ABSTRACT
The World Health Organization (WHO) emphasized the importance of functional ability throughout life to achieve a state of healthy longevity. Loneliness and social isolation, two important determinants of healthy aging, describe two different socially vulnerable states. Generally speaking, loneliness is an unpleasant subjective feeling of loss of an individual’s social network and social isolation is the discontinuation of actual relationships with society members, groups, and communities. In theory, both conditions substantially aggravate declines in physical function, cognitive function, and mental health; however, evidence supporting causal relationships is scarce. International cross-sectional and longitudinal studies have confirmed that loneliness and social isolation are associated with frailty, sarcopenia, dementia, cognitive impairment, and depression in a complicated way. Although there are no well-designed intervention trials to confirm the causal relationships of the abovementioned complex associations, it is generally agreed that nonpharmacological interventions aiming to reduce loneliness and social isolation have great potential benefits for physical, cognitive, mental, and social domains in the aging process. Hence, more studies adopting biopsychosocial approaches are needed to examine the abovementioned complicated associations, thereby facilitating the development of effective intervention programs.
