How much time you spend sitting may affect your risk of dying earlier more than how much physical activity you get, says a new study from the American Cancer Society. Researchers say the amount of time sitting was associated with mortality, regardless of the level of physical activity.

The growing epidemic of obesity and overweight has been linked to reduced physical activity. And while studies support a link between time spent sitting and obesity, Type 2 diabetes, and cardiovascular disease, few studies have looked at the association between sitting and mortality.

The study, which was published in the American Journal of Epidemiology, surveyed 123,216 individuals, who had no history of cancer, heart attack, stroke, or emphysema, between the years of 1993 and 2006. They found that women who sat more than six hours daily increased their risk of dying during the time period by 37 percent when compared to women who sat less than three hours each day. Men who sat more than six hours a day were 18 percent more likely to die during the time period.

Even after adjusting for activity levels, the association remained the same. Links were stronger for cardiovascular disease mortality than for cancer mortality.

"Several factors could explain the positive association between time spent sitting and higher all-cause death rates," said Alpa Patel, Ph.D. "Prolonged time spent sitting, independent of physical activity, has been shown to have important metabolic consequences, and may influence things like triglycerides, high density lipoprotein, cholesterol, fasting plasma glucose, resting blood pressure, and leptin, which are biomarkers of obesity and cardiovascular and other chronic diseases."

The authors of the study concluded that "public health messages and guidelines should be refined to include reducing time spent sitting in addition to promoting physical activity. Because a sizeable fraction of the population spends much of their time sitting, it is beneficial to encourage sedentary individuals to stand up and walk around as well as to reach optimal levels of physical activity."

Heart disease is the leading cause of death in the United States, and, according to the Centers for Disease Control and Prevention, is responsible for more than 631,000 deaths annually. Approximately 550,000 Americans die of cancer each year.