Every two minutes, a worker in the UK becomes ill through stress at work, leading to 11.3 million lost work days a year.

Stress isn't the top cause of work days lost to long-term sickness, however - that dubious honour goes to back pain, responsible for more than 15 million sick days annually. And then there are the bugs that do the rounds - the average Brit gets between two and five colds a year, after all, and flu can wipe people out for a week or two.

While the average sickness absence for UK workers is five days each per year, according to the TUC, overall, around 170 million work days are lost every 12 months because people are too poorly to go in. 23 million of these are down to work-related ill health, and four million are as a result of injuries suffered at work.

So what's going on, and what does it mean to 'call in sick' these days?

COMMON COMPLAINTS Dr John Chisholm, health and work lead for the Royal College of GPs, confirms that although many medical problems can cause sickness absence, a significant majority of sick leave requests are either because of musculoskeletal problems (injury or disorders of the joints or other tissues in the limbs or back) or are related to mental health, such as anxiety, depression and stress.

"The stress that's adversely affecting mental health may itself be related to work," he points out.

DULY NOTED Where once doctors dished out 'sick notes', these days employees are required to provide employers with a 'fit note' if they're off sick for more than seven days in a row, including non-working days, These can be issued by hospital doctors or GPs, and will state that the employee is either 'not fit for work', or 'may be fit for work' - with the assumption that workers and their employers should discuss any suitable changes that may need to be made, such as altering their hours or duties, in order to support this. I f there's no agreement on these changes, the employee should be treated as 'not fit for work'.

If somebody's off for less than seven days, their employer may ask them to fill in a self-certification form when they return, to confirm they've been off.

JUDGEMENT CALL Anyone can ask for a fit note, but Dr Chisholm stresses that while a GP's role as their patients' advocate remains paramount, there's been a shift in attitudes about whether it's best for people to take time off sick.

"There's now much greater awareness that patients' best interests are served, and their health and wellbeing protected by encouraging them to remain in, or return to, work," he says.

There's strong evidence that working has positive benefits for both physical and mental health and wellbeing, and of the damage caused by prolonged sickness absence.

"Most GPs are only too aware that the longer someone's off sick, the harder it is to get back to work. Worklessness comes at great personal, financial and social cost," says Chisholm. "So GPs will make a judgement as to what's in their patient's best interest."

This could include suggesting changes to their work patterns and duties that could enable somebody to more comfortably remain at work.

Chisholm acknowledges it can be tricky when a doctor disagrees with a patient's request for a fit note, and says there's support available for GPs so they can increase their skills in dealing with such issues.

"Consultations about health and work can obviously sometimes be difficult if there's a mismatch between the patient's and the GP's expectations about the best way forward," he says. "GPs would explain to their patient why they'd reached that conclusion, and why they felt it was in the patient's best interests to remain in or return to work."

SICK SENSE The amount of sick leave British workers take is actually falling, says the TUC. However, they also highlight that people struggling to carry on with work when they'd actually be better off staying home sick is equally problematic.

"Just as bad as sickness absence is the opposite - presenteeism - which is when people go in to work when they shouldn't be there because they're ill," says Hugh Robertson, head of health and safety at the TUC.

"It's a growing problem... If someone has a cold, do you really want them coming in when they're not well? They're not going to perform properly, and they're going to spread germs all over the office."

A number of factors come into play here, including people battling on because they're committed to their jobs, but sometimes employees will feel pressured not to take time off. For instance, some employers have punitive measures that mean if workers miss more than a certain amount of days per year, they don't get their contract renewed.

"So you're going to go in regardless of whether you've got the lurgy or not - and the result can be that you make yourself even more ill," says Robertson.

"Being off sick when you are sick is not a bad thing. It's not immoral - you need to work with your employer towards getting well so you can go back to work."

FAKING IT?

Robertson acknowledges that some employers believe staff take time off sick unnecessarily, but points out that if this is really a concern, perhaps they should be asking themselves why.

"If you ask employers, they think half their staff are swinging the lead, and if you ask workers, they say they never do it," he observes.

"But if employers do have a considerable issue with short-term sickness absence, then the problem isn't with the workers, it's with the work. If people are so demoralised that they can't bring themselves to come into work, the employer should be looking at how they're treating their staff.

"If there's a positive environment at work, people feel rewarded, not just economically but also in other senses, and they'll want to come in."