Depression is a common reasons for sick leave
People who have long spells of sick leave for psychiatric reasons are twice as likely to die from cancer as healthier employees, research suggests.
The "unexpected" finding could help pick out at-risk groups, the University College London researchers reported in the British Medical Journal.
Among 6,500 civil servants, those who had taken a long period of sick leave had a 66% higher risk of early death.
The cancer risk may be due to depressed people not seeing a doctor soon enough.
Sickness records were assessed from London-based employees in 20 Whitehall departments between 1985 and 1988 and compared with mortality up until 2004.
Overall 288 people died during the study.
The 30% of people who had one or more stints of at least seven days off work had a 66% increased risk of premature death compared to those who had not had any long periods of sick leave, it was found.
The highest mortality risk was seen in those who had been off work with heart disease, stroke or related conditions who had more than four times the risk of premature death than those who had no long sickness absences.
Perhaps more surprisingly, absences due to common respiratory conditions and infections were also associated with an increased risk of death, the researchers said.
Study leader Jenny Head said it was the first time work absence for psychiatric reasons such as depression had been linked to death from cancer.
"That was the unexpected finding," she said.
"We didn't study the reason, but it might be people that tend to be depressed might be less likely to seek help from a doctor or being prone to depression could affect your cancer prognosis or depression might affect adherence to treatment."
She added: "It would be useful for this information to be collected because we could identify groups with high risk of serious health problems".
An accompanying editorial in the BMJ suggested that information on sickness absence could provide GPs with a useful tool to identify workers with an increased risk of serious illness or risk of death.
Employers could also use the information to target help for work-related health problems such as stress, it said.
Dr Stuart Whitaker, senior lecturer in occupational health at the University of Cumbria, said: "It would seem sensible to expect that those who do take longer and more frequent periods of sickness absence are suffering with more severe health problems, than those who do not go off sick, and might be expected to have higher premature death rates.
"This study helps to demonstrate that and goes further in being able to show the increased risk for different types of conditions."
However he added more work was needed to determine how occupational health services could identify those at high risk and what interventions they would then use to prevent early death.