Loneliness, in turn, is a risk factor for various physiological and health outcomes. These include low socioeconomic status, poor marital quality, infrequent contact with friends and family, few social roles, lack of participation in voluntary organizations, physical health symptoms, and physical limitations ( Hawkley et al., 2008 Savikko, Routasalo, Tilvis, Strandberg, & Pitkala, 2005). People can feel lonely in a marriage or in a crowd ( Cacioppo et al., 2000 Tornstam, 1992), but certain situational factors heighten the risk for increased loneliness. Twin studies reveal that loneliness is temporally stable and heritable, with approximately equal parts attributable to heritable and non-shared environmental factors in adulthood ( Boomsma, Willemsen, Dolan, Hawkley, & Cacioppo, 2005 Boomsma, Cacioppo, Muthen, Asparouhov, & Clark, 2007). Millions of people suffer daily from loneliness ( Rubenstein & Shaver, 1982 Steffick, 2000), a debilitating psychological condition characterized by a deep sense of emptiness, worthlessness, lack of control, and personal threat ( Booth, 2000 Cacioppo & Patrick, 2008 Weiss, 1973). The word “solitude” expresses the glory of being alone, whereas the word “loneliness” expresses the pain of feeling alone ( Tillich, 1959). Loneliness and the feeling of being unwanted is the most terrible poverty. The importance of distinguishing between loneliness and depressive symptoms and the implications for loneliness and depressive symptomatology in older adults are discussed. Cross-lag analyses indicated that loneliness predicted subsequent changes in depressive symptomatology but not vice versa, and that this temporal association was not attributable to demographic variables, objective social isolation, dispositional negativity, stress, or social support.
Variations on this model evaluated the possible effects of gender, ethnicity, education, physical functioning, medications, social network size, neuroticism, stressful life events, perceived stress, and social support on the observed associations between loneliness and depressive symptoms. Cross-lagged panel models were used in which the criterion variables were loneliness and depressive symptoms considered simultaneously. We present evidence from a five year longitudinal study for the prospective associations between loneliness and depressive symptoms in a population-based, ethnically diverse sample of 229 men and women who were 50-68 years old at study onset.