Prolonged sitting time increases the risk of colon, endometrial, and lung cancers
Sedentary behavior refers to activities that do not increase energy expenditure substantially above the resting level and includes activities such as sleeping, sitting, lying down, and watching television, and other forms of screen-based entertainment. Lack of physical activity has clearly been shown to be a risk factor for cardiovascular disease and other conditions.
The evidence relating to television viewing and other sedentary behaviors to cancer risk has not been significantly summarized.
Dr. Daniela Schmid, PhD, MSc, and Dr. Michael F. Leitzmann, MD, Dr Ph, of the Department of Epidemiology and Preventive Medicine, University of Regensburg, Germany, conducted a search in Cochrane, EMBASE, Medline, and SciSearch databases through February 2014 for published articles that examined sedentary behavior in association to cancer risk.
The meta-analysis had included over four million participants of 43 observational studies and 68,936 cancer cases. Information from individual studies had been obtained with self-administered questionnaires and through interviews.
Comparing the highest vs lowest levels of sedentary time, the relative risks the researchers had found a statistical higher risk for three types of cancer; colon, endometrial, and lung. The risk for colon cancer was 1.54 (95% confidence interval [CI] = 1.19 to 1.98) for TV viewing time, 1.24 (95% CI = 1.09 to 1.41) for occupational sitting time, and 1.24 (95% CI = 1.03 to 1.50) for total sitting time. For endometrial cancer, the relative risks were 1.66 (95% CI = 1.21 to 2.28) for TV viewing time and 1.32 (95% CI = 1.08 to 1.61) for total sitting time. A positive association with overall sedentary behavior was also noted for lung cancer (RR = 1.21; 95% CI = 1.03 to 1.43).
The risk for cancer increased with each 2-hour increase in sitting time’; 8% for colon cancer, 10% for endometrial cancer, and 6% for lung cancer, although the last was borderline statistically significant. This effect had appeared to be independent of physical activity which suggests that large amounts of time spent sitting can still be detrimental to those who are otherwise physically active.
Television viewing time had the strongest association to colon and endometrial cancer, According to the authors this could be due to the fact that television viewing is often associated with consuming sweetened beverages and junk food.
Sedentary behavior was unrelated to cancers of the breast, rectum, ovaries, prostate, stomach, esophagus, testes, renal cell, and non-Hodgkin lymphoma.
The researchers write "That sedentariness has a detrimental impact on cancer even among physically active persons implies that limiting the time spent sedentary may play an important role in preventing cancer.”
In an accompanying editorial, Lin Yang, Postdoctoral Research Associate at the transdisciplinary research on energetics and cancer (TREC) center in the School of Medicine in Washington University in St. Louis and Dr. Graham A. Colditz, MD, Dr. PH, Associate Director, Prevention and Control, Alvin J. Siteman Cancer Center, and Niess-Gain Professor in the School of Medicine, Department of Surgery, Washington University School of Medicine write that these results "…support a causal relation between sedentary behavior and both colon and endometrial cancers." They comment that cancer prevention requires good evidence, political will, and a social strategy to fund and implement prevention programs.
This study is published in JNCI Journal of the National Cancer Institute.