Study Links Nurse Understaffing to Higher Risk of Death, Readmissions

Recommendations do not go far enough in calling for policy action, experts say

Published on Mar. 2, 2026

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A retrospective cohort study from Japan suggested that understaffing of hospital nurses was linked to worse patient outcomes, especially during day shifts. Patients exposed to nurse understaffing over a 24-hour period and during day shifts had higher risks of in-hospital mortality and readmission.

Why it matters

These findings were consistent with prior studies from England and the U.S., among others, highlighting the widespread issue of nurse understaffing and its detrimental impact on patient care and outcomes. The study authors argue that hospital leaders and policymakers need to take corrective action to address this problem.

The details

The study analyzed data from more than 77,000 hospital admissions across 82 acute care hospital wards in Japan. Patients exposed to nurse understaffing over a 24-hour period and during day shifts had a higher risk of in-hospital mortality and 30-day readmission compared to those with adequate staffing. Understaffing during evening and night shifts was not linked to these negative outcomes, but was associated with increased length of stay.

  • The study period was from April 2019 through March 2020.

The players

Noriko Morioka

PhD, of the National Institute of Public Health in Wako, and co-author of the study.

Karen B. Lasater

PhD, RN, of the University of Pennsylvania in Philadelphia, and co-author of the accompanying commentary.

Linda H. Aiken

PhD, RN, of the University of Pennsylvania in Philadelphia, and co-author of the accompanying commentary.

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What they’re saying

“The underlying mechanism is that low nurse staffing levels have been associated with missed nursing care, which in turn may lead to adverse patient outcomes ... as well as inadequate discharge preparation resulting in higher rates of readmission.”

— Noriko Morioka, PhD, of the National Institute of Public Health in Wako, and co-author of the study (JAMA Network Open)

“It is discouraging, although typical, that more than 15 years passed between the 2 studies in Japan on the same topic without serious policy attention to persistent hospital nurse understaffing associated with potentially preventable deaths and unrealized cost savings due to higher than necessary length of stay and readmissions.”

— Karen B. Lasater, PhD, RN, of the University of Pennsylvania in Philadelphia, and co-author of the accompanying commentary (JAMA Network Open)

“Hopefully, hospital leaders and policymakers in Japan will recognize the value of the robust evidence compiled [in this study] and consider taking corrective action before another 15 years of inattention pass to the detriment of hospitalized patients and their nurses.”

— Linda H. Aiken, PhD, RN, of the University of Pennsylvania in Philadelphia, and co-author of the accompanying commentary (JAMA Network Open)

What’s next

The authors argue that the study's recommendations do not go far enough in calling for policy action, and urge Japan to look to examples of safe nurse staffing standards implemented in parts of Australia, Canada, California, and Oregon.

The takeaway

This study adds to the growing body of evidence linking nurse understaffing to worse patient outcomes, including higher mortality and readmission rates. Hospital leaders and policymakers need to take concrete steps to address this issue and implement safe staffing standards to protect both patients and nurses.