According to researchers at the Karolinska Institute in Stockholm, participants in the study were 2.5 times more likely to call in sick on days they expected to have a light workload, compared with days when they had a normal workload.
They found that the risk for was even higher if workers' doldrums had started the day before they called in sick.
"Our results indicate that nonmedical factors may have trigger effects on short-term sick leave," the researchers said.
One reason for the findings may be that employees are less satisfied with their jobs when they're twiddling their thumbs, and so they're less motivated to show up to work when feeling ill.
Another idea is that bosses might encourage their coughing and sneezing employees to stay home when the workload is light.
In addition, the findings may not be generalizable to people in all work fields - employees in the study who worked for a manufacturing plant were more likely to have slow days than those who worked in the health care field or office workers.
The researchers said that larger studies are needed to determine the effect of workload on employee sick days in different occupations.
The study involved 1,430 employees at six Swedish workplaces who were followed for three to 12 months. Of these, 546 took a day off over the study period.
Employees were interviewed during their time off, and asked whether they had experienced a slow work day anytime during the two-week period prior to the sick day, and on the sick day itself.
The researchers noted having a light workload was not common among participants. Of those who took sick leave, 88 percent said they had not experienced a slow work day in the two weeks leading up to their sick day.
They said that this suggests that the effect of a light workload on taking sick leave, while real, may be quite small.
The study has been published in the Journal of Occupational and Environmental Medicine.