Ho, JWC

Lam, TH

Yuen, ST

Hong Kong Medical Journal

HKU Scholars Hub

TitleA case-control study on environmental and familial risk factorsfor colorectal cancer in Hong Kong: physical activity reducescolorectal cancer riskAuthor(s) Ho, JWC; Yuen, ST; Lam, THCitation Hong Kong Medical Journal, 2006, v. 12 n. 2 Supp 1, p. 8-10Issued Date 2006URL http://hdl.handle.net/10722/45483Rights Creative Commons: Attribution 3.0 Hong Kong License8      Hong Kong Med J Vol 12 No 2 Supplement 1 April 2006RESEARCH DISSEMINATION REPORT—CANCERHong Kong Med J 2006;12 (Suppl 1):S8-10A case-control study on environmentaland familial risk factors for colorectalcancer in Hong Kong: physical activityreduces colorectal cancer risk○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○Queen Mary Hospital:Department of SurgeryJWC HoDepartment of PathologyST YuenDepartment of Community Medicine, TheUniversity of Hong KongTH LamHSRF project number: 721019(2)Principal applicant and corresponding author:JWC HoDivision of Colorectal SurgeryDepartment of SurgeryUniversity of Hong Kong Medical CentreQueen Mary Hospital102 Pokfulam RoadHong Kong SAR, ChinaTel: (852) 2855 4762Fax: (852) 2872 8425JWC Ho  ST Yuen  TH Lam  IntroductionColorectal cancer is the most commonly investigated malignancy in relation tophysical activity. Three previous studies on physical activity and colorectalcancer in different Chinese populations showed positive association betweeneither occupation-related or leisure-time activity level with colon cancer. Noconvincing association could be found for rectal cancer.In Hong Kong, like most developed countries, physical inactivity is theprevalent lifestyle. In one local study,1 59% of subjects did not exercise overa 1-month period; and less than 30% reported exercise for a duration of morethan 30 minutes at least twice a week. The relationship of such sedentary life-style with colorectal cancer, the second commonest malignancy in Hong Kong,was unknown till now.MethodsThis report describes the results of a hospital-based case-control studyconducted in three Hospital Authority hospitals from April 1998 to March 2000.We assessed, in a comprehensive manner using a validated questionnaire,the association of colorectal cancer with various types of physical activity,including occupation-related activity, leisure-time exercise, and overall activitypattern. Among 1120 and 960 subjects identified for the case and control groups,we recruited and interviewed 822 cases and 926 controls, respectively. Thissample size was adequate for detecting an odds ratio of 1.8 for risk factors ofuncommon (5%) exposure and 1.4 for risk factors of common (one third)exposure. The results were adjusted for potential confounders including energyand nutrient intakes, body build, smoking and drinking habits as well ashereditary predisposition.ResultsAssociation of overall activity pattern with colorectal cancer risk 2years prior to interviewCases slept for significantly longer duration than controls (mean weekly duration:56.9±13.0 hours for cases and 54.9±13.2 hours for controls, P<0.005).Compared with those at the lowest tertile (<49.0 hours), subjects who slept formore than 59.5 hours per week had significantly increased colon and rectalcancer risk before and after adjustment of confounders (ORadjusted colon cancers=1.45;95% CI, 1.07-1.98; ORadjusted rectal cancers=1.82; 95% CI, 1.29-2.25).For the weekly duration spent in moderate to very active physical activities,those at the highest tertile (>38.5 hours) had a significantly lower risk of colorectalcancer than those at the lowest tertile (<29.2 hours) before and after adjustmentfor confounders (ORadjusted=9.75; 95% CI, 0.58-0.97) [Fig 1].Increasing intensity of weekly physical activity expressed as metabolic equiva-lent tasks (MET) hours per week resulted in progressive reduction in the risk ofKey Messages1. The public should be educatedabout the health hazards associ-ated with a sedentary lifestyleand the benefits of increasedphysical activity.2. Health care policies aiming atincreasing the physical activityof the general population shouldinclude:a. Improvement in workplacepolicy and design to increaseactivity of sedentary workersby encouraging the use ofstairs and incorporatingexercise facilities close tooffices.b. Increased accessibility ofsports and recreationalfacilities to the public andincreased emphasis onphysical exercise lessons inthe school curriculum.Hong Kong Med J Vol 12 No 2 Supplement 1 April 2006      9Physical activity reduces colorectal cancer riskcolorectal cancer in a dose-response manner (ORadjusted midtertile=0.91; 95% CI, 0.71-1.16 and ORadjusted highest tertile=0.67;95% CI, 0.52-0.87, P for trend 0.003). The results were thesame for the subsites of colon and rectal cancers (P for trend0.005 and 0.023, respectively) [Fig 2].Lifelong job-related activity level and its associationwith colorectal cancerThere was no difference in the total working duration, therate of retirement, and the duration of retirement betweencases and controls.Compared with sedentary jobs, those with jobs ofmedium and heavy activity level had significantly reducedrisk of colorectal cancer, which persisted even afteradjustment for potential confounders (P for trend 0.002)[Fig 3]. For rectal cancer, subjects with medium to heavyjobs had a significantly reduced risk when compared withthose whose work activity was sedentary to light (ORadjusted=0.76; 95% CI, 0.58-0.99). When the data were reanalysedafter exclusion of retired subjects, the same results wereobtained (data not shown).Association of leisure-time activity level withcolorectal cancer risk 2 years prior to interviewAt the reference date, 380 (46.7%) cases and 450 (49.0%)controls participated in some form of physical exercisein their leisure time (P>0.05). Only 5.0% of cases and9.5% of controls exercised most days of the week. Thisreluctance in exercising agreed with previous localstudies.1-3 Moreover, the frequency of exercise in ourcontrols, as stratified according to sex and age, was verysimilar to those from the subjects of the Hong KongCardiovascular Risk Factor Prevalence Study.1 Thisfinding suggested that the activity level of our hospitalcontrols was very similar to that of the general populationand information bias was minimal. Those who exercisedat least 28 times a month had a significantly reducedrisk of colorectal cancers than those who exercisedless often (ORadjusted=0.59; 95% CI, 0.39-0.89). Onsubsite analysis, the adjusted results remained significantfor colon cancers (ORadjusted=0.53; 95% CI, 0.31-0.89).Combined assessment of all three aspects of activitylevelSubjects were reclassified into five groups depending onthe number of target activity levels achieved. Compared withsubjects who achieved none of the target activity levels, thosewho achieved at least two activity levels had significantlyreduced colon and rectal cancer risk. Moreover, the risk ofcolon and rectal cancer reduced with increasing combinedactivity level in a dose-response manner (P for trend 0.000and 0.001 for colon and rectal cancer, respectively). Theresult remained the same after adjustment of potentialconfounders (Fig 4).ConclusionsA sedentary lifestyle is associated with increased colonand rectal cancer risk in Hong Kong Chinese. Increases inphysical activity level resulted in progressive reduction inAll cases0%20%40%60%80%100%Colon cancers Rectal cancers Controls277286157166115117301300298104***114**221*Adjusted OR, 95% CI* 0.75, 0.58-0.97** 0.70, 0.51-0.95*** 0.78, 0.56-1.09<29.2 hours29.2-38.5 hours>38.5 hoursFig 1. Weekly duration of moderate to active physicalactivities in tertiles and colorectal cancer risk1st02nd 3rd0.20.40.60.81.01.21.41.6MET-hours in tertile (P for trend=0.005)Adjusted OR 1.020.63Colon cancers1st02nd 3rd0.20.40.60.81.01.2MET-hours in tertile (P for trend=0.023)Adjusted OR 0.760.68Rectal cancersFig 2. Weekly overall activity intensity with adjusted colon and rectal cancer riskHo et al10      Hong Kong Med J Vol 12 No 2 Supplement 1 April 2006All cases(P for trend0.002)0%20%40%60%80%100%Colon cancers(P for trend0.001)Rectal cancers ControlsAdjusted OR, 95% CI* 0.62, 0.41-0.95** 0.61, 0.39-0.95# 0.55, 0.34-0.90## 0.49, 0.29-0.83SedentaryLightMediumHeavy70201**42215108##2715587583642723742167877#157*Fig 3. Self-reported lifelong occupational activity level andcolorectal cancer risk00Number (P for trend 0.000)Adjusted OR0.20.40.60.81.01.21.41 2 3 4Colon cancers0.470.100.740.9100Number (P for trend 0.001)Adjusted OR0.20.40.60.81.01.21 2 3 4Rectal cancers0.520.00.550.70Fig 4. Adjusted colon and rectal cancer risk according to the number of target activity levels achievedboth colon and rectal cancer risk. These results remainedconsistent when different components, including overallactivity, occupation-related activity and leisure-timeexercise, were considered individually or in combination.Individuals who achieved two, three and four target activitylevels can reduce their colorectal cancer risk by 35%, 50%and >90%, respectively.AcknowledgementsThis study was funded by a grant from the Health ServicesResearch Fund (HSRF #721019). We would also like tothank Prof ED Janus for permitting the use of the question-naire and the data from the Hong Kong Cardiovascular RiskFactor Prevalence Study 1995-1996.1References1. Janus ED. Hong Kong Cardiovascular Risk Factor Prevalence Study,1995-1996. Hong Kong: Department of Clinical Biochemistry, TheUniversity of Hong Kong; 1997.2. Wong TK, Macfarlane DJ. Levels of habitual physical activityand exercise intensity during physical education class among 8-13-year-old Hong Kong primary school children. Res Q Exerc Sport(Suppl) 1997;68:A24.3. Hui WH. The health-promoting lifestyles of undergraduate nursesin Hong Kong. J Prof Nurs 2002;18:101-11.

A case-control study on environmental and familial risk factors for colorectal cancer in Hong Kong: physical activity reduces colorectal cancer risk

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A case-control study on environmental and familial risk factors for colorectal cancer in Hong Kong: physical activity reduces colorectal cancer risk

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