[…] Doctors and policymakers in the rich world are increasingly worried about loneliness. Campaigns to reduce it have been launched in Britain, Denmark and Australia. In Japan the government has surveyed hikikomori, or “people who shut themselves in their homes”. Last year Vivek Murthy, a former surgeon-general of the United States, called loneliness an epidemic, likening its impact on health to obesity or smoking 15 cigarettes per day. In January Theresa May, the British prime minister, appointed a minister for loneliness.