Homeless people aged between their 20s and 40s are physically comparable to people in their 70s and 80s.
A Trinity College study shows that those staying in hostels and rough sleeping have accelerated physical ageing, and have geriatric syndromes.
It found that 83 percent had mobility problems, while less than four in 10 could only walk for six minutes.
Researchers have recommended that a housing policy to respond to homeless people's physical needs is required.
Separately, the Peter McVerry Trust says the Covid-19 Pandemic helped to free up additional housing across the country last year.
The charity's annual report shows it helped over 7 thousand 800 people in 2020 to put a roof over their head, and almost half of its social housing tenancies went to rough sleepers.
It says the lockdowns freed up rental properties that would otherwise have been used by the business community to house overseas workers.