The U.S. has an all-time record number of actively licensed nurses — 5.6 million — but hospitals are struggling to recruit and retain enough. To discover missed opportunities, researchers surveyed 7,887 nurses who recently exited the healthcare industry.

Each nurse was asked to list the contributing factors for their decision.

Planned retirement was the leading factor, with nearly 2 in 5 nurses selecting that factor, but burnout, exhaustion, staffing shortages and family obligations were also top reasons.

About 60% of retired nurses indicated a planned retirement, suggesting that about 40% of retirements were unplanned, the researchers said.