p < 0.001. Bone mineral density (BMD) at proximal femur and lumbar spine was significantly lower in patients with COPD compared to controls (p < 0.001). Both patients and controls had significant declines in fat-free mass index (FFMI) (–0.4 ± 0.8, p < 0.001 vs –0.1 ± 0.5 kg/m², p = 0.002 respectively) and T-score hip (median –0.1 (–0.5 – 0.2), and –0.1 (–0.4 – 0.1) respectively, p < 0.001 for both). No significant relationship was seen between 25(OH)D (nmol/L) and change in BMI (p = 0.43), FFMI (p = 0.34), fat-mass index (p = 0.25), T-score hip (p = 0.19) or T-score lumbar spine (p = 0.21) over two years. Discussion: No associations between vitamin D status and BC or longitudinal changes in BC were found. However, the results demonstrate that vitamin D insufficiency and low BMD is more common in patients with COPD compared to controls. Our findings highlight the importance to routinely measure vitamin D status and BC in patients with COPD.