From the January 15, 2014 Science Daily:
Led by Cornell University nutritional scientist Rebecca Seguin, a new study of 93,000 postmenopausal American women found those with the highest amounts of sedentary time -- defined as sitting and resting, excluding sleeping -- died earlier than their most active peers. The association remained even when controlling for physical mobility and function, chronic disease status, demographic factors and overall fitness -- meaning that even habitual exercisers are at risk if they have high amounts of idle time.
Seguin and co-authors found that women with more than 11 hours of daily sedentary time faced a 12 percent increase in all-cause premature mortality compared with the most energetic group -- those with four hours or less of inactivity. The former group also upped their odds for death due to cardiovascular disease, coronary heart disease and cancer by 13, 27 and 21 percent, respectively.
The assumption has been that if you're fit and physically active, that will protect you, even if you spend a huge amount of time sitting each day," said Seguin, assistant professor of nutritional sciences in Cornell's College of Human Ecology. "In fact, in doing so you are far less protected from negative health effects of being sedentary than you realize."