Social isolation was equivalent to smoking 15 cigarettes or drinking six units of alcohol a day, according to the research.
The report showed 18 per cent of people under 30 had felt lonely at least some of the time in the previous four weeks.
Among those 30 to 64 years, 16 per cent had felt lonely. Among people aged 65 and over, the figure was just 11 per cent. Adults who had migrated to New Zealand in the past four years were also more likely to suffer loneliness.
Victoria University migration specialist Professor Colleen Ward said when people moved to a new country they rarely had support networks in place, and so had to start from scratch.
"They're starting without the advantages of people who have been situated for quite a while and have their supports in place," Prof Ward said.
Language skills were also a major factor, as a lack of English often prevented new migrants from establishing new relationships, Prof Ward said.
Adolescent psychology specialist, Associate Professor Paul Jose said adolescents reported high levels of loneliness due to the intense motivation to spend time with others.
"There's a very strong motive to have friends ... If somebody experiences difficulty with that, the loneliness can be quite intense," Dr Jose said.
While social media played a role in loneliness with youth, it was not to blame, Dr Jose said.