This is the second highest cause of absence behind home and family issues (20%), and is even ahead of acute medical conditions such as heart attacks or cancer.
The problem of stress seems is worse in the public sector, with 27% of public sector employers citing this as their main cause of absence compared with 13% in the private sector. Following a year of budget cuts and redundancies, it indicates that these pressures have had an impact on the health of the workforce.
As a result of high absence levels through stress, almost one in five employers (19%) stated that stress or other mental health issues are the biggest health-related problem for their business. This percentage rises to over a quarter (27%) for businesses with over 100 staff.
The figures are particularly timely in light of Stress Awareness Day today (2 November), which aims to highlight the problem of stress in the workplace.
Katharine Moxham, spokeswoman for GRiD, said: "Stress is often overlooked as a cause of long-term absence from work, compared to acute medical conditions such as heart attack or cancer. These figures prove just how big a problem absence through stress is for employers, and provide a timely reminder for businesses to take action over what is often a preventable condition.
"In times of increased economic pressure it is important for employers to consider firstly the wellbeing of their employees and what wider implications are suggested by high levels of stress or other mental illness, and secondly what provisions they have in place to ensure both the employee and the employer are adequately protected in case of long-term absence.
Many employers in the private sector have a group income protection (GIP) scheme in place as part of their overall absence management strategy. This can provide peace of mind and security to all involved.
"GIP provides a continuing income for employees if illness or injury prevents them from working for a prolonged period of time. It can also replace lost income where an employee has to take a part-time or lower-paid position because of illness or injury. As well as the financial advantages of having insured their liability to continue salary in the event of long-term disability, given that vocational rehabilitation is a primary feature of most GIP policies, an employer with a current generation GIP policy in place will be well-equipped to manage an employee's absence and provide the support they need to get back to work.
"As welfare reform moves forward, any business that has already embraced the value of integrated health, wellbeing and absence programmes will feel vindicated; any business that has not already understood how crucial this is will come to do so."
A separate report from the CIPD last month found stress had become the biggest cause of long-term absence for the first time in the 12 years it had been measuring absenteeism.
Jill Miller, CIPD adviser, said: "Our research shows that stress is a problem that is increasing in frequency. However, rather than employers simply consigning themselves to this issue, there are many things they can do to help ease the pressure on employees and help them to strike the appropriate balance between their private and working lives.
"Effective people management and leadership is vital, line managers are well-placed to spot early warning signs of stress and put initiatives in place to help employees through difficult periods. It is important for managers to build a trusted and open relationship with employees, having good quality conversations and communicating organisational change clearly."