Introduction:
Prolonged sitters are not necessarily inactive. Smokers could be either physically inactive or found to be prolonged sitters. These behaviors added extra risk to them.

Objectives:
The objective of this study is to quantify the excess mortality risks and shortened life span among those either with inactivity or with prolonged sitting or both.

Methods:
A cohort, consisting of 422771 adults, was recruited successively during health surveillance between 1996 and 2008. Data from questionnaire, and results from fasting blood, urinalysis and other screening tests were collected. Hazard ratios (HR) came from Cox model and life expectancy from life table method.

Results:
One half of the cohort were either physically inactive (52%) or prolonged sitters (56%) with one third of current smokers (23.2%). HR for all-cause mortality for smoking, 1.51, for inactive, 1.55, for sitters, 1.23 but 1.78 for smoking sitters, 2.29 for inactive smoker and 2.76 for inactive smoking sitters. Life span shortened 6 years for smokers, 5 years for the inactive, 2 years for prolonged sitters, 8 years for inactive sitters, 9 years for inactive smokers, 7 years for sitting smokers, and 15 years for smokers with both inactivity and prolonged sitting.

Conclusion(s):
Inactive smokers, with prolonged sitting, could double the life years loss of smokers by losing as many as 15 years, in contrast to average loss of 6 years for smokers. That inactive sitters doubled the risk of smokers could be used to motivate either smoking cessation or encouraging physical activity.