Loneliness among community-dwelling older adults across biological, clinical and psychosocial domains before and during the COVID-19 pandemic: a systematic review.

Background: Loneliness is a subjective and distressing experience resulting from a discrepancy between desired and actual social relationships and represents an important public health concern among community-dwelling older adults. Although it can occur throughout the life course, older adults are particularly vulnerable because of age-related conditions such as multimorbidity, mobility limitations, sensory impairments, widowhood, and retirement. These factors highlight the need to understand loneliness as a multifactorial phenomenon requiring a multidimensional perspective considering biological, clinical, and psychosocial determinants and consequences. Objectives: This systematic literature review aims to investigate the extent to which the available literature on loneliness in older age adopts a multidisciplinary approach. Research design and methods: Multiple databases were searched and papers in biological, clinical and socio-psychological areas were selected according to predefined inclusion criteria and the PRISMA guidelines. Study characteristics (author, year of publication, methodology, and sample size) and contents (keywords, loneliness as primary or secondary outcome, multidisciplinary) were analysed. Results: One hundred thirty-one articles were selected: 22 biological; 51 clinical and 58 socio-psychological. Eighty-nine studies adopted quantitative methods, mostly concentrated in the biological area, while qualitative and mixed-method approaches are more common in the other two areas. In biological papers, loneliness is treated as an etiopathological factor or pathological condition, thus underestimating or denying its social significance. Clinical papers often associate loneliness with depression and socio-psychological ones do not investigate loneliness biological and clinical implications. Discussion and conclusion: Although the COVID-19 was associated with a growing number of multidisciplinary studies, research on loneliness among older adults remains largely fragmented across disciplinary boundaries. Strengthening collaboration across biological, clinical, and psychosocial domains could contribute to a more comprehensive understanding of loneliness and support the development of more effective prevention and intervention strategies.