Almost 200,000 people over the age of 75 have left hospital without proper support, increasing the likelihood of being readmitted, according to a new report.
The Royal Voluntary Service said better support could save the NHS in England more than £40 million and prevent thousands of readmissions.
Older people are vulnerable and frail during a stay in hospital, but 13% of over 75s are readmitted for treatment within three months of being discharged, said the report.
Almost one in seven feels anxious at the prospect of returning home, especially those who live alone.
David McCullough, chief executive of the Royal Voluntary Service said: "The population is living longer, an achievement which should be celebrated - yet it is presenting a challenge for the very organisation that has helped people live longer lives.
"With local authority and hospital trusts facing budget cuts, we believe greater volunteer support through home-from-hospital schemes can improve the quality of older people's lives long after a hospital stay and save the NHS millions of pounds.
"Placing a caring volunteer at the centre of an older person's recovery plan dramatically improves their experience, their confidence and their well-being, and helps them continue to live independent fulfilling lives. It also drives important efficiencies in hospitals enabling swift, well-managed discharge from wards.
"A strong warning sign identified in the report is the link between early discharge and readmission."
David Buck of The King's Fund, which helped with the research, said: "Well-targeted home-from-hospital support schemes could reduce the need for inappropriate and avoidable hospital readmission and other forms of care.
"Whilst as a consequence this may save the NHS significant sums, their ultimate objective is better health and wellbeing of elderly people, for which there is good evidence."
The study was based on a survey of more than 400 people aged 75 and over.
The report marks the launch of the Royal Voluntary Service's Let's End Going Home Alone campaign, which involves the charity working in partnership with communities, local authorities and NHS Trusts to provide more volunteers in hospitals and support vulnerable older people in their homes following discharge from hospital.
Minister for Care and Support Norman Lamb said: "I am delighted to give my support to this campaign - it's absolutely right older people are given the support they need when they leave hospital and volunteers have an essential role to play.
"Our £5.3 billion Better Care Fund will mean 163,000 fewer A&E visits next year and more people helped to live independently at home for longer after leaving hospital, giving older people the dignity they deserve."
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