Mental ill health has become the second largest cause of sick leave in the UK, a new study claims.
Workplace problems relating from stress, anxiety and depression come second now only to muscle-related problems including bad backs.
The study, conducted by the Chartered Institute of Personnel and Development (CIPD), revealed that mental ill health results in employees taking up to three weeks off work at any one time.
Ben Willmott, employee relations advisor at the CIPD, said there is still a stigma attached to mental illness that both employees and employers need to tackle.
"I think what we're seeing in regards to mental ill health is quite often individuals will go off with short-term illnesses to start, so things like colds and flu, then suddenly they will go off with a long period of depression, stress or anxiety," he told the Today programme.
"So I think what we're seeing is maybe a reluctance for people to hold their hand up and say: 'I am suffering from a mental ill health condition and I need help'."
He added that in 1995 about 25 per cent of incapacity benefit claimants were suffering from some sort of mental illness but this has now risen to about 40 per cent.
Employers, he said, must ensure that line managers and HR practitioners must be able to spot the warning signs of mental ill health at work.
"Are there changes in an individual's performance? Obviously absence, mood changes, these sorts of thing can indicate that someone is suffering from excessive pressure or suffering from a mental health problem," Mr Willmott said.
Paul Farmer of mental health charity Mind added that employers must do more to remove the stigma of mental illness.
He told BBC's Radio Five Live that it makes business sense for employers to support workers with mental ill health.
"I think what this report suggests is that employers aren't getting it right every time but that it's everybody's business to take mental health seriously," he said.