Loneliness can afflict anyone, whether young or old, rich or poor, highly-educated or illiterate, healthy or infirm. Because children are almost invariably reared in a network of intimate relationships that, if not a natural or adopted family, has some other social context (usually institutional) in the first three or four years, the individual is imprinted with the norm of being accompanied. Someone – whether parents, siblings, age cohorts, friends, relatives, social workers – is in daily contact with the child. This position of security may change gradually, for instance, if childhood companions grow away from each other, or suddenly, perhaps by a change in location or situation or by a death.
Health studies say that loneliness can disrupt sleep, increase stress, weaken the immune system, accelerate cognitive decline and frailty and is linked to heart disease and depression. They argue that loneliness has such a significant effect on mortality rates that it could be considered a public health threat more harmful than obesity and akin to smoking, high blood pressure, high cholesterol, obesity and lack of physical exercise.
People who are physically isolated, such as those who work at home or in remote areas, are hospitalized or otherwise infirm, are often subject to loneliness. Equally painful is the subjective loneliness experienced by a shy or sensitive person, or by one who is, for whatever reason, alienated from society. People who are isolated but healthy are twice as likely to die over the period of a decade or so as others with the same health. Men are at more danger than women.
Cigna, a U.S. medical insurer, based on an online survey with 20,000 adult respondents, reported in 2018 that most Americans are lonely. Surprisingly, the highest rates of loneliness were not found among the elderly, but in Generation Z (ages 18 to 22) and millennials (ages 20 to 35): nearly 50 percent of respondents said they sometimes or always feel alone or left out; just 53 percent have meaningful in-person social interactions on a daily basis; 27 percent rarely or never feel as though there are people who really understand them.