TNF and insomnia: Given that inflammation is known to be one of the pathophysiological bases of frailty (7), the association between sleep quality and frailty stages could also be explained on the basis that sleep disorders, such as insomnia and long sleep duration, favor changes in inflammation levels involving increased C-reactive protein, interleukin-6 and tumor necrosis factor (TNF-α) (32, 35, 36).