This definition has very strong theoretical and biological underpinnings, which may reflect an identifiable and shared bioinflammatory pathway between depression and frailty,8, 11 for example, C-reactive protein and interleukin-6 have been shown to be elevated in both people with frailty and people with depression;30, 31 and 2) one of the criteria of Fried frailty (exhaustion) is very common in people with depression.32 Here, IL6 is linked to depressive disorder.