One way to view activity level and health outcome is to measure health outcomes based on amount of non-active time. However, caution must be used in interpretation because moderate activity as recommended is not necessarily the opposite of being sedentary. A meta-analysis assessed sedentary time with risk for disease, mortality and hospitalization. This, in combination with studies on moderate and vigorous activity, helps to provide a more complete picture of activity level and health outcomes.
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“Maintaining a minimum amount of physical activity and breaking up sedentary time with walks or non-sitting tasks would appear to be beneficial to health.”
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The study defined being sedentary as less than 1.5 METS (eg. sitting, watching TV, reclining) and evaluated overall hours of sedentary behavior or sitting hours per day or week. Out of almost 21,000 studies 41 met inclusion criteria. The analysis found that greater sedentary time was associated with all-cause mortality, cardiovascular disease incidence, cancer incidence and type 2 diabetes incidence. Of the cancers, breast, colon, colorectal, endometrial and epithelial ovarian cancers showed increased incidence. Further, sitting fewer than eight hours a day had a 14% lower risk for potentially avoidable hospital admissions. When evaluating sedentary time along with level of activity, there was a 30% less relative risk of all-cause mortality in those with high versus low levels of physical activity. It appears that there is an interaction between amount of non-activity and amount of activity, with those who are more physically active having less impact of sedentary time on their health.
Based on this analysis, both activity and non-activity time is important. Currently guidelines do not state how much sedentary time is “acceptable.” The amount may be different if sitting at work versus sitting in leisure time. We also don’t know if being sedentary and awake longer is better or worse than sleeping more. Much more research is needed. In the meantime, maintaining a minimum amount of physical activity and breaking up sedentary time with walks or non-sitting tasks would appear to be beneficial to health.