Government cuts to the pension credit have a "significant link" with a rise in death rates among older pensioners, Oxford University researchers have said.
The Government's austerity measures across England could have fuelled a rise in death rates among those aged 85 and over, their study found.
Professor David Stuckler, from the University of Oxford, said: "This study suggests that even seemingly small cuts to support for vulnerable older persons can have a devastating effect - possibly even costing them their lives."
Experts analysed Office for National Statistics (ONS) data on the death rates of pensioners across England between 2007 and 2013. They looked at corresponding figures on pension credits across 324 local authorities.
The numbers of people claiming pension credits was analysed alongside how much funding they received after cuts took effect.
Pension credits are intended to boost the finances of low income pensioners with a minimum income every week. At present, the guarantee part of pension credit tops up weekly income to £151.20 for a single person or £230.85 for couples.
Savings credit is an extra payment for people who saved some money towards their retirement but this has now been closed for new applicants as of last week.
Death rates among people aged 85 and over in England had been falling, the study found, but began to rise in 2011.
By 2013, death rates were 4% higher than in 2010 among men, while among women they were 6% higher.
During this period, average spending on the pension credit fell from £2,482 per claimant in 2011 to £2,349 in 2013.
Researchers found a significant link with rising death rates both for declines in pension credit spending per person and the number of people claiming the credit.
The study found that, between 2007 and 2013, each 1% decline in pension credit spending per eligible person was linked to a 0.86% rise in death rates.
Each reduction in the number of people able to get the benefit per 1,000 pensioners was also associated with an increase in death rates of 0.20%.
The modelling estimates that the average drop in pension credit spending per person in 2012 of 3% corresponds to a 1.4% rise in death rates.
And the decline in the number of people getting pension credit in 2012 translates to a rise of 2.7% in death rates.
Lead researcher Dr Rachel Loopstra, from the Department of Sociology at the University of Oxford, said: "Together, these changes are of a sufficient magnitude to explain almost 90% of the observed 4.6% rise in mortality of that year.
"Poorer older age adults are one of the most vulnerable groups in the population and a reduction of just a few pounds could make a considerable difference to disposable income.
"Declines of this magnitude can cause significant stress and anxiety to people of older ages, which could precipitate heart attack or stroke."
Researchers said increasing death rates could be fuelled by poorer nutrition, inadequate heating, damp housing and social isolation. Such increasing vulnerability also makes people more at risk from flu outbreaks.
"Both recent and proposed future changes to welfare spending fall heavily upon pensioners", Dr Loopstra said.
"The social care spending gap, exacerbated by population ageing and rising demand for services, has been projected to be £2.8 to £3.5 billion by 2019/20.
"Healthcare professionals have a crucial role in drawing attention to the consequences of these cuts and advocating publicly for policies that protect some of the most vulnerable individuals in society."
The authors said that while they could not show specific causes of death, financial hardship plays a role in increasing vulnerability. When the winter fuel payment was introduced in the 1990s, there was a significant drop in death rates, they said.
The study, published in the Journal of the Royal Society of Medicine, included experts from the University of Oxford, the London School of Hygiene and Tropical Medicine, the University of Glasgow and the University of Liverpool.
Professor Martin McKee, from the London School of Hygiene and Tropical Medicine, said: "The narrow focus on the state pension in policy debates has obscured how austerity measures may have negatively affected low-income, older pensioners."
A Department for Work and Pensions (DWP) spokesman said: "It's completely misleading to link these figures. The truth is that minimum income from pension credit has increased every year in line with earnings or more.
"And we have continued to protect pensioner incomes by safeguarding the triple lock and maintaining universal benefits such as winter fuel payments."