Replace Sedentary Time With Activity

Arem and colleagues analyzed the dose-response relationship, if any, between the amount of exercise performed and the risk for mortality. Their results were published in the June 2015 issue of JAMA Internal Medicine.^[1]

Researchers pooled data from 6 studies to create a cohort of 661,137 adults with a median age of 62 years. Compared with adults reporting no physical activity, adults who were active but failed to meet the national recommendation for activity experienced a 20% lower risk for mortality (hazard ratio [HR]=0.8 [95% CI: 0.78, 0.82]). The respective HRs among adults who completed exercise at 1 to 2 times the minimum threshold and among adults who exercised at 2 to 3 times this minimum were 0.69 (95% CI: 0.67, 0.7) and 0.63 (95% CI: 0.62, 0.65). There was a minimal improvement in mortality when comparing basic compliance with the minimum activity threshold with high levels of exercise, although exercise at high levels was not harmful in terms of mortality risk. Physical activity was similarly effective in the prevention of death because of cardiovascular disease (CVD) and cancer.

There has been much attention paid recently to sedentary time and its deleterious effects on health. What is the minimum amount of physical activity required to replace sedentary time in order to improve mortality outcomes? The current study by Rees-Punia focused on this issue.

Study Synopsis and Perspective

Cutting back on sitting time and replacing it with even light physical activity (LPA) could potentially reduce the risk for premature death, according to new findings.

Replacing 30 min/d of sitting time with either LPA or moderate to vigorous physical activity (MVPA) was associated with a lower risk for mortality, although this varied according to activity level.

Among adults who were low to moderately active, replacing sitting with LPA was associated with a reduction in cancer, CVD, and all-cause mortality. Greater mortality benefits were observed when sitting time was replaced with MVPA.

The study was published March 21 in the American Journal of Preventive Medicine.^[2]

"The take-home message is that replacing some sitting time with even light intensity physical activities, such as gardening or taking a leisurely walk, may be beneficial for those who are currently inactive, and replacing sitting time with more intense physical activities is associated with even greater health benefits," said lead author Erika Rees-Punia, PhD, MPH, a postdoctoral fellow at the American Cancer Society (ACS).

Replacing 30 min/d of sitting with LPA was associated with a 14% reduced risk for death whereas MVPA was associated with a 45% reduced risk for death among persons who were inactive, she explained.

"In our study, this included participants who exercise 17 minutes per day or less," she continued.

The benefit was less pronounced among adults who were less sedentary.

"For those who are a little more active, replacing 30 minutes a day of sitting with light intensity physical activity was associated with a 6% reduced risk of death, while replacement with [MVPA] was associated with a 17% reduced risk of death," Dr Rees-Punia told Medscape Medical News.

More Activity, Better Results

Physical activity has been associated with a lower risk for certain cancers as well as CVD and premature death. A large and ever growing body of evidence has demonstrated the benefits of exercise in helping to mitigate cancer risk and in improving outcomes in patients with cancer, both during and after active treatment.

The authors noted that most previous studies have explored the potential effect of sedentary time without considering the physical activity it displaces and thus leaving a gap in the understanding of the issue. In this study, Dr Rees-Punia and colleagues looked at the estimated mortality risks associated with replacing 30 min/d of sitting time with either LPA or MVPA.

The cohort included 92,541 individuals who participated in the ACS Cancer Prevention Study-II Nutrition Cohort, and the analysis reviewed sedentary time and activity levels over a period of 15 years (1999-2014). A total of 14,415 men and 13,358 women died during the follow-up period.

Participants who reported higher levels of activity tended to be more highly educated and were less likely to be current smokers. Sedentary time primarily included watching TV (39%) and reading (20%).

Overall, switching 30 min/d of sitting to LPA (hazard ratio [HR]=0.94) or MVPA (HR=0.92) was associated with significant reductions in the risk for mortality, but replacing sitting with LPA was associated with a reduced mortality risk only for adults who were only minimally (HR=0.86) and moderately (HR=0.94) active but not for adults who were highly active.

Greater benefits were observed when sitting time was replaced with MVPA (low active, HR=0.55; moderately active, HR=0.83).

Similar results were seen for cancer mortality with LPA (low active, HR=0.9; high active, HR=1.01) and for MVPA (low active, HR=0.53; high active, HR=1).

The findings were similar when stratified by sex and body mass index (BMI), but significant interactions by age showed larger mortality benefits for older adults who replaced sitting with LPA.

"We did explore the role of age on the replacement of sitting time and found that older adults, 75 years and above, may benefit from replacing sitting time with light-intensity physical activity more than younger adults," said Dr Rees-Punia.

The ACS funded the Cancer Prevention Study-II. Rees-Punia and study coauthors have disclosed no relevant financial relationships.

Clinical Implications

• In a previous study by Arem and colleagues, even low levels of physical activity were associated with a mortality benefit compared with no physical activity among older adults. There was a minimal improvement in mortality in comparing basic compliance with physical activity guidelines with high levels of exercise.
• In the current study by Rees-Punia and colleagues, replacing 30 minutes of sedentary time with either LPA or MVPA was associated with a lower risk for mortality among older adults. In particular, adults at age 75 benefited from less sedentary time, but the mortality benefit associated with reducing sedentary time did not apply to adults with high baseline levels of physical activity.
• Implications for the Healthcare Team: The healthcare team should promote even mild amounts of LPA among adults to promote greater longevity.