Half a million older people spend every day alone, figures have revealed.
The research shows 500,000 over the age of 60 usually go at least five or six days a week without seeing or speaking to anyone at all, according to Age UK.
The charity has launched a report 'No one should have no one: working to end loneliness amongst older people' to tackle loneliness in older people.
At least 1.2 million older people in England are chronically lonely, having experienced loneliness for many years, the report warns.
This is leading to an increased demand on health services, partly because people are more likely to develop health conditions such as heart problems, depression and dementia, it says.
It comes as helpline for older people The Silver Line reported that it received more than one call every minute, every day throughout the Christmas period.
Age UK have carried out a pilot programme which has showed "great promise" in helping to reduce loneliness.
Age UK staff and volunteers carried out a "guided conversation" with those experiencing loneliness to discover people's life circumstances, interests and ambitions as well as the kind of support that might help them to feel less lonely.
Some older people were matched with volunteer friends, introduced to social groups, learned new IT skills to help them stay in touch with friends and family, or were given practical support to help them get back on their feet after a fall or illness.
Being given help to claim benefits such as Attendance Allowance and Pension Credit also helped people feel better and more able to connect with their communities.
"It's not so much about being alone," said one participant, "It's about being lonely, sometimes even when people are visiting…. I'm feeling happier and less nervous now."
"Getting older people to engage and acknowledge their loneliness was challenging at times, but taking an individual approach to each client really pays off." said Age UK's Volunteering and Community Activities Manager.
Age UK is calling on all MPs to put the issue of loneliness in later life firmly on the Government's agenda.
Chairs of three influential House of Commons committees have written to Theresa May to say that political consensus was needed to find a long-term solution to the "pressing" social care challenges facing the country.