More NHS staff take sick leave in areas of high deprivation in England, Audit Commission figures suggest.
The report looked at data collected between July 2009 and June 2010.
It also found junior staff were more likely to take time off than senior colleagues: healthcare assistants had the highest average absence rate, followed by ambulance staff.
Professor Dame Carol Black, national director for health and work, said the findings would "prompt reflection".
There are wide variations around the country when it comes to NHS sickness absence, with some organisations having a rate of 1.6% and others reporting 6.8%.
Healthcare assistants have the highest average rate of absence taking off 6.5% of their working time, followed by ambulance staff at 6.3%, and nurses, midwives and health visitors at 5.2%.
Overall, the North East has the highest sickness rate on average, with the lowest seen in London.
Mental health and learning disability trusts, as well as ambulance trusts have some of the highest rates, according to the study from the Audit Commission.
It says the NHS could save £290m if sickness absence rates were reduced to the lowest 25%.
Staff sickness absence in the NHS is estimated to cost £1.7bn a year, and is higher than in the private sector.
Deprivation and staff pay grade account for 61% of the variation in hospital trust absence and 38% in primary care trusts (PCTs), according to the study.
Experts are unclear exactly why deprivation and pay scale influence absence rates so much, although "morale and ability to control one's work" may play a role for those who are lower paid.
Professor Dame Carol Black said the unexplained variations between trusts highlighted the importance of good management practice "in minimising the causes of sickness absence of staff at every level".
"The findings of the report will prompt reflection in every trust, and review with remedial action in many," she said.
A British Medical Association spokesperson said: "Regional variations in levels of absence attributable to sickness exist in every sector - not just the NHS.
"Over the last decade, there have been large reductions in absence rates in the public sector as a whole. These have been reflected in the NHS, despite funding cuts, staff shortages, and increased activity and pressure."
Paramedic Jonathan Fox, spokesman for the Association of Professional Ambulance Personnel, said he was unsurprised ambulance personnel had among the highest rates for sickness leave and was critical of the "unsustainable demand" being put on people.
Increasing 999 calls, response times and individual performance targets had all conspired to put unprecedented pressure on ambulance staff.
"And when they are ill there is a tacit pressure on staff to stay at work. People are being coerced to stay to work because they are put on monitored attendance.
"People are forgetting that their most precious asset is their frontline people, who are human beings. They are being pushed and pushed."
Dr Peter Carter, chief executive and general secretary of the Royal College of Nursing (RCN), which represents healthcare workers, said: "We need a step change in the way the NHS manages staff health and wellbeing. With over 10 million working days lost each year and staff working when they are not well enough, the quality of patient care will inevitably suffer.
"Good occupational health services can often make a big difference if all staff have access to them. We look forward to working with the government and employers to deliver this."
A spokesperson for the Department of Health said: "A healthier NHS is a more productive NHS and NHS organisations should do all they can to make sure their staff are in the best possible health.
"Across the NHS, average sickness rates are improving, but more needs to be done. If we can reduce sickness levels by just one third, we could see productivity gains of up to £555 million per annum."