Spending too much time sitting down is believed to increase mortality even if you exercise regularly.

E.g. http://www.health.harvard.edu/blog/too-much-sitting-linked-t...:

“Even if you are doing the recommended amount of moderate to vigorous exercise, you will still have a higher risk of mortality if you’re spending too many hours sitting,” says Dr. JoAnn Manson, one of the study’s authors, and chief of preventive medicine at Harvard-affiliated Brigham and Women’s Hospital.