Now a new study says that spending too much time in a chair and depriving yourself of necessary sleep should join a short list of behaviors known to increase your risk of premature death.

Sedentary time and lack of sleep were damaging in their own right, but when combined with more traditional risk factors, they had a multiplier effect that made an early death far more likely.

The findings, published Tuesday in the journal PLOS Medicine, make clear that "some risk behaviors tend to cluster, particularly in certain patterns, and that the joint risk could be much higher than the sum of the individual risks," the study authors wrote.

For instance, smoking was the most dangerous single risk factor among the six studied — the small number of people for whom smoking was their only vice were 90% more likely to die during the course of the study than were people with practiced clean living across the board. People who reported high alcohol consumption — more than 14 alcoholic drinks per week — as their sole risk factor did not seem to be putting their lives in danger.