Does smoking increase sick leave? Evidence using register data on Swedish workers.

OBJECTIVE: To examine the effect of smoking on sick leave.
METHODS: Nationally representative data on 14,272 workers aged 16-65 years from the 1988-91 waves of the Swedish Survey of Living Conditions were used for the analyses. The data are linked to register-based data, on the annual number of absences due to sickness, from the National Board of Social Insurance. As outcome variable, the annual number of days of sick leave was used. This outcome was analysed as a function of smoking status and an extensive number of control variables, including occupational risk factors, work characteristics and health status.
RESULTS: Smoking was found to increase the annual number of days of absence by 10.7 compared with never smoking. Controlling for risk factors at work, and thereby accounting for some of the selection of smokers into riskier jobs, reduced the effect to 9.7 days, corresponding to 38% of all annual absences due to sickness. Moreover, controlling for health status further reduced the effect of smoking to 7.7 days. The effect of smoking on sick leave was similar for men and women.
CONCLUSIONS: Smoking showed a large positive effect on the annual number of sick leaves. Hence, the results suggest that the gains to preventing and/or reducing smoking, in terms of reduced production losses, may be large. However, since the large effect of smoking persists when controlling for a range of health factors and occupational factors, the results also suggest that much of the higher number of absences among smokers may be explained by factors other than reduced health. The estimates should be viewed as upper bounds of the effect of smoking on sick leave, since smoking is potentially an endogenous variable.