A new study is revealing the most important factor for a healthy life.

It turns out exercise is more important than eating healthy or not smoking.

Research in the journal JAMA found that those with a more sedentary lifestyle are five times more likely to suffer premature death than those who are extremely fit.

Those who performed poorly on a treadmill had almost double the mortality risk as someone on dialysis.

Doctors say this is a reminder that anyone, no matter what age, can start walking, or running, to a longer life.