Here is why
Let's compare transit drivers, who sit most of the day, and conductors or guards, who don't. Though diets and lifestyles are a lot similar of both groups, the drivers are about twice as likely to get heart disease than the other groups. It is just because of sitting.
People who sit for long hours continuously are more likely to die earlier from any disease. Exercise helps a little in these cases. Sitting elevates the risk of heart disease, diabetes, stroke, high blood pressure, and high cholesterol.
The bad effects of too much sitting are very difficult to counter with exercise. You hardly can reverse the effects of sitting 7 hours at a time.
Surprisingly, you are more likely to have diabetes if you sit all day. It also contributes to obesity and anxiety.
Deep Vein Thrombosis (DVT), a clot that forms in the leg, often forms due to long time sitting. It can be serious if the clot travels and lodges in the lungs. Sometimes, it exhibits no symptom.
The prolong sitting habit puts heavy pressure on your back muscles, neck, and spine. An ergonomic chair may not ease the problem. You need to get up and move around for a minute or two every half hour to keep your back healthy.
The senior citizens who are inactive may be more likely to develop osteoporosis (problem with weak bones) and could gradually become unable to do the basic tasks of everyday life, like bathing or using toilets.
Your chance of developing different kinds of cancers increases due to sitting more. The more you sit, the higher your odds are.
The only remedy is to be more active and move on. You need to stand up and stretch every half hour or so. You can touch your toes. Take a stroll around places. You can arrange a treadmill at your workplace. All these things can help prevent the bad effects of uninterrupted sitting and keep you a healthy life.
Source: World Health Organisation