“…The factors related to LIL can be viewed by individual level (demographics, health and psychological characteristics), interpersonal level (family relationship and marital status), and society level (culture, social environment and age friendliness). The factors include age, sex, race, education, socioeconomic status, marital status or widowhood, working status, having children or not, social relationship with friends and neighbors, social anxiety, Internet use, self-rated health, disability, resilience, previous depression, and built environment [ 10 , 21 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. In addition, social participation [ 44 ], activity engagement [ 45 ], bonding social capital [ 46 ], and religious belief or spirituality [ 47 , 48 ] may also be protective factors.…”