Television Viewing Time and the Risk of Colorectal Cancer Mortality among Japanese Population: The JACC Study

Article information

Cancer Res Treat. 2021;53(2):497-505
Publication date (electronic) : 2020 October 27
doi : https://doi.org/10.4143/crt.2020.327
1Public Health, Department of Social Medicine, Osaka University Graduate School of Medicine, Osaka, Japan
2Department of Public Health and Community Medicine Department, Faculty of Medicine, Minia University, Minia, Egypt
3Department of Public Health, Hokkaido University Graduate School of Medicine, Sapporo, Japan
4Research Unit of Advanced Interdisciplinary Care Science, Graduate School of Human Life Science, Osaka City University, Osaka, Japan
Correspondence: Hiroyasu Iso, Public Health, Department of Social Medicine, Osaka University Graduate School of Medicine, Suita-shi, Osaka 565-0871, Japan, Tel: 81-6-6879-3911, Fax: 81-6-6879-3919, E-mail: iso@pbhel.med.osaka-u.ac.jp
*

Study Investigators

Members of the JACC Study Group: Dr. Akiko Tamakoshi (present chairperson of the study group), Hokkaido University Graduate School of Medicine, Dr. Mitsuru Mori, Sapporo Medical University School of Medicine, Dr. Yoshihiro Kaneko, Akita University Graduate School of Medicine, Dr. Ichiro Tsuji, Tohoku University Graduate School of Medicine, Dr. Yosikazu Nakamura, Jichi Medical School, Dr. Hiroyasu Iso, Osaka University School of Medicine, Dr, Kazumasa Yamagishi, Faculty of Medicine, University of Tsukuba, Dr. Haruo Mikami, Chiba Cancer Center, Dr. Michiko Kurosawa, Juntendo University School of Medicine Dr. Yoshiharu Hoshiyama, Yokohama Soei University, Dr. Naohito Tanabe, University of Niigata Prefecture, Dr. Koji Tamakoshi, Nagoya University.

Received 2020 April 17; Accepted 2020 October 26.

Abstract

Purpose

Sedentary behavior attributes to the increased risk of some cancers and all-cause mortality. The evidence is limited for the association between television (TV) viewing time, a major sedentary behavior, and risk of colorectal cancer death. We aimed to examine this association in Japanese population.

Materials and Methods

A prospective cohort study encompassed of 90,834 men and women aged 40–79 years with no prior history of colorectal cancer who completed a self-administered food frequency questionnaire, and provided their TV viewing information. The participants were followed-up from 1988–1990 to the end of 2009. The hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated by the Cox proportional hazard regression for risk of colorectal cancer mortality according to TV viewing time.

Results

During the median 19.1-year follow-up period, we documented 749 (385 men and 364 women) colorectal cancer deaths. The multivariable-adjusted HRs for mortality from colorectal cancer were 1.11 (0.88–1.41) for 1.5 to < 3 hr/day, 1.14 (0.91–1.42) for 3 to < 4.5 hr/day and 1.33 (1.02–1.73) for ≥ 4.5 hr/day in comparison to < 1.5 hr/day TV watching; p-trend=0.038, and that for 1-hour increment in TV viewing time was 1.06 (1.01–1.11). Moreover, the multivariable-adjusted HR (95% CI) of colon cancer for 1-hour increment in TV viewing time was 1.07 (1.02–1.13). Age, body mass index, and level of leisure-physical activity did not show significant effect modifications on the observed associations.

Conclusion

TV viewing time is associated with the increased risk of colorectal cancer mortality among Japanese population, more specifically colon rather than rectal cancer.

Introduction

Colorectal cancer (CRC) is the third most common cancer in men and the second most common cancer in women, with 1.8 million new cases and almost 861,000 deaths in 2018 according to the World Health Organization GLOBOCAN database [1]. CRC mortality has been decreasing since the 1980s in several high-income, east Asian and east European countries, probably because of the improved early detection and treatments [2], but the rates in Japan is still increasing [3], probably due to adopting Westernized lifestyles characterized by higher meat and fat consumption and lower physical activity [4].

Sedentary behavior, such as television (TV) viewing, computer use and driving is known to be associated with poor health outcomes such as diabetes mellitus, cardiovascular disease, some cancers and all-cause mortality [57]. According to the Descriptive Epidemiology of Sitting study, the length of sitting time is approximately 7 hr/day among Japanese people, which is the longest in the world [8]. TV viewing time is a good indicator of leisure-time sedentary behavior in developed countries, including Japan [9].

Although a few previous studies [10,11] in non-Asian countries have examined the association between TV viewing time and the risk of CRC; however, the epidemiological data are limited, and no study has been conducted to investigate the association with the risk of CRC mortality in Asian populations. Therefore, our study aimed to evaluate the association of daily TV viewing time on risk of CRC mortality among Japanese population.

Materials and Methods

1. Study population

The Japan Collaborative Cohort (JACC) Study for Evaluation of Cancer Risks is a large prospective cohort study, the details of this study have been described in previously [12]. Briefly, the JACC study was established in 1988 to 1990 and covered a total of 110,585 individuals (46,395 men and 64,190 women) in 45 areas throughout Japan. Participants’ eligibility was verified by investigators in each area to confirm the participant’s residence in the study area, and that their age was 40–79 years at the baseline. The baseline information was collected by a self-administered questionnaire covering lifestyles and medical histories after obtaining informed consent from participants or local community leaders. Of the total 110,585 participants, we excluded 126 individuals with a medical history of CRC, 19,481 individuals with missing information for daily TV viewing time, and 144 individuals with inappropriate response to the daily TV viewing time (≥ 12 hours) at the baseline survey. This left a total of 90,834 participants (38,130 men and 52,704 women) for the analyses.

2. Follow-up

The follow-up survey for cancer mortality was available in the 45 study areas. The follow-up ended at the end of 1999 in four areas, 2003 in four areas, 2008 in two areas and at the end of 2009 in 35 areas. For data analysis, we obtained a prior approval from the Director-General of the Prime Minister’s Office and/or the Ministry of Health, Labor and Welfare, Japan. As part of death monitoring in each community, investigators conducted a systematic review of the death certificates. The date and cause of death were confirmed and documented once a year or once every 2 years. Participants who moved from their areas during the study period were also verified by the investigator in each area every year or every half a year via reviewing the population-register sheets of the cohort participants. Death from CRC was determined by the 10th revision of the International Statistical Classification of Diseases and Related Health Problems. Tumors with International Classification of Diseases, 10th revision (ICD-10) codes C18, C19, and C20 were classified as CRC. C18 was classified as colon cancer (C18.0–C18.3 for right colon cancer, C18.4 for transverse colon cancer, and C18.5–C18.9 for left |colon cancer), and C19–C20 were classified as rectal cancer as described in a previous study [13].

3. Statistical analysis

This study’s statistical analyses were based on the mortality rates from CRC during the follow-up period from 1988–1990 to the end of 2009. The person-years of follow-up were calculated for all participants from the time of the initial enrollment to the death from CRC or any other cause, the time of moving out from the study area or the end of follow-up, whichever came first. Mean values (standard deviations) and proportions of the baseline characteristics were calculated, and the age-adjusted p-values of trend were calculated using the linear and logistic regressions, respectively. The hazard ratios (HRs) and confidence intervals (CIs) for CRC mortality were calculated using the Cox proportional regression analysis. Information on lifestyle factors and the average daily TV viewing time were obtained in the baseline questionnaire. We classified the daily TV viewing time into four categories: < 1.5 hours, 1.5 to < 3 hours, 3 hours to < 4.5 hours, or ≥ 4.5 hours. Potential confounding factors for adjustment were the baseline’s age (continuous), sex, and residential area in the first model. Additionally, factors associated with the risk of CRC, not only in our data, but also from previous studies, were adjusted in the second model: the family history of CRC in parents or siblings (yes or no), frequency of bowel movement (daily, every 2–3 days, every 4–5 days and every 6 days or less), education level (primary school, junior high school, high school or college and higher), alcohol consumption (never drinkers, ex-drinkers or current drinkers), smoking habits (never smokers, ex-smokers, current smoker of at least 1 cigarette/day but no more than 20 cigarettes/day, or current smoker of more than 20 cigarettes/day), and frequency consumption of beef and pork (almost never, 1–2 times a month, 1–2 times a week, 3–4 times a week, almost every day) were adjusted in the second model. In the fully-adjusted model, we further adjusted for the other proxy variables of the level of physical activity: the body mass index (BMI quartiles), weekly sport hours (seldom or never, 1–2, 3–4, and ≥ 5 hours), and daily walking time in minutes (seldom or never, < 30 minutes, 30–59 minutes, or ≥ 60 minutes). Missing values for these covariates were treated as additional missing categories and their dummy variable indicators were included into the model. p-value for trend across the TV viewing time categories was calculated by adding the median value of TV viewing time into each category in the model. In sensitivity analyses, we stratified by the median age, BMI (< or ≥ 25 kg/m2), and levels of leisure-time physical activity (low or high, where persons with high level of leisure-time physical activity included those who walk for 1 hour or more per day and/or practice sports for 5 hours or more per week, while those with low level of leisure-time physical activity included persons who walk for less than 1 hour per day and practice sports for less than 5 hours per week). We also examined the associations after removing the first 3-year of follow-up for all study participants to confirm whether TV viewing time was associated with the later onset of CRC with avoiding immortal bias time [14]. We used the SAS ver. 9.4 software (SAS Institute Inc, Cary, NC) in all statistical analyses. Two-tailed p-values of < 0.05 were considered statistically significant.

Results

Table 1 shows the baseline characteristics of the participants according to TV viewing time. The proportion of participants spent 4.5 hours or longer daily on TV watching was 13.3%. Compared with participants with TV viewing time < 1.5 hr/day, participants in longer TV viewing time categories tended to be older, with higher BMI and less educated, and consumed less beef and pork.

Baseline characteristics of participants according to television viewing time

Among the 90,834 participants (38,130 men and 52,704 women) aged 40–79 years at the baseline examination and within the median 19.1-year follow-up period, we identified 749 CRC deaths (385 in men and 364 in women). Table 2 shows the HRs for mortality from the total CRC and anatomical sub-sites of CRC according to TV viewing time categories as well as for 1-hour increment of TV viewing time in minimal-and fully-adjusted models. The multivariable HRs (95% CIs) of mortality from CRC were 1.11 (0.88–1.41) for 1.5 to < 3 hours, 1.14 (0.91–1.42) for 3 to < 4.5 hours, and 1.33 (1.02–1.73) for ≥ 4.5 hours of daily TV viewing; p-trend=0.038, and 1-hour increment of TV viewing time was associated with a HR 1.06 (1.01–1.11). In addition, the multivariable HR (95% CI) of colon cancer mortality in highest compared with the lowest category of TV viewing time was 1.43 (1.04–1.96); p for trend=0.049. The multivariable HRs (95% CIs) in highest compared with the lowest category of TV viewing time were 1.42 (0.98–2.07, p-trend=0.131) for left colon cancer, 3.55 (0.72–17.46, p-trend=0.182) for transverse colon cancer, and 1.16 (0.60–2.24, p-trend=0.465) for right colon cancer. Further adjustment for the perceived mental stress, sleep hours, history of diabetes, and intakes of vegetables and fruit into the model did not change the associations (data not shown). Sex-specific results were similar and no significant interaction by sex could be detected (p > 0.1); the HRs of CRC mortality per 1-hour increment in TV viewing time were 1.07 (1.00–1.15) in men and 1.06 (1.00–1.13) in women (data not shown).

Hazard ratios (95% confidence intervals) of colorectal cancer mortality according to television viewing time

Table 3 shows the stratification analyses by the median age, BMI cutoff level of overweight, and level of leisure-time physical activity. The p-values for interactions between TV viewing time and all the stratifying variables were > 0.1 for all cancers, and the increased risk of CRC mortality with longer TV viewing time did not largely differ for the younger and older participants. However, the positive association between longer TV viewing time and risk of CRC mortality was more robust for persons with BMI < 25 kg/m2, and for persons with high level of leisure-time physical activity; HRs per 1-hour increment in TV viewing time were 1.07 (1.02–1.13), and 1.07 (1.00–1.15), respectively than for those with BMI ≥ 25 kg/m2 and for persons with low level of leisure-time physical activity; the respective HRs were 1.02 (0.92–1.21), and 1.04 (0.97–1.10).

Multivariable hazard ratios (95% confidence intervals)a) of colorectal cancer mortality, stratified by median age, BMI and level of physical activity according to television viewing time

We compared the participants’ characteristics for those included in the study and those who were excluded due to missing answers of TV viewing time in the S1 Table. There were no differences in the mean age, BMI, or sleep duration, nor in the frequency of bowel movement or sports activity habits. However, the excluded participants were less likely to have a family history of CRC, less likely to walk for ≥ 30 minutes per day, less likely to be educated to a college or higher levels, but more likely to smoke and to drink alcohol and consumed more beef and pork than those included in our analyses.

After excluding the first 3-year of the follow-up, during which there were 42 CRC deaths (42 colon cancer and 0 rectal cancer), the associations between the TV viewing time and risk of mortality from CRC and colon cancer did not change materially in both the categorical and continuous analyses. Actually, it was slightly augmented, especially for the association with colon cancer mortality (S2 Table).

Discussion

In this large prospective study of Japanese men and women, we found that the longer average daily TV viewing time was associated with the increased risk of CRC mortality. The 1-hour increment of TV viewing time was associated with almost similar ~6% higher risk of CRC mortality and ~7% higher risk of colon cancer deaths. The exclusion of the initial 3 years of follow-up did not alter the observed associations. No significant effect modifications by age, BMI, or level of leisure-time physical activity could be detected; however, the findings suggested robust decline in the risk of CRC mortality by reducing the TV watching time among lean participants with BMI < 25 kg/m2 and persons who frequently walk and/or practice sports.

Our findings were consistent with previous studies [15,16]; the UK Biobank cohort study of 430,584 men and women with a median follow-up time of 5.6 years showed that TV viewing time was associated with increased risk of CRC; the multivariable HR (95% CIs) was 1.26 (1.04–1.53) for > 5 hr/day versus ≤ 1 hr/day, p-trend=0.01 [15]. In a meta-analysis [16] of 47,84,339 participants from 28 cohort studies with a total of 46,071 incident cases of CRC, the summary relative risk (RR) of CRC per 2 hours increment of TV viewing time was 1.07 (95% CI, 1.05 to 1.10; p < 0.001). The TV viewing time was not only positively associated with the risk of developing CRC, but also was inversely associated with the survival among CRC patients in two American cohorts [17,18]. However, one study showed the association with survival was confined to pre-diagnostic (HR, 2.13 [1.31–3.45] for 21 hr/wk vs. 7 hr/wk) but not post-diagnostic TV viewing hours (HR, 1.45 [0.73–2.87] for 21 hr/wk vs. 7 hr/wk] [17], and the other showed the opposite; RRs were 1.33 (0.96–1.84) for ≥ 6 hr/day compared to < 3 hr/day pre-diagnosis leisure sitting time, and 1.62 (1.07–2.44) for ≥ 6 hr/day compared to < 3 hr/day post-diagnosis leisure sitting time [18].

As for the anatomical site of CRC, TV viewing time was associated more strongly with risk of mortality from colon cancer rather than rectal cancer, which was consistent with a finding from the previous studies [11,15] where sedentary behaviors were associated with higher risk of colon cancer but not rectal cancer. For example, in 430,584 participants of the UK Biobank study, TV viewing time was associated with higher risk of colon cancer but not rectal cancer; HRs for ≥ 5 hr/day versus ≤ 1 hr/day were 1.32 (1.04–1.68) and 1.13 (0.79–1.61), respectively [15]. However, another possible explanation for the non-significant association between TV viewing time and risk of mortality from rectal cancer in our study may be due to the low statistical power to detect the association. TV viewing time tended to be positively associated with risk of mortality from left colon cancer and transverse colon cancer, but we could not find an association with risk of mortality from right colon cancer. This also could be attributed to the low power to detect the association. However, the histopathologic, epidemiologic, molecular, and genetic perspectives of right and left colon cancers were shown to vary greatly [19]; therefore, further studies to explore the possible differential associations between sedentary behaviors and risk of right, transverse and left colon cancers, and to propose biological mechanisms are needed.

It has been indicated that age, obesity besides to the physical activity are important factors in the pathogeneses of CRC [4,20]. We not only controlled for these factors in our model, but in order to test the independent association of TV viewing time with risk of CRC mortality, we also stratified our analyses by the median age of our participants (58 years), by the BMI cut off level of obesity (25 kg/m2), and by the level of leisure-time physical activity indicated by hours of sports and walking activities. We found no significant effect modifications of these factors, and the positive association between TV viewing time and risk of CRC mortality was evident in both younger and older persons.

The level of leisure-time physical activity was suggested as an important factor in the pathogenies of CRC [18], and obesity could be an intermediate outcome between sedentary lifestyles such as long TV watching time and the risk of CRC mortality [4].

However, the stratified analyses by leisure-physical activity and BMI in our study suggested that the longer TV viewing duration was associated with risks of CRC and colon cancer mortality in persons with high level of leisure-physical activity and those with BMI < 25 kg/m2 rather than persons with low level of leisure-physical activity and those with higher BMI. Accordingly, reducing the time in front of TV could be associated with the lower risk of CRC mortality in lean and more physically active, but not overweight and less physically active Japanese men and women. For the overweight and less physically active persons, reducing the TV watching time seems not enough to counteract the increased risk of CRC, or in another expression, longer TV viewing time added no more significant risk of CRC to those who are less physically active or overweight.

It is worth pointing here to the low prevalence of obesity in Japanese (3.9%) [21]; persons with BMI ≥ 30 kg/m2 in our study composed only 1.6% of the total study participants. Another hypothesis could explain the association between longer TV viewing time and CRC mortality, especially in lean persons is that sedentary behavior may also be associated enhanced systematic inflammation independent of obesity [22]. C-reactive protein, a marker of inflammation, was positively associated with sedentary time [22] and risk of CRC mortality [23]. An 8-year follow-up study [23] of 368 CRC patients showed that the plasma levels of C-reactive protein was positively associated with the risk of CRC mortality; the multivariable HRs (95% CIs) of CRC mortality was 1.80 (1.07–3.04) for highest versus lowest quintiles of C-reactive protein. On the other hand, previous studies suggested that obesity may promote cancer progression through a number of pathways including the increased levels of insulin-like growth factors (IGFs) and cortisol and the reduced immune function [24]. In the metabolic syndrome, diabetes-related visceral obesity is characterized by high serum levels of IGFs that may affect tumor aggressiveness [25,26] by promoting tumor cell proliferation and angiogenesis [27]. Moreover, IGFs binding protein levels were inversely associated with the risk of CRC mortality in American experimental [28] and cohort studies [29]. Last, leisure-time sedentary behavior such as watching TV are usually associated with unhealthy dietary behaviors [30], such as heavily burnt meat intake, higher consumption of sugar sweetened beverages, and less consumption of vegetables, which were related to the development and progression of CRC [31]. We adjusted for these potential confounders in the multivariable model and found no material change in the results.

The strengths of this study were its community-based prospective design and the large cohort sample size with high response rate and perfect follow-up [12]. Errors of recall should have been non-differential between the CRC cases and non-cases because we assessed TV viewing time before the diagnosis of CRC, and we also excluded the first 5 years of follow-up. Moreover, the information on potential confounding factors of CRC was collected at baseline and adjusted for as much as possible.

Our study also has several limitations. First, the information on average TV viewing time was collected only at baseline and was not updated during the study period. Misclassifications might have been included in the results if the participants had changed their lifestyle. However, such error would have occurred at random that might have reduced the estimated HRs toward the null. Second, the average TV viewing time was self-reported which may have led to some misclassifications. However, a previous review [32] reported that the reliability of the self-reported time spent on TV watching was consistently moderate to high (r=0.69–0.83, p < 0.001). Third, residual confounding cannot be eliminated; for example, we do not have data on CRC screening or the time or the stage of cancer at diagnosis in our cohort study which are important factors associated with CRC mortality [20,33]. Last, although the age and BMI of the studied participants did not differ than those of the excluded ones; however, those excluded due to missing data on the TV viewing time carried more risky profile such as less walking activity, higher prevalence of smokers and alcohol drinkers which could infer some sort of unavoidable selection bias.

In conclusion, our findings provide further evidence that TV viewing time associate with increased risk of CRC mortality, more specifically mortality from colon cancer, among Japanese men and women.

Electronic Supplementary Material

Supplementary materials are available at Cancer Research and Treatment website (https://www.e-crt.org).

Notes

Ethical Statement

This cohort study was sponsored by the Ministry of Education, Sport, and Science and approved by the ethical Review Board of Hokkaido University and Osaka University, with the approval number 14285-6.

Author Contributions

Conceived and designed the analysis: Li Y, Iso H.

Collected the data: JACC Study Group.

Contributed data or analysis tools: Tamakoshi A, Iso H, Cui R.

Performed the analysis: Li Y, Eshak ES.

Wrote the paper: Li Y.

Revised paper: Iso H, Eshak ES, Cui R, Shirai K, Liu K, Ikehara S, Tamakoshi A, Ukawa S.

Conflicts of Interest

Conflicts of interest relevant to this article was not reported.

Acknowledgements

The authors thank all staff members involved in this study for their valuable help in conducting the baseline survey and follow-up.

This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) (Monbusho); Grants-in-Aid for Scientific Research on Priority Areas of Cancer; and Grants-in-Aid for Scientific Research on Priority Areas of Cancer Epidemiology from MEXT (MonbuKagaku-sho) (Nos. 61010076, 62010074, 63010074, 1010068, 2151065, 3151064, 4151063, 5151069, 6279102, 11181101, 17015022, 18014011, 20014026, 20390156, 26293138 and 16H06277).

This research was also supported by a grant-in-aid from the Ministry of Health, Labour and Welfare, Health and Labor Sciences research grants, Japan (Research on Health Services: H17-Kenkou-007; Comprehensive Research on Cardiovascular Disease and Life-Related Disease: H18-Junkankitou[Seishuu]-Ippan-012; Comprehensive Research on Cardiovascular Disease and Life-Related Disease: H19-Junkankitou [Seishuu]-Ippan-012; Comprehensive Research on Cardiovascular and Life-Style Related Diseases: H20-Junkankitou [Seishuu]-Ippan-013; Comprehensive Research on Cardiovascular and Life–Style Related Diseases: H23-Junkankitou [Seishuu]-Ippan-005); an Intramural Research Fund (22-4-5) for Cardiovascular Diseases of National Cerebral and Cardiovascular Center; Comprehensive Research on Cardiovascular and Life-Style Related Diseases (H26-Junkankitou [Seisaku]-Ippan-001) and H29-Junkankitou [Seishuu]-Ippan-003) and 20FA1002.

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Article information Continued

Table 1

Baseline characteristics of participants according to television viewing time

Characteristic Television viewing time (hr/day)
< 1.5 1.5 to < 3 3 to < 4.5 ≥ 4.5 p for trend
No. at risk 15,386 27,430 35,977 12,041
Age, mean±SD (yr) 56±10 56±10 58±10 62±9 < 0.001
Men (%) 41.5 45.0 42.9 33.2 < 0.001
BMI, mean±SD (kg/m2) 22.6±2.9 22.7±2.9 22.9±3.0 23.0±3.3 < 0.001
BMI ≥ 25 kg/m2 (%) 17.3 18.4 20.8 22.6 < 0.001
BMI ≥ 30 kg/m2 (%) 1.3 1.3 1.7 2.6 < 0.001
Family history of colorectal cancer (%) 2.3 2.3 2.2 2.0 0.13
Exercise ≥ 3 hr/wk (%) 10.9 12.2 12.1 12.6 < 0.001
Walking ≥ 30 min/day (%) 70.9 71.9 71.2 65.2 < 0.001
College or higher education (%) 14.5 12.0 9.7 7.9 < 0.001
Current smokers (%) 23.3 26.9 27.7 25.2 < 0.001
Current drinkers (%) 45.7 48.3 45.1 37.6 < 0.001
Consumption of beef ≥ 3 times/wk (%) 10.4 9.4 9.3 9.1 < 0.001
Consumption of pork ≥ 3 times/wk (%) 21.7 21.5 20.6 17.3 < 0.001

p for trend was adjusted for age. BMI, body mass index; SD, standard deviation.

Table 2

Hazard ratios (95% confidence intervals) of colorectal cancer mortality according to television viewing time

Television viewing time (hr/day)
< 1.5 1.5 to < 3 3 to < 4.5 ≥ 4.5 p for trend 1-Hour increment television viewing time
Person-years 256,146 454,237 577,700 172,018
Colorectal cancer
 No. of cases 102 212 308 127
 Model 1 1.00 1.12 (0.88–1.41) 1.15 (0.92–1.44) 1.36 (1.04–1.77) 0.022 1.07 (1.02–1.11)
 Model 2 1.00 1.12 (0.88–1.41) 1.15 (0.91–1.43) 1.34 (1.03–1.74) 0.031 1.06 (1.02–1.11)
 Model 3 1.00 1.11 (0.88–1.41) 1.14 (0.91–1.42) 1.33 (1.02–1.73) 0.038 1.06 (1.01–1.11)
Colon cancer
 No. of cases 67 152 216 96
 Model 1 1.00 1.22 (0.92–1.63) 1.21 (0.92–1.60) 1.47 (1.07–2.01) 0.026 1.08 (1.02–1.13)
 Model 2 1.00 1.24 (0.93–1.65) 1.22 (0.93–1.61) 1.45 (1.06–2.00) 0.035 1.07 (1.02–1.13)
 Model 3 1.00 1.22 (0.92–1.63) 1.20 (0.91–1.58) 1.43 (1.04–1.96) 0.049 1.07 (1.02–1.13)
Right colon cancer
 No. of cases 18 35 63 19
 Model 1 1.00 1.05 (0.60–1.85) 1.33 (0.79–2.26) 1.12 (0.58–2.14) 0.554 1.06 (0.96–1.18)
 Model 2 1.00 1.07 (0.60–1.88) 1.39 (0.82–2.35) 1.19 (0.62–2.28) 0.422 1.08 (0.97–1.20)
 Model 3 1.00 1.05 (0.60–1.86) 1.36 (0.81–2.31) 1.16 (0.60–2.24) 0.465 1.08 (0.97–1.20)
Transverse colon cancer
 No. of cases 2 10 14 7
 Model 1 1.00 2.72 (0.60–12.40) 2.67 (0.61–11.74) 3.59 (0.74–17.46) 0.164 1.17 (0.97–1.42)
 Model 2 1.00 2.78 (0.61–12.71) 2.69 (0.61–11.90) 3.60 (0.74–17.65) 0.174 1.18 (0.97–1.43)
 Model 3 1.00 2.74 (0.60–12.56) 2.67 (0.60–11.80) 3.55 (0.72–17.46) 0.182 1.19 (0.97–1.44)
Left colon cancer
 No. of cases 47 107 139 70
 Model 1 1.00 1.22 (0.87–1.72) 1.11 (0.79–1.54) 1.51 (1.04–2.19) 0.057 1.07 (1.01–1.14)
 Model 2 1.00 1.23 (0.87–1.74) 1.10 (0.79–1.53) 1.45 (1.00–2.11) 0.102 1.06 (1.00–1.13)
 Model 3 1.00 1.23 (0.87–1.73) 1.09 (0.78–1.52) 1.42 (0.98–2.07) 0.131 1.06 (0.99–1.13)
Rectal cancer
 No. of cases 35 60 92 31
 Model 1 1.00 0.91 (0.60–1.39) 1.04 (0.70–1.53) 1.13 (0.69–1.84) 0.451 1.03 (0.94–1.13)
 Model 2 1.00 0.89 (0.59–1.35) 1.01 (0.68–1.49) 1.11 (0.68–1.81) 0.492 1.03 (0.94–1.13)
 Model 3 1.00 0.90 (0.59–1.36) 1.01 (0.69–1.50) 1.13 (0.69–1.85) 0.450 1.03 (0.94–1.13)

Model 1: Adjusted for age, sex and areas; Model 2: Further adjusted for smoking, drinking, family history of colorectal cancer, education level, frequency of bowel movement, frequency consumption of beef and pork; Model 3: Further adjusted for hours of sport, minutes of waking and body mass index.

Table 3

Multivariable hazard ratios (95% confidence intervals)a) of colorectal cancer mortality, stratified by median age, BMI and level of physical activity according to television viewing time

Television viewing time (hr/day)
< 1.5 1.5 to < 3 3 to < 4.5 ≥ 4.5 p for trend 1-Hour increment television viewing time
Age < 58 yr
 Person-years 158,912 266,818 293,830 59,339
 Colorectal cancer
  No. of cases 31 63 85 21
  HR (95% CI) 1.00 1.13 (0.73–1.73) 1.32 (0.87–2.00) 1.61 (0.92–2.83) 0.057 1.08 (0.98–1.20)
 Colon cancer
  No. of cases 16 42 54 13
  HR (95% CI) 1.00 1.48 (0.83–2.64) 1.67 (0.95–2.93) 1.87 (0.89–3.94) 0.070 1.11 (0.98–1.26)
 Rectal cancer
  No. of cases 15 21 31 8
  HR (95% CI) 1.00 0.74 (0.38–1.44) 0.95 (0.51–1.78) 1.35 (0.56–3.24) 0.402 1.03 (0.86–1.24)
Age ≥ 58 yr
 Person-years 97,234 187,419 283,870 112,679
 Colorectal cancer
  No. of cases 71 149 223 106
  HR (95% CI) 1.00 1.10 (0.83–1.46) 1.06 (0.81–1.39) 1.24 (0.91–1.68) 0.204 1.05 (1.00–1.11)
 Colon cancer
  No. of cases 51 110 162 83
  HR (95% CI) 1.00 1.14 (0.82–1.59) 1.08 (0.78–1.48) 1.30 (0.92–1.86) 0.180 1.06 (1.01–1.13)
 Rectal cancer
  No. of cases 20 39 61 23
  HR (95% CI) 1.00 0.99 (0.58–1.70) 1.03(0.62–1.71) 1.06 (0.58–1.70) 0.801 1.03 (0.93–1.14)
  pinteraction > 0.1
BMI < 25 kg/m2
 Person-years 197,109 349,028 426,867 119,891
 Colorectal cancer
  No. of cases 73 155 227 89
  HR (95% CI) 1.00 1.12 (0.84–1.47) 1.18 (0.91–1.54) 1.39 (1.01–1.90) 0.034 1.07 (1.02–1.13)
 Colon cancer
  No. of cases 49 108 159 65
  HR (95% CI) 1.00 1.16 (0.83–1.63) 1.21 (0.88–1.67) 1.39 (0.96–2.03) 0.090 1.08 (1.02–1.15)
 Rectal cancer
  No. of cases 24 47 68 24
  HR (95% CI) 1.00 1.03 (0.63–1.69) 1.13 (0.71–1.81) 1.40 (0.78–2.49) 0.206 1.05 (0.95–1.17)
BMI ≥ 25 kg/m2
 Person-years 45,035 85,783 123,662 41,900
 Colorectal cancer
  No. of cases 18 42 62 28
  HR (95% CI) 1.00 1.15 (0.66–2.00) 1.09 (0.64–1.85) 1.16 (0.63–2.12) 0.751 1.02 (0.92–1.21)
 Colon cancer
  No. of cases 10 33 43 22
  HR (95% CI) 1.00 1.67 (0.82–3.39) 1.38 (0.69–2.76) 1.62 (0.76–3.47) 0.475 1.03 (0.92–1.16)
 Rectal cancer
  No. of cases 8 9 19 6
  HR (95% CI) 1.00 0.52 (0.20–1.35) 0.72 (0.31–1.65) 0.56 (0.19–1.65) 0.520 0.95 (0.78–1.17)
  pinteraction > 0.1
High leisure-time physical activity
 Person-years 126,529 224,779 276,834 71,163
 Colorectal cancer
  No. of cases 50 110 148 57
  HR (95% CI) 1.00 1.19 (0.85–1.66) 1.17 (0.85–1.62) 1.53 (1.04–2.24) 0.045 1.07 (1.00–1.15)
 Colon cancer
  No. of cases 31 81 104 42
  HR (95% CI) 1.00 1.44 (0.95–2.17) 1.33 (0.89–1.99) 1.72 (1.08–2.76) 0.059 1.09 (1.01–1.18)
 Rectal cancer
  No. of cases 19 29 44 15
  HR (95% CI) 1.00 0.79 (0.44–1.40) 0.91 (0.53–1.57) 1.20 (0.60–2.39) 0.456 1.03 (0.90–1.18)
Low leisure-time physical activity
 Person-years 122,794 221,136 289,445 96,141
 Colorectal cancer
  No. of cases 49 96 153 64
  HR (95% CI) 1.00 1.00 (0.71–1.41) 1.08 (0.78–1.49) 1.10 (0.75–1.61) 0.515 1.04 (0.97–1.10)
 Colon cancer
  No. of cases 34 69 105 49
  HR (95% CI) 1.00 1.04 (0.69–1.57) 1.05 (0.71–1.55) 1.13 (0.72–1.77) 0.575 1.04 (0.97–1.12)
 Rectal cancer
  No. of cases 15 27 48 15
  HR (95% CI) 1.00 0.91 (0.48–1.71) 1.15 (0.64–2.06) 1.02 (0.49–2.11) 0.727 1.03 (0.91–1.16)
  pinteraction > 0.1

p for interaction with age, BMI and level of physical activity were > 0.1 for all cancers in Table 3. BMI, body mass index; CI, confidence interval; HR, hazard ratio

a)

Multivariable adjustments are the same as shown in Model 3 of Table 2, except for the stratifying variable.