Study: Sitting Longer May Reduce Lifespan
In a recent study, epidemiologists from the American Cancer Society found that people who sit for more than three hours a day are more likely to have a shorter lifespan. Researchers said time spent sitting was independently associated with total mortality, regardless of physical activity level. The study appears in the American Journal of Epidemiology.
Physiologists who analyzed obesity, heart disease, and diabetes found that the act of sitting shuts down the circulation of a fat-absorbing enzyme called lipase. Standing up engages muscles and promotes the distribution of this enzyme, which prompts the body to process fat and cholesterol. They found that this was independent of the amount of time spent exercising and that standing up uses blood glucose, which may discourage the development of diabetes.
Dr. Alpa Patel, an epidemiologist for the American Cancer Society, and a team of researchers analyzed survey responses from 123,216 individuals (53,440 men and 69,776 women) who had no history of cancer, heart attack, stroke, or emphysema/other lung disease. They examined the amount of time spent sitting and physical activity in relation to mortality between 1993 and 2006. They found that more leisure time spent sitting was associated with higher risk of mortality, particularly in women. Women who reported more than six hours per day of sitting were 37 percent more likely to die during the time period studied than those who sat fewer than three hours a day. Men who sat more than six hours a day were 18 percent more likely to die than those who sat fewer than three hours per day. The association remained virtually unchanged after adjusting for physical activity level. Associations were stronger for cardiovascular disease mortality than for cancer mortality.
When combined with a lack of physical activity, the association was even stronger. Women and men who both sat more and were less physically active were 94 percent and 48 percent more likely, respectively, to die compared with those who reported sitting the least and being most active.
“Several factors could explain the positive association between time spent sitting and higher all-cause death rates,” Patel said. “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 noted 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.”