Researchers from the University of York joined teams from Liverpool, Oxford and Glasgow in analysing data from August 2010 to March 2016 on delayed discharges across England.
They said a “crisis in the NHS” and problems in social care are at least partly to blame for rising death rates from 2015 onwards.
Researchers believe delayed discharges - which are often caused by an inability to arrange adequate social care in the community for people leaving hospital - could be preventing other, sick people from being admitted to hospital for the care they need.
Meanwhile, those stuck in hospital may experience more stress and anxiety, and could receive less-good care as time goes on.
The research comes just days after The Yorkshire Post exclusively revealed that the care crisis most often associated with the winter stretched throughout the year, with some patients in Yorkshire stuck in hospital for up to five months despite being declared fit to go home.
The research out today showed rising problems in delayed discharges and death rates from 2014/15 onwards, with a high concentration of deaths among older, frail people.
For example, between July 2014 and June 2015, there were an extra 39,074 deaths in England and Wales compared with the same period the previous year.
“While mortality rates fluctuate year on year, this was the largest rise for nearly 50 years and the higher rate of mortality has been maintained throughout 2016 and into 2017,” the authors wrote in the Journal of Epidemiology and Community Health.
They added: “The increase in mortality rates has occurred during a crisis in the National Health Service (NHS). The number of NHS trusts with budget deficits has increased sharply since 2014/2015, as did waiting periods for elective surgery in 2015.
“Issues within the NHS are being compounded by problems with the provision of adult social care to support individuals leaving NHS care and pressures of increased demand.”
The authors estimated that up to a fifth of excess deaths were down to delayed discharges.
Previously, health officials have suggested flu was to blame for taking the lives of a significant number of people aged 75 and over in 2015 - 24,201 extra than in 2014.
Dr Mark Green, from the University of Liverpool, who worked on the study, said flu was a factor in 2015 but cannot account for the entire increase in deaths.
He said: “It also does not explain that mortality rates were higher in warmer months compared to previous years - ie when flu does not operate.”
He added: “Since 2014, the number of patients admitted for acute conditions who were delayed being discharged from hospital has almost increased by 50 per cent.
“This creates blockages in the NHS where beds are not available for new patients, and since these individuals are being admitted for acute and often pressing issues any delay to accessing services can be deadly.
“It is clear that increased funding to both the NHS and adult social care to minimise issues with discharged patients would benefit the population widely.”
NHS England declined to comment on the study.
Campaigners said the Government must address the failings of the social care system.
Caroline Abrahams, charity director at Age UK, said the research raises “the worrying question” of whether in some instances, a stay in hospital it “may shorten your life”, and called on the Government to invest in the social care system.
Dr Nick Scriven, president of the Society for Acute Medicine, said it was “essential to patient safety” that the right support and infrastructure is in place; and Glen Garrod, vice president of the Association of Directors of Adult Social Services, said the report “shines a light on the important debate” about what is happening to people who need support at a time when councils’ social care budgets have reduced.