The Royal College of Nursing (RCN) said there was a clear link between failing care and the poor workforce numbers.
A report by the RCN said a recent survey suggested that two-fifths of nurses in the UK reported that care was compromised at least once a week as a result of staffing shortages.
It found that "avoidable complications", such as deep vein thrombosis (DVT), urinary tract infections (UTIs) and pressure ulcers, were avoidable only if nursing care was delivered effectively.
This relies on having sufficient nurses with the right skills in place, according to the guidance on safe nurse staffing levels in the UK report.
The report comes as the NHS in Scotland aims to reduce its workforce by about 3,800 as part of efforts to tackle financial cutbacks.
But unions have warned that using staff turnover to reduce numbers, but not replacing those who leave, can mean key workers are lost in the wrong places.
The RCN said Scotland was the only part of the UK that had nationally agreed workforce and workload planning "tools" for the nursing workforce, which were designed to ensure health boards employed the right number of nurses and unregistered nursing staff with the right skills in the right places.
However, the RCN said health boards were disregarding the tools and were relying on staff turnover and other "short-sighted" measures to reduce nursing and other staff in an attempt to balance their books.
RCN Scotland director Theresa Fyffe said the report made it clear that the right staffing levels were crucial in ensuring safe patient care.
Health Secretary Nicola Sturgeon said yesterday: "Health boards are using the workforce planning tools available to provide high-quality and efficient services."