Why should I avoid sitting down all day?

Spending a long time sitting around can be hazardous to your longevity, even if you're active sometimes. Here's what you need to know.

The term "couch potato" is an amusing description of those people who almost never abandon their widescreen TVs or computer monitors for anything other than basic biological necessities. But even if you get to the gym for an occasional workout doesn't mean that you may not be a bit of a spud yourself. And it's no joke.

That's according to researchers at the American Cancer Society, who investigated the link between how much time people spend sitting around and their overall mortality. Looking over a 13-year history, the scientists found that the more time you stay planted on your rear can reduce the time you're destined to live on the planet.

This was more true for women than men. Women who reported more than six hours per day of sitting (outside of work) were 37% more likely to die during the 13-year study than those who sat fewer than three hours a day. Men who sat more than six hours a day (also outside of work) were 18% more likely to die than those who sat fewer than three hours per day. Interestingly, those who reported they were physically active also had troubling mortality rates if they were acting like human lounge chairs for six hours a day.

Let's say you don't exercise. Then you're really cutting years off your life. Women and men who sat more and were less physically active were 94% and 48% more likely to die during the 13-year study period, respectively.

The researchers believe that the long stretches of being sedentary negatively affect the metabolic processes in your body, endangering your cardiovascular system and cells. These results also tell us an important, inescapable fact: Fitness is a lifestyle, not an occasional fling.