An epidemiologist at the University College London(UCL) named Daisy Fancourt conducted a study on the effects of enforced isolation and other pandemic related changes on the British population. Research has always proven that self isolation can cause mental health disorders as well as other physical complications. Fancourt and her colleagues focused more on how social factors like isolation affect mental and physical health. They recruited more than 70,000 participants who shared their experiences via weekly online surveys and telephone interviews. Prior to covid-19, millions of people experienced social isolation which was usually willingly. Fancourt explained her findings when she stated "We are seeing a really growing body of evidence that's showing how isolation and loneliness are linked in with incidence of different types of diseases [and] with premature mortality." Social isolation is also known to increase risks of cognitive decline and dementia, along with depression anxiety.
Source 1: https://www.the-scientist.com/features/how-social-isolation-affects-the-brain-67701
Source 2: https://journals.sagepub.com/doi/full/10.1177/0020764020922269