For example, in 2013, I reported on research finding that loneliness can impair health by raising levels of stress hormones and inflammation, which in turn, can increase the risk of heart disease, arthritis, Type 2 diabetes, dementia, and even suicide attempts.
But people can be socially isolated and not feel lonely; they simply prefer a more hermetic existence. Likewise, people can feel lonely even when surrounded by lots of people, especially if the relationships are not emotionally rewarding.
Perhaps equally surprising is the finding that older adults are not necessarily the loneliest among us. Although most studies of the effects of loneliness have looked only at older people, Dr Holt-Lunstad, who with colleagues, has analysed 70 studies encompassing 3.4 million people, said that the prevalence of loneliness peaks in adolescents and young adults, then again in the oldest old.
Read more at https://www.channelnewsasia.com/news/health/how-loneliness-affects-our-health-9492106
You may want to read Loneliness is as bad for health as smoking 15 a day