Studies show that a sedentary lifestyle can slash life expectancy by seven years, but exactly what harm are you doing by lounging on the sofa after work?

The shocking claim that sitting down is as unhealthy as smoking, touted by journalists and scientists alike, makes you sit up and think twice about your daily routines, but you should blow smoke on the comparison. It is true that, just as smokers can’t repair all long-term lung damage by giving up, you won’t be able to undo all the ill effects of prolonged sitting just by doing some exercise. However, smoking is in an unhealthy league of its own. Few smokers are lucky enough to get into old age without suffering some kind of lung disease or cancer, whereas many desk workers lead a perfectly healthy life. Smoking increases your risk of dying each year by an average of 180 percent, while sitting down all day leads to a 25 percent increase.

Most people in developed countries now spend most of their waking hours on their posterior, and it’s taking a toll on our physical health. Even someone who exercises for 45 minutes each day probably spends most of their remaining 16 hours sitting. Commuting, working, and eating are all done in a seat, and evenings are often spent unwinding in front of a screen.

The more hours you sit every day, the more harm you do to your body. All this sluggishness cramps our concentration, increases fatigue, puts strain on the heart and circulation, alters the body’s internal chemistry, and accelerates fatty buildup in arteries.

Your body is built to move: its 200-plus bones, connected by 360 joints, clothed in a jacket of 700 muscles, hold you upright and propel you forward. This timeline shows how prolonged sitting compromises the body in different ways.

Want to limit the time spent on your behind?

■ Try a standing desk to improve blood flow, facilitate creative thinking, and boost alertness. If you can’t do that, take every opportunity to stand up—for instance, to speak to a colleague, make a call, or get a drink.

■ Go for a five-minute walk every hour, which will cancel out many of sitting’s negative health effects.

■ Find more active ways to unwind such as yoga, cooking, or DIY to balance leisure time spent on the couch and encourage your brain to release mood-boosting hormones.