Workers took a total of 17.7 million days of sick leave between December 2017 and November 2018.
Of these, almost a quarter or 4.2 million were taken due to stress, anxiety, depression or other psychiatric illnesses.
That was more than the next two most common reasons combined, which included musculoskeletal conditions and the common cold.
The Sheffield Health and Social Care Foundation Trust had the highest proportion of lost days to depression and other psychiatric conditions, with 38 per cent accounted for by those conditions.
The findings have prompted the UK’s largest healthcare workers’ union, Unison, to call on the government to invest more money into NHS services.
The union’s deputy head of health, Helga Pile, said that having to contend with intolerable work pressure, bullying, and intimidation and violence from patients were just some of the reasons so many NHS workers struggled with mental health issues.
“Chronic staff shortages mean NHS employees are routinely being asked to do more with fewer resources as they desperately try to keep the service afloat,” she added. “The government urgently needs to invest in the NHS to cut staff shortages and reduce burnout, and workers suffering anxiety, depression and stress must get rapid access to mental health support services.”
Emma Mamo, head of workplace wellbeing at the charity, said it was important for employers to support struggling employees and tackle work-related causes of mental health problems, particularly in the NHS.
“We know there can be particular barriers for healthcare staff when disclosing a mental health problem to their employer, such as fears about being deemed unfit to practise,” she said. “Those of us with mental health problems can and do make a valuable contribution to the workplace, it just means some of us might need extra support from time to time.
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“Healthcare staff can make a real difference to the experiences of people accessing NHS services.”
In response to the findings, a spokesperson for NHS England said it is committed to taking care of its staff and offers “support, good occupational health, flexible working and a range of other measures”.
They added: “Staff are the lifeblood of the NHS, and we are already offering the most comprehensive national mental health support offer to doctors of any health system in the world, and are committed to doing similarly with other staff groups.”