Can someone be "healthier" by doing exercise when they are a smoker? Of course. But it will never compete with an active non-smoker. If it is the same case with "sitters" than it's a very alarming situation. From the Mayo Clinic article:
One study compared adults who spent less than two hours a day in front of the TV or other screen-based entertainment with those who logged more than four hours a day of recreational screen time. Those with greater screen time had:
- A nearly 50 percent increased risk of death from any cause
- About a 125 percent increased risk of events associated with cardiovascular disease, such as chest pain (angina) or heart attack
http://www.mayoclinic.org/healthy-lifestyle/adult-health/expert-answers/sitting/faq-20058005