The study looked at 137 NHS Trusts and found that mortality rates were lower in hospitals where nurses had fewer than six patients, compared with those attempting to cope with more than 10.
It comes at a time when there’s growing concern about short staffing across the health service.
The research looked at links between the number of nurses, doctors and healthcare assistants and patient deaths.
Ministers have pledged to introduce a new type of nursing worker, with less training that a registered nurse, to help with staff shortages.
However, the report found that providing more healthcare assistants instead of nurses did not prevent the rise in patient mortality.
Anne Marie Rafferty, Professor of Nursing Policy at King’s College, London, told The Daily Telegraph: “This is the first study to shed light on the policy of shifting the safe staffing policy decision from nursing to that of the clinical team. It flags the need for caution and the dangers of simply substituting healthcare support staff for qualified nursing staff.”
Research author Dr Jane Ball, from Southampton University, said: “When determining the safety of staffing on hospital wards, the level of registered nurse staffing is crucial; hospitals with higher levels of healthcare support workers have higher mortality rates.”
“Patients should not be asked to pay the price of receiving care from a less skilled and less educated member of staff, just to make up for the failure of the system to ensure enough registered nurses,” she added.