1.2. Loneliness in Older Adults
The definition of loneliness is the gap between real and wished for social relationships [20,21]. Similar to subjective age, loneliness is a subjective concept and not an objective social manifestation [20]. Although loneliness can be connected with objective aspects of the social network including the number and frequency of actual social contacts, it is not synonymous with these aspects and it still represents the qualitative elements of relationships [22].
With a few exceptions, the majority of past research has emphasized the role of loneliness as a strong predictor of morbidity and mortality [23,24]. A considerable body of research has pointed out that a high level of loneliness is a major risk factor for cardiovascular diseases [25], disability [26], poor sleep hygiene [27], impaired cognition [28], and impaired physical functioning [22]. These negative effects of loneliness might explain the possible association between feelings of loneliness and subjective age, and in contrast, the negative correlation between size of friendship network and self-perception of age (for example, the finding that women who felt themselves younger than their actual age had larger friendship networks [29]. Moreover, a recent study suggested a plausible causal model of loneliness leading to morbidity and mortality, and found evidence of mediation by subjective health, depressive symptoms, and functional limitations [30].
Although objective indicators of social relationships also predict health and well-being [31,32], these are generally thought to exert a somewhat smaller effect in comparison to loneliness. However, there is general consent that loneliness increases with age among older adults [33]. This is not surprising given the many objective losses that take place in advanced age [33]. Objective losses include, for example, retirement because it is often associated with the narrowing of one’s social network or the death of a spouse, siblings, and close friends, which also result in reduced social contact [34,35].