° Depression associated with social isolation (f), physical inactivity (m) and lower BMI (m). ° Inflammatory marker high-sensitivity C-reactive protein (hs-CRP) not associated with depression or social isolation. °Hs-CRP levels higher for people with depression and social isolation (m). ° Inflammatory marker interleukin-6 (IL-6) associated with social isolation (m). ° IL-6 levels higher for people with depression and social isolation (m). Here, CRP is linked to major depressive disorder.