Association of Daily Sitting Time and Leisure-Time Physical Activity With Survival Among US Cancer Survivors

IMPORTANCE Sedentary behaviors, particularly prolonged sitting and lack of physical activity, may influence survival after cancer. OBJECTIVE To examine the independent and joint associations of daily sitting time and leisure-time physical activity with mortality outcomes among cancer survivors. DESIGN, SETTING, AND PARTICIPANTS A prospective cohort of a nationally representative sample of cancer survivors, age 40 years or older (n = 1535; weighted population, 14 002 666), from the US National Health and Nutrition Examination Survey from 2007 to 2014. Participants were linked to mortality data from their interview and physical examination date through December 31, 2015. Daily sitting time and leisure-time physical activity (LTPA) were self-reported using the Global Physical Activity Questionnaire. Data analyses were performed from January 1 to May 1, 2021. MAIN OUTCOMES AND MEASURES All-cause, cancer-specific, and noncancer mortality. RESULTS Among 1535 cancer survivors (mean [SE] age, 65.1 [0.4] years; 828 [60.1%] females; 945 [83.1%] non-Hispanic White individuals), 950 (56.8%) reported LTPA of 0 minutes per week (min/wk) during the previous week (inactive); 226 (15.6%) reported LTPA of less than 150 min/wk (insufficiently active); 359 (27.6%) reported LTPA of 150 min/wk or more (active); 553 (35.4%) reported sitting for 6 to 8 hours per day (h/d); and 328 (24.9%) reported sitting for more than 8 h/d. Of note, 574 (35.8%) cancer survivors reported no LTPA with concurrent sitting of more than 6 h/d. During the follow-up period of up to 9 years (median, 4.5 years; 6980 person-years), there were 293 deaths (cancer, 114; heart diseases, 41; other causes, 138). Multivariable models showed that being physically active was associated with lower risks of all-cause (hazard ratio [HR], 0.34; 95% CI, 0.20-0.60) and cancer-specific (HR, 0.32; 95% CI, 0.15-0.70) mortality compared with inactivity. Sitting more than 8 h/d was associated with higher risks of all-cause (HR, 1.81; 95% CI, 1.05-3.14) and cancer-specific (HR, 2.27; 95% CI, 1.08-4.79) mortality compared with those sitting less than 4 h/d. In the joint analyses, prolonged sitting was associated with an increased risk of death among cancer survivors who were not sufficiently active. Specifically, inactive and insufficiently active survivors reported sitting more than 8 h/d had the highest overall (HR, 5.38; 95% CI, 2.99-9.67) and cancer-specific (HR, 4.71; 95% CI, 1.60-13.9) mortality risks. CONCLUSIONS AND RELEVANCE In this cohort study of a nationally representative sample of US cancer survivors, the combination of prolonged sitting with lack of physical activity was highly prevalent and was associated with the highest risks of death from all causes and cancer.