Why would sitting for just a short time be dangerous?

When you are sitting, the reduced muscular activity of the legs is decreasing the blood flow in the legs, deforming arterial segments. This is causing a decrease in shear stress of these arteries, causing reduced bio-availability of nitric oxide which again is increasing oxidative stress. The end result is impaired endothelial function.(Thosar S, et al. 2012). The endothelium is the inner lining of the blood vessels.

 
This is not only a local reaction in the arteries of the legs because the endothelium needs the stimulation of the blood flow to stay healthy. This is one way you may end up with atherosclerosis after awhile. If you want know more in detail about this, click on the reference below.

That’s why I designed the exercise program “Exercise for Maximum  Benefits” the way I did, taking this into consideration.

Is there anything you can take to help prevent this if you don’t exercise?
Actually, there is.

Curcumin, the active ingredient in the Indian spice Turmeric, has been shown to equally increase flow-mediated dilation when compared to exercise.(Akazawa N, et al. 2012).
I would, however, not rely only on that, because another study showed that taking curcumin in addition to exercise was superior to exercise by itself or taking curcumin by itself (Sugawara J, et al. 2012),
 

Just remember that curcumin is not well absorbed, so if you are going to take it, be sure you use a formula proven to be better absorbed than regular curcumin.