Background
Over 1 million cancer survivors are alive in Korea in 2016 [
1] and cancer has been the leading cause of death in Korea since 1983 and is one of the most serious diseases [
2]. Overall, the 5-year relative survival rate for people diagnosed with cancer between 2012 and 2016 was 70.6%, which represents an improved survival rate as compared with 41.2% for people diagnosed between 1993 and 1995 [
1]. Cancer survivors report significantly lower levels of health-related quality of life (QoL) than non-cancer population [
3,
4]. Cancer diagnosis is a major stressor resulting in considerable psychological suffering [
5‐
7]. During and after cancer treatments, cancer patients frequently experience diverse physical and psychological symptoms including anxiety, fear, fatigue, pain, depression as well as decreases in overall functions [
8‐
10]. Additionally, previous studies in diverse populations indicate that suicide is approximately twice as prevalent among patients with cancer compared with the general population [
11‐
13].
Well-known way to improve mental health and QoL among cancer patients is through exercise and physical activity (PA). A systemic review reported that PA interventions significantly improved QoL in cancer survivors [
14,
15]. Additionally, PA participation has been associated with reduced cancer-specific and all-cause mortality in breast and colorectal cancer survivors [
16,
17]. Despite the growing evidence showing the benefits of exercise and PA on physical function, psychological health and prognosis and the safety of participating in exercise for cancer patients, many cancer patients still remain physically inactive [
16,
18,
19]. Studies reported that 30–47% of cancer survivors in the United States met the American College of Sports Medicine (ACSM)‘s exercise recommendation [
20,
21], while only 25.2% of Korean colorectal cancer survivors met the ACSM’s exercise recommendations that is significantly lower than the percentage among the non-cancer population [
22]. Although the benefit of PA is well known among cancer survivors, there is limited data on the relationship between PA participation and QoL among Korean cancer survivors. Therefore, the purpose of this study was to investigate the association between the level of self-reported PA and QoL in breast and colorectal cancer survivors in Korea.
Discussion
This cross-sectional study was to examine whether the amount of self-reported PA is associated with QoL among Korean breast and colorectal cancer survivors. As hypothesized, higher amount of moderate to vigorous and total PA (sum of light, moderate, and vigorous PA) were significantly associated with higher QoL while no association between the amount of light PA and any of the QoL variables was shown. These associations were supported when our participants were divided into quartiles and their QoL outcomes were compared across quartiles. Compared with participants in the 1st quartile (the least active), participants in the 4th quartile had 11.8 point (65.8 vs. 77.6 point) higher scores in global QoL, clinically meaningful moderate differences [
29] .
Findings from the current study are supported by previous studies reported that moderate to vigorous PA is associated with health-related QoL among colorectal cancer survivors [
30,
31]. Moreover, accumulating evidence suggests that participation of PA contributes to improved QoL through positive changes in physical, psychological, social and spiritual factors [
32,
33]. What is unique and interesting about our finding is that light PA was not associated with any of QoL variables. We have previously demonstrated that under cancer treatment, moderate to vigorous PA participation decreases while light PA increases among Korean colorectal cancer survivors [
22]. Current ACSM PA recommendations for cancer survivors focus on accumulating adequate level of moderate to vigorous PA level (overall level of weekly activity of 150 min of moderate-intensity exercise or 75 min of vigorous-intensity exercise or an equivalent combination). Cochrane Review revealed that PA at moderate to vigorous intensity provides greater health benefits than low-intensity PA [
34]. Interestingly, our study found that significantly higher QoL score in the 4th quartile of PA group compared with 1st quartile of PA group. Participants in the 4th quartile may have been only group which met the ACSM guidelines for cancer survivors (mean of moderate to vigorous PA Q1: 5.5 min/wk., Q2: 31.4 min/wk., Q3: 109.1 min/wk., Q4: 368.9 min/wk) but we still observed better QoL with higher PA in the second and third quartiles. Therefore, it is important to encourage moderate to vigorous PA among cancer survivors to improve QoL.
In order to better understand our data, we conducted subgroup analyses by potential effect modifiers and found that meeting the ACSM PA guideline was more closely associated with better global QoL among participants whose cancer stage was greater than stage II. Normally, cancer patients with stage 0-II undergo surgery and some receive additional therapy but cancer patients above stage II most often receive radiation and/or chemotherapy in addition to surgery. Patients undergoing radiation and chemotherapy treatment experience decline in their perceived QoL during treatment. This finding suggests that cancer survivors above stage II could benefit more from participating PA to improve QoL.
Given the importance of regular PA for disease prevention and health promotion [
35], the low number of participants meeting the ACSM PA guideline is of concern. Our study found only 27.7% of cancer survivors met the exercise recommendations of the ACSM. Consistent with our findings, Chung et al. reported that 25.2% of Korean colorectal cancer patients met the ACSM PA guideline [
22]. However, other studies have reported higher percentage of cancer survivors who met the ACSM PA guideline in other populations. Irwin et al., [
18] reported 32% of breast cancer survivors and Blanchard et al. reported, [
36] 30–47% of cancer survivors met the ACSM PA guideline. Recently, we have reported that oncologists’ PA recommendation to their cancer survivors when given with pedometer and exercise diary significantly increased cancer survivors’ PA participation [
37]. Therefore, oncologists should team up with exercise specialists to provide proper and effective strategies to increase PA level of cancer survivors.
One of the limitations of our study is the nature of cross-sectional study that we cannot draw cause and effect conclusion. We may not be able to say higher PA level resulted in improved QoL since we cannot eliminate the possibility that those with higher QoL might have been in better physical condition which make them possible to participate in moderate to vigorous PA. To reduce this concern, we further analyzed our data after controlling for important sociodemographic and treatment related confounders and still found significant associations between the amount of PA and QoL. Furthermore, our multiple regression analysis also showed that only PA was a significant predictor of global QoL, suggesting the importance of PA. However, we suggest the need to further investigate the effect of moderate to vigorous exercise on QoL in a large randomized controlled trial among Korean cancer survivors. There are other limitations in our study. The reliance on self-report rather than objective measure of exercise behaviors may lead to imprecise measurements. However, use of accelerometer may also have limitation that predefined moderate to vigorous PA measured by accelerometer may not truly reflect PA levels of cancer survivors [
38]. Moreover, our study sample was single clinic-based rather than population-based. Our study participants (particularly colorectal cancer patients) were younger than the general Korean cancer patients [
39] which may reduce the generalizability of the findings to all breast and colorectal cancer survivors.
In conclusion, we found that increased moderate to vigorous PA participation was associated with higher QoL in breast and colorectal cancer survivors in Korea while no association was found between light PA and QoL. When cancer survivors can safely participate in PA with higher intensity, moderate PA should be recommended to improve QoL.
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