Jeremy Hunt’s claim that increasing hospital staffing at the weekends would help prevent thousands of deaths a year have been debunked in one of the largest studies to date.

Research led by Warwick University on the “weekend effect”, where death rates appear higher for patients admitted on a Saturday or Sunday, found little evidence the quality of care in hospitals was to blame.

After reviewing 68 studies spanning 640 million hospital admissions around the world, the researchers reaffirmed that patients admitted at weekends are sicker.

While patients admitted at weekends were on average 16 per cent more likely to die over the next month than those admitted on a Wednesday, the authors said staffing levels did not appear to account for this.

It follows a 2016 dispute between the government and junior doctors which led to the first ”all-out” strike, including A&E doctors, in NHS history.

In pictures: Junior doctors first all-out strike Show all 10 1 /10 In pictures: Junior doctors first all-out strike In pictures: Junior doctors first all-out strike Doctor in acute medicine, Melissa Haskins, holds up a 'I ain't afraid of no Hunt' sign whilst striking with other junior doctors outside her hospital, St Thomas' Hospital in London Getty Images In pictures: Junior doctors first all-out strike Accident and emergency junior doctor, Jennifer Hulse, holds a homemade placard outside St Thomas' Hospital as she strikes with colleagues in London Getty Images In pictures: Junior doctors first all-out strike Demonstrators and Junior doctors hold placards as they protest outside the Basingstoke and North Hampshire Hospital, in Basingstoke during a strike by junior doctors Getty Images In pictures: Junior doctors first all-out strike Demonstrators and Junior doctors hold placards as they protest outside the Basingstoke and North Hampshire Hospital, in Basingstoke during a strike by junior doctors Getty Images In pictures: Junior doctors first all-out strike A supporter displays a slogan on her bag during a junior doctors' strike outside St Thomas' Hospital in London Reuters In pictures: Junior doctors first all-out strike The picket line outside King's College Hospital in London PA In pictures: Junior doctors first all-out strike The picket line outside King's College Hospital in London, as thousands of junior doctors begun the first all-out strike in the history of the NHS after the Health Secretary said the Government would not be "blackmailed" into dropping its manifesto pledge for a seven-day health service PA In pictures: Junior doctors first all-out strike Junior doctors and supporters take part in a strike outside the Royal United Hospital in Bath Getty Images In pictures: Junior doctors first all-out strike Doctor in acute medicine, Melissa Haskins, holds up a 'I ain't afraid of no Hunt' sign whilst striking with other junior doctors outside her hospital, St Thomas' Hospital in London Getty Images In pictures: Junior doctors first all-out strike Dave Prentis, UNISON general secretary visits a British Medical Association picket line at Royal Sussex County Hospital in Brighton, to show support for striking junior doctors on the second day of the union's annual health conference PA

The row was sparked after the then-health secretary Jeremy Hunt used a 2015 study of the NHS weekend effect to justify forcing through a contract, which doctors leaders called unsafe, in a bid to have more staff working at weekends.

However, leaked emails made clear the Department of Health’s own advisers warned calling the deaths preventable would be “rash and misleading” and questioned whether more staff would help.

But the latest study, published in the journal BMJ Open, says the weekend effect is not a uniquely UK phenomenon and evidence that it is to do with low-quality care is limited.

“We have some evidence that the higher mortality associated with weekend admissions is because weekend patients are sicker when they are admitted into the hospital,” said Dr Yen-Fu Chen, lead author of the study.

“But evidence regarding whether these patients receive inferior care following admission compared with those admitted on weekdays is sparse and somewhat conflicting.”

A third of the studies in the review came from the UK, a third from the US and the remainder from around the world.

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The review found that previous studies had not done enough to record how seriously ill patients were at the point they were admitted – where this had been recorded, the weekend effect was reduced.

It also found the weekend effect was most pronounced in patients who were admitted for planned (elective) procedures at the weekend, but was virtually absent for maternity services.

Professor Julian Bion, another of the authors from the University of Birmingham, said: “It is likely that elective admissions, usually for surgical operations, at weekends are those with more urgent problems and more complicated issues, which will contribute to the higher mortality.

“These factors seem to explain much of the higher mortality risk among weekend admissions.”

He said the search for the cause of the weekend effect needed to include “the whole patient pathway”, particularly care outside of hospital before and after they fell ill or were discharged.

“The bottom line is, do not be deterred or delayed by the apparent ‘weekend effect’ if you need health care at weekends.”

The Department of Health and Social Care said it was continuing to pursue negotiations of senior consultants contracts, which currently allow them to opt out of weekend work though, in practice, few do.