Sitting is bad !
Sitting in front of TV or computer for hours on end
is really bad !
That's the message.

As we get older, this is really important to remember.
I've been telling my old patients and young patients  for some time that
they must get up every half an hour no matter what.

I think this would apply to all of us.

Thanks for the information.  KJ

They have developed "standing chair" for the office workers who must be sitting all day.
It's relieving to hear that "less than 4 hours a day" may be OK.
I will have to limit my sitting time not to be longer than 4 hours.
That is cutting the computer time shorter.

I wish if they have a study to see if extra-walking (or standing excercises) could negate the bad effect of sitting,
as some of this sittings can not be avoided in the course of making a living.

WM,
This study stated specifically that the sitting hours are independent of the physical activity levels,
which was surprising to me as well.
In other words, it is regardless of fitness levels.
Before I read this study, I thought that my daily exercise will negate or neutralize the bad effects
of sitting.

Another systemic review of the relationship between occupational sitting time and
health outcomes suggested that individuals with more active jobs had lower all-cause or
cardiovascular mortality risk than those with jobs that involved mostly sitting.(van Uffelen et al,
Am J Prev Med 2010, 39(4) 379-388, Occupational Sitting and health Risk)

This study quoted here shows a clear dose-response relationship for sitting time and physical activity
with all-cause mortality. Inactive participants with high levels of sitting had the highest mortality rate,
and the strong relationship of increased sitting time to mortality persisted, even among participants
with relatively high levels of physical activity.
As expected, healthy participants had lower absolute all-cause mortality rates compared with preexisting
cardiovascular disease or diabetes, and increased physical activity and reduced sitting were associated
with reduced rates in both groups.

The adverse effects of prolonged sitting are thought to be mainly owing to reduced metabolic and vascular health.
Prolonged sitting has been shown to disrupt metabolic function, resulting in increased plasma triglyceride
levels, decreased levels of HDL, decreased insulin sensitivity, and change in
muscle glucose transporter protein content.

Results from molecular biology and medical chemistry studies have suggested that
physical activity and sedentary behavior have different influences on the body,
supporting their independent effects on health.
This study quoted here seems to show clearly the association between sitting and all-cause mortality
that was independent of physical activity.
The findings persisted after adjustment and stratification for BMI and
appear to be independent of BMI as well.

Hopefully, I answered your question to your satisfaction.
All of the above were discussed in the article quoted here, and
I simply either copied or slightly paraphrased with references available in the article.