“…The underlying causal mechanisms of the effects of loneliness and social isolation on mortality are not yet clear. Research has focused on dysregulation of the hypothalamic-pituitary-adrenal axis as a putative mediator in the association between loneliness and social isolation and higher mortality, since both high cortisol levels (Aubert, Folly, Mancinetti, Hayoz, & Donze, 2016;Hammer et al, 2016;Zurfluh et al, 2018) and low cortisol levels (Maripuu, Wikgren, Karling, Adolfsson, & Norrback, 2016) are associated with higher mortality. In older adults, loneliness has been found to be associated with a higher cortisol awakening response (Adam, Hawkley, & Kudielka, 2006;Steptoe, Owen, Kunz-Ebrecht, & Brydon, 2004) but also with diminished cortisol output (Schutter et al, 2017).…”