***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background : Existing data suggest that physical activity reduces colon cancer risk , but the association is not consistently observed in women . One potential explanation for this inconsistency is that hormone therapy , which is associated with lower colon cancer risk , acts as a modifier of the physical activity/colon cancer relationship . Methods : Participants in the California Teachers Study ( N = 120,147 ) , a prospect i ve cohort of female teachers and administrators residing in California , ages 22 to 84 years at baseline and with no prior history of colon cancer were eligible for study . Between 1996 and 2002 , 395 patients were diagnosed with invasive colon cancer . The relative risks ( RR ) associated with lifetime ( high school through age 54 years or current age ) and recent ( past 3 years ) strenuous and moderate recreational physical activity were estimated using Cox proportional hazards regression models . Results : Combined lifetime moderate and strenuous recreational physical activity was only modestly associated with colon cancer risk in the cohort [ ≥4 versus ≤0.5 h/wk/y : RR , 0.75 ; 95 % confidence interval , 0.57 - 1.00 ; Ptrend = 0.23 ] . Lifetime physical activity reduced colon cancer risk among postmenopausal women who had never taken hormone therapy ( ≥4 versus ≤0.5 h/wk/y : RR , 0.51 ; 95 % confidence interval , 0.31 - 0.85 ; Ptrend = 0.02 ) . Postmenopausal women with histories of hormone therapy use had lower colon cancer risk , but their risk was not associated with physical activity . The likelihood ratio test for interaction between hormone use and lifetime moderate plus strenuous physical activity was of borderline statistical significance ( P = 0.05 ) . We observed no effect modification by age , body mass index , smoking status , menopausal status , or folate intake . Conclusions : Lifetime recreational physical activity may protect against colon cancer among postmenopausal women who have never used hormone therapy . Among hormone therapy users , who have lower risk of colon cancer , recreational physical activity does not seem to provide any additional benefit . With declining rates of hormone therapy use , physical activity offers one possible means for reducing women 's colon cancer risk . ( Cancer Epidemiol Biomarkers Prev 2007;16(3):517–25 Physical activity may reduce colon cancer risk , but the underlying mechanisms remain unclear . Relating physical activity to cancer risk in anatomic segments of the colon may advance our underst and ing of possible mechanisms . We conducted a prospect i ve study of 59,369 Norwegian men and women who were followed up for cancer incidence and mortality . Cox proportional hazards models were used to estimate multivariably adjusted hazard ratios ( HR ) and 95 % confidence intervals ( 95 % CI ) . All statistical tests were two sided . During 17 years of follow-up , 736 colon cancers and 294 rectal cancers were diagnosed . Overall , we found an inverse association between  recreational physical activity  and colon cancer risk , but subsite analyses showed that the association was confined to cancer in the transverse and sigmoid colon . The adjusted HR , comparing people who reported high versus no physical activity , was 0.44 ( 95 % CI , 0.25 - 0.78 ) for cancer in the transverse colon and 0.48 ( 95 % CI , 0.31 - 0.75 ) for cancer in the sigmoid colon . The corresponding HR for cancer mortality was 0.33 ( 95 % CI , 0.14 - 0.76 ) for the transverse colon and 0.29 ( 95 % CI , 0.15 - 0.56 ) for the sigmoid colon . For rectal cancer , there was no association with physical activity in these data . In conclusion , the inverse association of recreational physical activity with cancer risk and mortality in the transverse and sigmoid segments of the colon may point at increased colon motility and reduced fecal transit time as possible underlying mechanisms . ( Cancer Epidemiol Biomarkers Prev 2008;17(1):183–8 Studies of colon cancer risk in males have reported strong positive associations with obesity , particularly with central adiposity . The association has been weaker and less consistent for women . In a prospect i ve cohort study of women , body measurements were taken directly ; fat mass and fat‐free mass being estimated by bioelectrical impedance analysis and central adiposity by waist circumference and waist‐to‐hip ratio ( WHR ) . Among 24,072 women followed on average for 10.4 years , 212 colon cancers were ascertained via the population cancer registry . We review ed medical records of all cases and classified them according to anatomic site and stage . The central adiposity measures of WHR ( hazard ratio per 0.1 unit increase = 1.31 , 95 % confidence interval ( CI ) 1.08–1.58 ) and waist circumference ( hazard ratio per 10 cm increase = 1.14 , 95 % CI 1.02–1.28 ) were positively associated with colon cancer risk . There was little or no association between other anthropometric measures and risk of colon cancer . There was some evidence that the associations were stronger for proximal tumors , but no evidence that risk differed by stage for any of the anthropometric measures . Central adiposity  appears to be associated with colon cancer risk in women . © 2005 Wiley‐Liss , Physical activity is protective against colon cancer , whereas colonic bile acid exposure is a suspected risk factor . Although likely related , the association between physical activity and bile acid levels has not been well-studied . Furthermore , the effect of triglycerides , which are known to modify bile acid levels , on this relationship has not been investigated . We conducted a cross-sectional analysis of baseline fecal bile acid levels  for 735 colorectal adenoma formers obtained from participants in a phase III ursodeoxycholic acid chemoprevention trial . Compared with the lowest quartile of recreational physical activity duration , the highest quartile was associated with a 17 % lower fecal bile acid concentration , adjusted for age , sex , dietary fiber intake , and body mass index ( P = 0.042 ) . Furthermore , consistent with a previously established relationship between serum triglyceride levels and bile acid metabolism , we stratified by triglyceride level and observed a 34 % lower fecal bile acid concentration ( highest versus lowest quartiles of physical activity ) in individuals with low triglycerides ( < 136 mg/dL ; P = 0.002 ) . In contrast , no association between physical activity and fecal bile acid concentration was observed for subjects with high triglycerides ( ≥136 mg/dL ) . Our results suggest that the biological mechanism responsible for the protective effect of physical activity  on the incidence of colon cancer may be partially mediated by decreasing colonic bile acid exposure . However , this effect may be limited to individuals with lower triglyceride levels . ( Cancer Epidemiol Biomarkers Prev 2009;18(5):1591–8 BACKGROUND Several studies of male colon cancer have found positive associations with body size and composition . It is uncertain whether this relationship is due to non-adipose mass , adipose mass , distribution of adipose mass such as central adiposity , or all three . METHODS In a prospect i ve cohort study of men aged 27 - 75 at recruitment in 1990 - 1994 , body measurements were taken by interviewers .  Fat mass and fat-free mass ( FFM ) were estimated from bioelectrical impedance analysis . Waist circumference and waist-to-hips ratio ( WHR ) estimated central adiposity . Incident colon cancers were ascertained via the population cancer registry . Altogether , 16,556 men contributed 145,433 person-years and 153 colon cancers . RESULTS Rate ratios ( RRs ) comparing men in the fourth quartile with those in the first quartile were as follows : FFM 2.3 [ 95 % confidence interval ( CI ) 1.4 - 3.7 ] ; height 1.9 ( 95 % CI 1.1 - 3.1 ) ; waist circumference 2.1 ( 95 % CI 1.3 - 3.5 ) ; WHR 2.1 ( 95 % CI 1.3 - 3.4 ) ; fat mass 1.8 ( 95 % CI 1.1 - 3.0 ) ; and body mass index 1.7 ( 95 % CI 1.1 - 2.8 ) . When continuous measures of FFM and WHR were modeled together , the RR for FFM per 10 kg was 1.37 ( 95 % CI 1.04 - 1.80 ) and the RR for WHR per 0.1 unit was 1.65 ( 95 % CI 1.28 - 2.13 ) . After adjustment for FFM and WHR , the RRs for fat mass and body mass index were no longer statistically significant . CONCLUSION Male colon cancer appears to be related to body size and composition by two different pathways , via central adiposity and via non-adipose mass Objective To prospect ively examine the association between physical activity and the risk of developing colorectal cancer in a large population -based cohort study of Japanese men and women , and to investigate whether the effects of physical activity on colorectal cancer risk differ by sex and subsite . Methods We analyzed data from a population -based cohort of 65,022 subjects . A total of 486 incident colorectal cancers ( 154 proximal colon , 166 distal colon and 149 rectal cancers ) was identified during 6 years of follow-up . Results We observed a significant inverse association between physical activity  and the risk of developing colorectal cancer , particularly colon cancer , among men . Relative to men in the lowest level of metabolic equivalent ( MET ) hours per day , those in the highest level had a RR of 0.69 ( 95 % CI = 0.49–0.97 ) . A significant decrease in risk of colorectal cancer was associated with increasing MET hours per day among men . This inverse association was essentially limited to colon cancer . A significant decrease in risk with increasing MET-hour score was observed predominantly for proximal colon cancer among men . In contrast , no significant decrease was seen among women . Conclusion These findings suggest that physical activity may prevent colon cancer among Japanese men Abstract Objective : Epidemiologic data relating obesity to risk  of colorectal cancer in women have been inconclusive . Two recent studies have suggested that the association may be modified by estrogen status ; BMI was positively associated with colorectal cancer risk among women with high estrogen exposures [ premenopausal women , and postmenopausal women who currently received postmenopausal hormone therapy ( PMH ) ]  . We prospect ively investigated the role of BMI in colorectal cancer risk along with the modifying effects of estrogen in a large cohort from the Women 's Health Study . Methods : Among 39,876 apparently healthy women aged ≥45 years at baseline ( 54 % of them were postmenopausal ) , 37,671 were eligible for the present study . During an average of 8.7 years of follow-up , 202 women had a confirmed diagnosis of colorectal cancer . Baseline BMI was calculated by dividing self-reported weight in kilograms by height in meters squared . Results : The multivariate relative risks ( RRs ) and 95 % confidence interval ( CI ) of colorectal cancer were 1.72 ( 1.12–2.66 ) for 27–29.9 kg/m2 , and 1.67 ( 1.08–2.59 ) for ≥30 kg/m2 , as compared with BMI < 23 kg/m2(p for trend = 0.02 ) . This positive association was seen primarily in the proximal colon ( p for trend = 0.004 ) . When the association was further examined according to PMH use among postmenopausal women , we found that both current and never users with higher BMI were at a greater risk of colorectal cancer ( p for interaction between BMI and PMH use = 0.33 ) . As compared with BMI < 23 kg/m2 , the multivariate RRs and 95 % CI for 27–29.9 and ≥30 kg/m2 were 1.98 ( 0.98–3.99 ) and 1.41 ( 0.65–3.06 ) among current users , and 1.05 ( 0.42–2.65 ) and 2.91 ( 1.40–6.06 ) among never users . Conclusions : These data suggest that higher BMI was associated with an elevated risk of colorectal cancer , and the positive relationship was not altered by estrogen exposure among postmenopausal women Anthropometric factors have been associated with colorectal cancer and adenomas but with conflicting results in women or regarding adenoma characteristics . The authors aim ed to explore associations between anthropometric factors ( height , weight , body mass index , waist and hip circumferences , and weight changes ) and adenoma risk . They analyzed the 17,391 women of the French Etude épidémiologique des femmes de la Mutuelle Générale de l'Education Nationale (E3N)-European Prospect i ve Investigation into Cancer and Nutrition ( EPIC ) cohort who underwent a colonoscopy during follow-up ( 1993 - 2002 ) , including 1,408 who developed a first colorectal adenoma . In Cox multivariate proportional hazard regression models , obesity was associated with an increased colorectal adenoma risk ( hazard ratio = 1.53 , 95 % confidence interval : 1.21 , 1.94 ) . This association was restricted to left colon adenomas ( P( 
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In conclusion , the results suggest minor differences in the associations of BMI and the risk of cancer between the colorectal subsites .
For physical activity , the association does not seem to differ between the colonic subsites , but a difference was observed between the colon and the rectum , perhaps indicating that different mechanisms are operating in the development of colon and rectal cancer