“With the increasing population of cancer survivors, there is an urgent need to identify feasible strategies to help enhance their long-term health,” Chao Cao, MPH, PhD-candidate explains. “Although Physical Activity Guidelines for Americans promotes that physical activity (PA) and exercise can benefit everyone, the evidence on health benefits of PA pertaining to patients with cancer is still limited. In addition, sedentary behaviors, such as prolonged sitting, have become highly prevalent in the last 2 decades and have gotten worse due to the COVID-19 pandemic. Cancer survivors who participate in our clinical studies frequently seek advice on changing their lifestyle behaviors to improve their health. Due to limited evidence, however, the current guideline did not have specific recommendations on sedentary behaviors with consideration of PA for cancer survivors.”

To address this knowledge gap, Cao and colleagues sought to evaluate the independent and joint associations of daily sitting time and leisure-time physical activity (LTPA) with mortality outcomes among cancer survivors. For a paper published in JAMA Oncology, the researchers conducted a prospective cohort study of a nationally representative sample of cancer survivors aged 40 and older (N=1,535; weighted population, 14,002,666), from the United States National Health and Nutrition Examination Survey (NHANES) from 2007 to 2014. Researchers linked mortality data from death certificate records according to the National Death Index up to the last day of 2015.

The study team used Cox regression models, adjusting for sociodemographic and lifestyle factors, to examine the association of sitting time and PA with risk for death due to cancer and other causes. “Specifically, we categorized the participants into joint categories based on sitting time and physical activity to compare the mortality risks across different levels of activity from the most active groups (meeting PA guidelines and sitting less than 6 hours per day) to most inactive groups (not meeting PA guidelines and sitting more than 8 hours per day),” Cao says.

Being Active Linked With Lower Risk of All-Cause Mortality

Cao and colleagues found that the combination of protracted sitting with the absence of PA was highly widespread in cancer survivors and was associated with increased all-cause and cancer-specific mortality risks. Among all cancer survivors, 56.8% reported LTPA of 0 minutes per week (minutes/week) during the previous week (inactive); 15.6% reported LTPA of less than 150 minutes/week (insufficiently active); 27.6% reported LTPA of 150 minutes/week or more (active); 35.4% reported sitting for 6 to 8 hours per day; and 24.9% reported sitting for more than 8 hours per day. Notably, 35.8% of cancer survivors reported no LTPA with simultaneous sitting of more than 6 hours per day. Over a follow-up period of up to 9 years (median, 4.5 years; 6,980 person-years), there were 293 deaths (cancer, 114; heart diseases, 41; other causes, 138).

“Our multivariable models show that being physically active was associated with decreased risks of all-cause and cancer-specific mortality compared with inactivity,” Cao notes. “Sitting more than 8 hours per day was associated with higher risks of all-cause and cancer-specific mortality compared with those sitting less than 4 hours per day. In the joint analyses, extended sitting was associated with a greater risk for death among cancer survivors who were not adequately active. Specifically, inactive and insufficiently active survivors who reported sitting more than 8 hours per day had the greatest overall and cancer-specific mortality risks.”

75% of Survivors Did Not Meet Physical Activity Guidelines

A critical issue, Cao points out, is that nearly three out of four US cancer survivors did not meet the Physical Activity Guidelines and most of them sat more than 6 hours per day (Figure). “Due to these facts, avoiding prolonged sitting is essential for most cancer survivors,” Cao says. “And, for most cancer survivors, the message is clear that health professionals should encourage this population to be active and sit less, move more, and move frequently.”

For future research, Cao and colleagues seek to conduct clinical studies to understand the biological mechanisms operating the associations between sedentary behaviors and cancer survival and develop theory-based strategies that can be integrated into cancer survivorship care to decrease sedentary behavior and enhance PA.