Researchers analyzed data from 93,000 postmenopausal American women. They found that women who spent more than 11 hours a day sitting or otherwise being inactive had a 12 percent higher risk of premature death from all causes than those who were inactive for four hours or less per day.
Women who were inactive also were 13 percent more likely to die of cardiovascular disease, 21 percent more likely to die of cancer and 27 percent more likely to die of coronary heart disease, according to the study.
The women were 50 to 79 years old at the start of the study and were followed for 12 or more years. The findings were published online in the American Journal of Preventive Medicine.
"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," study leader Rebecca Seguin, an assistant professor of nutritional sciences at Cornell University, said in a university news release. "[But] in doing so, you are far less protected from negative health effects of being sedentary than you realize."
Seguin said women begin to lose muscle mass at age 35, and that loss accelerates with menopause. Although working out regularly, especially with weights, can help counteract that effect, it's also important for women to incorporate more everyday movement in their lives.
"In general, a use-it-or-lose-it philosophy applies," Seguin said. "We have a lot of modern conveniences and technologies that, while making us more efficient, also lead to decreased activity and diminished ability to do things. Women need to find ways to remain active."
Starting in middle age and even younger, women can make "small changes that make a big difference," she said.
"If you're in an office, get up and move around frequently," Seguin said. "If you're retired and have more idle time, find ways to move around inside and outside the house. Get up between TV programs, take breaks in computer and reading time, and be conscious of interrupting prolonged sedentary time."
Although the study showed a connection between older women sitting more and higher risk of early death, it didn't establish a cause-and-effect relationship.
The U.S. Office on Women's Health has more about physical activity.