Repeatedly going to work when ill significantly boosts the chances of having to take long term sick leave later on, reveals research published ahead of print in the Journal of Epidemiology and Community Health.

Going to work when ill is an increasingly recognised phenomenon known as "sickness presence," but relatively little is known about the long term impact of this behaviour.

The researchers randomly selected almost 12,000 Danes of working age, who had been in continuous employment for at least a year, to answer questions on their attitudes to work, preparedness to take time off when ill, and general health.

They were asked how many times in the preceding year they had gone to work ill when it would have been reasonable to have stayed at home.

Their responses were married up with official records detailing periods of sick leave taken, and lasting at least a fortnight, over the next 18 months.

Poor general health, a heavy workload, work-family life conflicts, a good level of social support, holding a senior post, and obesity featured most often among those who repeatedly came to work, despite being ill.

Workers who had done this at least half a dozen times were 53% more likely to end up going off sick for two weeks, and 74% more likely to take more than two months of sick leave, compared with those who did not come to work when ill.

These findings held true even after taking account of known risk factors for long term sick leave, previous bouts of lengthy sickness absence, and prevailing health.

Short periods off sick may allow workers to cope better with the stresses of a demanding job, and, overall, the evidence is that employment is good for health, say the authors. But long term sick leave is associated with difficulties finding work, they warn.

For more information on the BMJ-British Medical Journal, visit www.bmj.com.