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.”

Worse still, Seguin said, excess sedentary time tends to make it harder to regain physical strength and function. Women begin to lose muscle mass at age 35, a change that accelerates with menopause. Regular exercise, especially lifting weights and other muscular strength-building exercises, helps to counteract these declines, but her research finds that more everyday movement on top of working out is also important for maintaining health.

“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, Seguin said, women can adopt “small changes that make a big difference.”

“If you’re in an office, get up and move around frequently,” she 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.”

Though previous research has linked prolonged sedentary time with poor health outcomes, the study by Seguin is one of the largest and most ethnically diverse of its type. The women, ages 50-79 at the study’s outset as part of the national Women’s Health Initiative Study, were followed over 12 or more years.

The paper, “Sedentary Behavior and Mortality in Older Women,” was published online Jan. 7 in the American Journal of Preventive Medicine.