GDF15 and pneumonia: Three baseline serum protein measurements were associated with pneumonia risk independent of measured clinical factors: growth differentiation factor 15 (SHR 1.32; CI 1.02–1.69), C-reactive protein (SHR 1.16, CI 1.06–1.27) and matrix metallopeptidase 8 (SHR 1.14, CI 1.01–1.30).