Table 1.

Health-relevant correlates and consequences of loneliness by age group.

outcome	later childhood and early adolescence (6–12 years)	adolescence (13–17 years)	early and mid-adulthood (18–49 years)	later adulthood (50+ years)
mental health	→ depressive symptoms [26–28]	→ depressive symptoms [29–32]	→ depressive symptoms [33–35]; depression, pain and fatigue [36]	→ depressive symptoms [37–39]; depression, pain and fatigue [36]
sleep	→ poor sleep quality [27]	→ poor sleep quality [40]; → shorter sleep duration [41]	poor sleep quality [40,42,43]	→ poor sleep quality [44,45]
executive control	impaired executive control [46]	→ impaired control over eating behaviour in overweight adolescents [47]	poorer attention regulation [48,49]; impaired control over eating behaviour [49]	impaired optimization of positive emotions [50]
self-reported health	→ poorer general health [27]; more somatic symptoms [28]	→ poorer general health [32,51]; see also [28,34]	→ poorer general health [33,34]	→ poorer general health [52,53]
healthcare utilization		→ increased frequency of doctor visits [32]	increased use of hospital emergency department [54]	increased likelihood of nursing home admission [55]
cognitive functioning				impaired cognitive abilities [56,57]; → cognitive decline and dementia [58–61]
immune functioning			impaired cellular immunity [62–65]; impaired humoral immunity [42]
neuroendocrine functioning			→ increased cortisol response to awakening [42,66]	→ increased cortisol response to awakening [67,68]
inflammation			increased pro-inflammatory cytokine response to acute stress [69,70]	pro-inflammatory gene expression [71–73]
mortality				→ mortality [74–79]

→ refers to prospective effects of loneliness.