Delayed discharges - where people are stuck in hospital even though they are medically fit to leave - is fuelling a rise in overall death rates, research suggests.
Experts said a "crisis in the NHS" and problems in social care are at least partly to blame for rising death rates from 2015 onwards.
They 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.
A team from the universities of Liverpool, Oxford, Glasgow and York analysed data from August 2010 to March 2016 on delayed discharges and death rates across England.
In particular, they found rising problems 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 the extra deaths were down to delayed discharges.
They said: "For each additional acute patient delayed being discharged, we found an increase of 7.322 deaths.
"Our study provides evidence that a lower quality of performance of the NHS and adult social care as a result of austerity may be having an adverse impact on population health."
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.
Across England and Wales, there was a rise of 28,189 deaths in 2015 (up 5.6%), from 501,424 deaths in 2014 to 529,613 deaths in 2015.
The Office for National Statistics found there were 24,201 extra deaths in the 75 and over age group in 2015 - accounting for 86% of the total increase.
Dr Mark Green, from the University of Liverpool, who worked on the Journal of Epidemiology and Community Health 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%.
"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.
Dr Nick Scriven, president of the Society for Acute Medicine, said: "We, along with many other health professionals, have consistently raised the issue of delayed discharges over the past three years while the Government failed to acknowledge the scale of the crisis in social care and the record numbers of delayed discharges in our hospitals as a result."
Glen Garrod, vice president of the Association of Directors of Adult Social Services, said councils' adult social care budgets have been reduced significantly.
He added: "Although the findings appear to confirm views expressed elsewhere, it is important to note that other factors, aside from delayed discharge, may also have a bearing on the rise in mortality reported."
Caroline Abrahams, charity director at Age UK, said: "We already knew that being stuck in a hospital bed when you're medically fit to leave undermines your chances of a full recovery but this research raises the worrying question of whether in some instances it may shorten your life as well.
"That's why the Government must stand by its commitment to addressing the failings of our social care system, by investing in its future and publishing proposals that set out a long-term solution."
Saffron Cordery, director of policy and strategy at NHS Providers, said delayed transfers are bad for patients but it is uncertain how they contribute to death rates.
Public Health England said that despite the spike in 2015, the long-term trend is that death rates are falling.
Professor John Newton, director of health improvement at Public Health England, said: "The long-term trend for mortality rates in England has seen them steadily fall over time, but since 2011, although still falling, the rate of improvement seems to be less.
"One thing is clear, the reasons behind recent trends are complex with many potential causes, including but not limited to, the ageing population, global trends and influenza strains."
A Department of Health spokesman said: "Whilst the results of this research are limited, we are clear that no one should have to stay in a hospital bed longer than necessary.
"Both the NHS and local authorities have set ambitious targets to tackle this issue, supported by an additional £2bn of funding for social care from this Government. We are committed to consulting widely on how to improve the social care system and put it on a more secure financial footing for the future."
Copyright (c) Press Association Ltd. 2017, All Rights Reserved.