Physical activity and occupational risk of colon cancer in Shanghai, China

Prospective Analyses of Sedentary Behavior in Relation to Risk of Ovarian Cancer

We examined the association of sedentary behavior with risk of ovarian cancer overall, by tumor subtype, and by participant characteristics in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II). A total of 69,558 NHS participants (1992-2016) and 104,130 NHS II participants (1991-2015) who reported on time spent sitting at home, at work, and while watching television were included in the analysis, which included 884 histologically confirmed ovarian cancer cases. Multivariable-adjusted Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for ovarian cancer by sitting time (no mutual adjustment for individual sitting types in primary analyses). We examined potential heterogeneity by tumor histological type (type I or II), body mass index (weight (kg)/height (m)2; < 25 or ≥25), and total physical activity (<15 or ≥15 metabolic equivalent of task-hours/week). We observed an increased risk of ovarian cancer for women who sat at work for 10-19 hours/week (HR = 1.25, 95% CI: 1.04, 1.51) and ≥20 hours/week (HR = 1.40, 95% CI: 1.14, 1.71) versus <5 hours/week. This association did not vary by body mass index, physical activity, or histotype (P for heterogeneity ≥ 0.43). No associations were observed for overall sitting, sitting while watching television, or other sitting at home. Longer sitting time at work was associated with elevated risk of ovarian cancer. Further investigations are required to confirm these findings and elucidate underlying mechanisms.

Occupational sitting time and subsequent risk of cancer: The Japan Public Health Center-based Prospective Study

Although occupational sitting time has been associated with adverse health outcomes and mortality, the association with cancer incidence remains unknown. This study investigated the association between occupational sitting time and risk of total and site‐specific cancer in a Japanese population. We evaluated 33 307 participants aged 50‐79 years who responded to a questionnaire in 2000‐2003 in the Japan Public Health Center‐based Prospective Study and were followed until 2013. Participants were grouped by sitting time at work. Hazard ratio (HR) and 95% confidence interval (CI) of cancer incidence were calculated with adjustment for potential confounders including moderate‐to‐vigorous physical activity. During 10.2 years of follow‐up, 3807 newly diagnosed cases of cancer were identified. Occupational sitting time was marginally associated with total cancer, with multivariable HRs for the ≥7 h/d vs 1 to <3 h/d category of 1.12 (95% CI, 0.99‐1.26; P for trend = .071) in men, but not women. Among findings for cancers at specific sites, long occupational sitting time was associated with increased risk of pancreas cancer, with multivariable HRs for the ≥7 h/d vs 1 to <3 h/d category of 2.25 (95% CI, 1.17‐4.34; P for trend = .021) in men, and lung cancer, with multivariable HRs for the ≥7 h/d vs 1 to <3 h/d category of 2.80 (95% CI, 1.33‐5.90; P for trend = .013) in women. Extended sitting time at work was associated with an increased risk of pancreas cancer in men and lung cancer in women.

Prevalence of pre-cancerous colon lesions in referred patients under patronage of a local relief foundation in Guilan province

Colon cancer is the most commonly diagnosed gastrointestinal cancers in developed countries with varied incidence and the onset age of disease worldwide. Overall, 161 participants who were under patronage of a local relief foundation and referred to the endoscopy ward of Razi Hospital affiliated to the Guilan University of Medical Sciences. These patients have been aged more than 50 or more than 40 years with history of colorectal cancer in their first-degree family were enrolled from March 2016–March 2017. Demographic information were collected. Colonoscopy was performed and histopathological evaluation of observed lesions and polyps was done. Most of participants were female (113 individuals, 70.2%) and aged 50–60 years (83 individuals, 51.6%). Seventy-four (46%) had certain lesions. Most of colonoscopy findings were observed in the ascending colon in which depressed polyps and diverticulum were most frequent. However, rectum showed the most histological findings. All polyps of descending and ascending colons were neoplastic, while most of rectal polyps were non-neoplastic. Male patients, who were aged more than 60 years and smokers had significant higher percentage of both lesions and polyps in their colon (p<0.05). Moreover, significant positive association was detected between exposure to harmful industries and having polyps (p=0.01). We found male gender, higher age, smoking, and exposure to harmful industries as important risk factors for having colorectal lesions, which must be confirmed in further studies.

Domain-specific physical activity and sedentary behaviour in relation to colon and rectal cancer risk: a systematic review and meta-analysis

Background

Physical activity is associated with reduced risk of colorectal cancer, but most epidemiological studies have focused on occupational and recreational physical activity. The evidence for other domains of activity, and for sedentary behaviour, is limited.

Methods

Medline, Embase and Web of Science were searched from inception to December 2015 for studies examining domain-specific physical activity or sedentary behaviour and the risk of colon and/or rectal cancer. We extracted maximally adjusted relative risks (RRs) except when RRs not adjusted for body mass index, were also presented. We used random-effects meta-analysis to compute pooled RRs comparing the highest versus the lowest level of exposure. We used meta-regression to assess sources of heterogeneity in estimates.

Results

We identified 17 cohort and 21 case-control studies, of which 17 had occupational data, 23 had recreational data, three each had data on transport and household physical activity domains, and 6 studies had data on occupational sedentary behaviour. The pooled relative risks (RRs) for colon cancer were 0.74 (95% confidence interval (CI): 0.67, 0.82) for occupational activity, 0.80 (95% CI: 0.71, 0.89) for recreational activity, 0.66 (95% CI: 0.45, 0.98) for transport-related physical activity, 0.85 (95% CI: 0.71, 1.02) for household physical activity, and 1.44 (95% CI: 1.28, 1.62) for occupational sedentary behaviour. For rectal cancer, the pooled RRs were 0.88 (95% CI: 0.79, 0.98) for occupational activity, 0.87 (95% CI: 0.75, 1.01) for recreational activity, 0.88 (95% CI: 0.70, 1.12) for transport-related physical activity, 1.01 (95% CI: 0.80, 1.27) for household physical activity, and 1.02 (95% CI: 0.82, 1.28) for occupational sedentary behaviour.

Conclusions

In addition to increasing occupational and recreational physical activity, promoting physical activity during transport and reducing sedentary behaviour in the workplace may also be useful colorectal cancer prevention strategies.

Physical activity, sedentary time, and risk of colorectal cancer: the Singapore Chinese Health Study

Singapore has experienced a marked increase in colorectal cancer incidence over the past 40 years. Evidence from prospective studies in Western Europe and the USA suggests that low physical activity and high amounts of sedentary time are associated with increased colorectal cancer risk. The aim of this study is to evaluate these relationships in an Asian population. The Singapore Chinese Health Study enrolled 63 257 adults between 1993 and 1998. At enrollment, participants reported past year physical activity and time spent sitting. Incident colorectal cancers (n=1994) were identified through 31 December 2014. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) adjusted for potential confounders. Any strenuous-vigorous or moderate physical activity was reported by 13.7 and 22.1% of the cohort, respectively. Strenuous-vigorous physical activity was associated with statistically significant reduced colorectal cancer risk (HR=0.85; 95% CI: 0.74-0.99 for ≥0.5 h/week vs. none), but moderate was not. In analysis stratified by time spent watching television, an inverse relationship between moderate physical activity and colorectal cancer risk (HR=0.86; 95% CI: 0.72-1.01 for ≥0.5 h/week vs. none) was observed for those who reported at least 3 h/day sitting watching television (Pinteraction=0.042). Participation in strenuous-vigorous physical activity, such as jogging, swimming, or heavy manual labor, was associated with reduced colorectal cancer risk among Singapore Chinese. Further research on physical activity and sedentary behaviors, independently and in combination, and colorectal cancer risk in Asian populations is needed.

Physical activity, sedentary time, and risk of colorectal cancer: the Singapore Chinese Health Study

Singapore has experienced a marked increase in colorectal cancer incidence over the past 40 years. Evidence from prospective studies in Western Europe and the USA suggests that low physical activity and high amounts of sedentary time are associated with increased colorectal cancer risk. The aim of this study is to evaluate these relationships in an Asian population. The Singapore Chinese Health Study enrolled 63 257 adults between 1993 and 1998. At enrollment, participants reported past year physical activity and time spent sitting. Incident colorectal cancers (n=1994) were identified through 31 December 2014. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) adjusted for potential confounders. Any strenuous-vigorous or moderate physical activity was reported by 13.7 and 22.1% of the cohort, respectively. Strenuous-vigorous physical activity was associated with statistically significant reduced colorectal cancer risk (HR=0.85; 95% CI: 0.74-0.99 for ≥0.5 h/week vs. none), but moderate was not. In analysis stratified by time spent watching television, an inverse relationship between moderate physical activity and colorectal cancer risk (HR=0.86; 95% CI: 0.72-1.01 for ≥0.5 h/week vs. none) was observed for those who reported at least 3 h/day sitting watching television (Pinteraction=0.042). Participation in strenuous-vigorous physical activity, such as jogging, swimming, or heavy manual labor, was associated with reduced colorectal cancer risk among Singapore Chinese. Further research on physical activity and sedentary behaviors, independently and in combination, and colorectal cancer risk in Asian populations is needed.

Increasing Nonsedentary Behaviors in University Students Using Text Messages: Randomized Controlled Trial

BACKGROUND

Sedentary behavior (SB) has been linked to many health problems such as type 2 diabetes and heart disease. Increasing the length and frequency of breaks from sitting and increasing the time spent standing and engaged in light and moderate physical activity are ways to decrease SB. Text message-based interventions have succeeded in aiding smoking cessation and increase both physical activity and healthy eating, but they have not been shown to reduce SB.

OBJECTIVE

The primary purpose of this pilot study was to determine the effectiveness of a text message-based intervention in increasing nonsedentary behaviors in university students. A secondary purpose was to (1) determine whether the intervention could enhance self-efficacy beliefs for decreasing SB and (2) whether these efficacious beliefs could predict actual SB.

METHODS

Eighty-two university students were recruited via mass emails and randomized into intervention (SB-related text messages) or control (text messages unrelated to SB) groups. Participants received daily text messages scheduled by the researcher encouraging breaks from sitting, standing, light- and moderate-intensity physical activity (PA). They then reported various SBs via Web-based questionnaires at four time points (baseline, 2, 4, and 6 weeks). Self-efficacious beliefs toward taking breaks from sitting and decreasing the amount of time spent sitting were assessed at the same time points.

RESULTS

Last observation carried forward (LOCF) method was used for incomplete data as an intent-to-treat (ITT) analysis (intervention group n=15, control group n=11). Small-to-moderate effects favoring the text intervention group were found at 6 weeks for break frequency -14.64 minutes, break length +.59 minutes, standing +24.30 min/day, light-intensity +74.34 min/day, and moderate-intensity + 9.97 min/day PA. Only light-intensity PA approached significance (P=.07). Self-efficacy beliefs also favored the text intervention group and reached significance (P=.032) for sitting less. Significant (P<.05) relations were found between the self-efficacy constructs and breaks, standing, and light or moderate PA.

CONCLUSIONS

Text messages have the potential to increase nonsedentary behaviors in university students. These messages can increase self-efficacy beliefs to take more breaks and reduce sitting time. Efficacious beliefs can predict actual SB and to a lesser extent light- and moderate-intensity PA.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02562937; https://clinicaltrials.gov/ct2/show/NCT02562937 (Archived by WebCite at http://www.webcitation.org/6jVLwXE5M).

Television watching and risk of colorectal adenoma

Background:

Prolonged TV watching, a major sedentary behaviour, is associated with increased risk of obesity and diabetes and may involve in colorectal carcinogenesis.

Methods:

We conducted a cross-sectional analysis among 31 065 men with ⩾1 endoscopy in the Health Professionals Follow-up Study (1988–2008) to evaluate sitting while watching TV and its joint influence with leisure-time physical activity on risk of colorectal adenoma. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

Results:

Prolonged sitting while watching TV was significantly associated with increased risk of colorectal adenoma (n=4280), and adjusting for physical activity or a potential mediator body mass index did not change the estimates. The ORs (95% CIs) across categories of TV watching (0–6, 7–13, 14–20, and 21+ h per week) were 1.00 (referent), 1.09 (1.01–1.17), 1.16 (1.06–1.27), and 1.10 (0.97–1.25) (OR per 14-h per week increment=1.11; 95% CI: 1.04–1.18; P_trend=0.001). Compared with the least sedentary (0–6 h per week of TV) and most physically active (highest quintile) men, the most sedentary (14+ h per week) and least active (lowest quintile) men had a significant increased risk of adenoma (OR=1.25; 95% CI: 1.05–1.49), particularly for high-risk adenoma.

Conclusions:

Prolonged TV viewing is associated with modest increased risk of colorectal adenoma independent of leisure-time physical activity and minimally mediated by obesity.

Television viewing and time spent sedentary in relation to cancer risk: a meta-analysis

BACKGROUND

Sedentary behavior is emerging as an independent risk factor for chronic disease and mortality. However, the evidence relating television (TV) viewing and other sedentary behaviors to cancer risk has not been quantitatively summarized.

METHODS

We performed a comprehensive electronic literature search in Cochrane, EMBASE, Medline, and SciSearch databases through February 2014 for published articles investigating sedentary behavior in relation to cancer incidence. Because randomized controlled trials are difficult to perform on this topic, we focused on observational studies that met uniform inclusion criteria. Data were extracted independently by both authors and summarized using random-effects meta-analysis and meta-regression. All statistical tests were two-sided.

RESULTS

Data from 43 observational studies including a total of 68936 cancer cases were analyzed. Comparing the highest vs lowest levels of sedentary time, the relative risks (RRs) for colon cancer were 1.54 (95% confidence interval [CI] = 1.19 to 1.98) for TV viewing time, 1.24 (95% CI = 1.09 to 1.41) for occupational sitting time, and 1.24 (95% CI = 1.03 to 1.50) for total sitting time. For endometrial cancer, the relative risks were 1.66 (95% CI = 1.21 to 2.28) for TV viewing time and 1.32 (95% CI = 1.08 to 1.61) for total sitting time. A positive association with overall sedentary behavior was also noted for lung cancer (RR = 1.21; 95% CI = 1.03 to 1.43). Sedentary behavior was unrelated to cancers of the breast, rectum, ovaries, prostate, stomach, esophagus, testes, renal cell, and non-Hodgkin lymphoma.

CONCLUSIONS

Prolonged TV viewing and time spent in other sedentary pursuits is associated with increased risks of certain types of cancer.

Colon transit time according to physical activity level in adults

BACKGROUND/AIMS

Physical activity (PA) is associated with a reduced risk of colorectal cancer. Thus, we examined the colon transit time (CTT) according to the physical activity level (PAL) in Korean adults.

METHODS

The study subjects were 49 adults: 24 males and 25 females. The subjects used an accelerometer for 7 consecutive days to measure the 1-week PAL. The subjects took a capsule containing 20 radio-opaque markers for 3 days. On the fourth day, a supine abdominal radiography was performed. According to the total activity count of all study subjects, the upper 25%, middle 50% and lower 25% were classified into the high (H), moderate (M) and low (L) physical activity (PA) groups, respectively.

RESULTS

The total CTT was significantly longer in the female (25.8 hours) than in the male subjects (7.4 hours) (P = 0.002). In regard to difference on PAL, although there was no significant difference among the male subjects, the right CTT in the female subjects was significantly shorter in H group than in M group (P = 0.048), and the recto-sigmoid CTT was significantly shorter in H group than in L group (P = 0.023). Furthermore, there were significant differences in total CTT between L and M groups (P = 0.022), M and H groups (P = 0.026) and between L and H groups (P = 0.002).

CONCLUSIONS

The female, but not male, subjects showed that moderate and high PAL assisted colon transit.

Identification of occupational cancer risks in British Columbia, Canada: a population-based case-control study of 1,155 cases of colon cancer

Objective

Cancer has been recognized to have environmental origin, but occupational cancer risk studies have not been fully documented. The objective of this paper was to identify occupations and industries with elevated colon cancer risk based on lifetime occupational histories collected from 15,463 incident cancer cases.

Method

A group matched case-control design was used. All cases were diagnosed with histologically proven colon cancers, with cancer controls being all other cancer sites, excluding rectum, lung and unknown primary, diagnosed at the same period of time from the British Columbia Cancer Registry. Data analyses were done on all 597 Canadian standard occupation titles and 1,104 standard industry titles using conditional logistic regression for matched data sets and the likelihood ratio test.

Results

Excess colon cancer risks was observed in a number of occupations and industries, particularly those with low physical activity and those involving exposure to asbestos, wood dusts, engine exhaust and diesel engine emissions, and ammonia.

Discussion

The results of our study are in line with those from the literature and further suggest that exposure to wood dusts and to ammonia may carry an increased occupational risk of colon cancer.

Physical activity and breast cancer risk in Chinese women

Background:

The influence of different types and intensities of physical activity on risk for breast cancer is unclear.

Methods:

In a prospective cohort of 73 049 Chinese women (40–70 years), who had worked outside the home, we studied breast cancer risk in relation to specific types of self-reported and work history-related physical activity, including adolescent and adult exercise and household activity and walking and cycling for transportation. Occupational sitting time and physical activity energy expenditure were assigned based on lifetime occupational histories.

Results:

In all, 717 incident breast cancer cases were diagnosed. Breast cancer risk was lower for women in the lowest quartile of average occupational sitting time and in the highest quartile of average occupational energy expenditure (adjusted hazard ratio (HR): 0.81 and 0.73, respectively, P⩽0.05). Adult exercise at or above the recommended level (8 metabolic equivalent (MET) h per week per year) was associated with lower risk (adjusted HR: 0.73, P<0.05) in post-menopausal women. Analysis of joint effects showed that having both an active job and exercise participation did not confer an additional benefit. Other common daily activities were not associated with lower risk.

Interpretation:

These findings suggest that both exercise and occupational activity are associated with lower breast cancer risk, which supports current health promotion campaigns promoting exercise.

Lifestyle factors and colorectal cancer risk (2): a systematic review and meta-analysis of associations with leisure-time physical activity

OBJECTIVE

Increased physical activity may decrease the risk of colorectal cancer. As a prerequisite to the determination of lifestyle attributable risks, we performed a systematic review and meta-analysis of prospective observational studies to quantify gender-specific risk associated with increased leisure-time physical activity (LT-PA).

METHOD

We searched MEDLINE and EMBASE (to December 2007), and other sources, selecting reports based on strict inclusion criteria. We used random-effects meta-analyses to estimate summary risk ratios (RR) and 95% confidence intervals (95% CI) for uppermost vs lowermost categories of physical activity. To investigate dose-response, we explored risks ratios as a function of cumulative percentiles of physical activity distribution.

RESULTS

Fifteen datasets from 14 articles, including 7873 incident cases, were identified. For colon cancer, there were inverse associations with LT-PA for men (RR: 0.80; 95% CI: 0.67-0.96) and women (0.86; 0.76-0.98). LT-PA did not influence risk of rectal cancer. The dose-response analysis was consistent with linear pattern reductions in risk of colon cancer in both genders. There was evidence of moderate between-study heterogeneity but summary estimates were broadly consistent across potential confounding factors.

CONCLUSION

Increased LT-PA is associated with a modest reduction in colon but not rectal cancer risk; a risk reduction, which previously may have been overstated. LT-PA only interventions in public health cancer prevention strategies are unlikely to impact substantially on colorectal cancer incidences.

Anthropometric measurements, physical activity, and the risk of symptomatic gallstone disease in Chinese women

PURPOSE

Gallstone disease is more common among overweight individuals, particularly in women. We conducted a cross-sectional case-control study of Chinese women nested in the Shanghai Women's Health Study (SWHS) to evaluate the association of gallstone disease with body mass index (BMI), waist to hip ratio (WHR), and physical activity (PA).

METHODS

The study included 8,485 women with self-reported, physician-diagnosed, prevalent gallstone disease and 16,970 frequency-matched controls by birth year and age at gallstone diagnosis (4-year intervals). Information on height, weight history, waist and hip circumferences, physical activities, and other exposures was obtained by in-person interview.

RESULTS

: Usual BMI (p trend < 0.001) and WHR (p trend < 0.001) were both related to a high prevalence of gallstone disease, and a significant interaction between BMI and WHR on gallstone risk was found (odds ratio [OR] = 3.82, 95%CI [95% confidence interval] 2.47-5.23 for those with both highest BMI and WHR relative to those with lowest BMI and WHR, p interaction = 0.03). Gallstone risk was positively associated with cumulative occupational sitting time (p trend = 0.01) and inversely associated with occupational cumulative energy expenditure (p trend = 0.03) as well as with household PA (p trend = 0.02).

CONCLUSIONS

Our findings further support that overall and central excessive adiposity is an independent risk factor for gallstones in women. In addition, regardless of adiposity level, being physically active may ameliorate the risk of this disease.

Physical activity and risk of colon and rectal cancers: the European prospective investigation into cancer and nutrition

We investigated several aspects of the role of physical activity in colon and rectal cancer etiology that remain unclear in the European Prospective Investigation into Nutrition and Cancer. This cohort of 413,044 men and women had 1,094 cases of colon and 599 cases of rectal cancer diagnosed during an average of 6.4 years of follow-up. We analyzed baseline data on occupational, household, and recreational activity to examine associations by type of activity, tumor subsite, body mass index (BMI), and energy intake. The multivariate hazard ratio for colon cancer was 0.78 [95% confidence interval (95% CI), 0.59-1.03] among the most active participants when compared with the inactive, with evidence of a dose-response effect (P(trend) = 0.04). For right-sided colon tumors, the risk was 0.65 (95% CI, 0.43-1.00) in the highest quartile of activity with evidence of a linear trend (P(trend) = 0.004). Active participants with a BMI under 25 had a risk of 0.63 (95% CI, 0.39-1.01) for colon cancer compared with the inactive. Finally, an interaction between BMI and activity (P(interaction) = 0.03) was observed for right-sided colon cancers; among moderately active and active participants with a BMI under 25, a risk of 0.38 (95% CI, 0.21-0.68) was found as compared with inactive participants with BMI >30. No comparable decreased risks were observed for rectal cancer for any type of physical activity for any subgroup analyses or interactions considered. We found that physical activity reduced colon cancer risk, specifically for right-sided tumors and for lean participants, but not rectal cancer.

Physical activity and risk of colon cancer in a cohort of Danish middle-aged men and women

OBJECTIVE

To investigate the effects of occupational activity and leisure time activity on incident colon cancer risk in a Danish middle-aged population.

METHODS

In the cohort, Diet, Cancer and Health, which included 28,356 women and 26,122 men aged 50-64 years at baseline, 140 women and 157 men were diagnosed with colon cancer from 1993 to 2003. The associations between occupational and leisure time activity in terms of a MET-score and the single activities, sports, cycling, walking, gardening, housework and do-it-yourself work, and incident colon cancer were investigated. Leisure time activity was investigated in two ways using the Cox proportional hazards model: by comparison of active versus non-active and by investigating a possible dose-response relationship while allowing a separate association for non-active individuals.

RESULTS

No associations were found between risk of colon cancer and occupational activity, MET-hours per week of total leisure time activity, residuals from a regression of each activity on the total MET-hours or the time spent on any of the six types of leisure time activities. However, a borderline significant association was found with the number of activities in which the participants were active. For each additional activity IRR = 0.87 (0.76-1.00) for women and IRR = 0.88 (0.78-1.00) for men.

CONCLUSION

Our data do not support the evidence of an inverse association between colon cancer risk and occupational activity or leisure time activity, but avoiding a sedentary lifestyle by participating in different activities may reduce colon cancer risk.

Physical activity and the risk of colon cancer among women: a prospective cohort study (United States)

Physical activity has frequently been reported to decrease the risk of colon cancer in men, but data on the relation of physical activity to colon cancer risk in women have generally been less consistent. To further investigate the relationship of physical activity with colon cancer risk in women, we studied a cohort of 31,783 US women participating in the Breast Cancer Detection Demonstration Project Follow-up Study. Information on daily physical activity over the past year was ascertained using a self-administered questionnaire at study baseline. The Cox proportional hazards model was used to estimate relative risks (RRs) relating physical activity to the risk of incident colon cancer. During 270,325 person-years of follow-up, 243 colon cancer cases were identified. No association was observed between physical activity and the subsequent risk of colon cancer. The multivariable RRs of colon cancer across increasing quintiles of total physical activity were 1.0, 1.45, 1.16, 1.27 and 1.15 (95% CI: 0.76, 1.75; p(trend) = 0.77). The multivariable RRs comparing women at the extremes of moderate and vigorous physical activity, respectively, were 1.07 (95% CI: 0.70, 1.62) and 1.10 (95% CI: 0.78, 1.55). The relationship between physical activity and colon cancer risk did not vary by anatomic subsite or across subgroups defined by age, body mass, dietary fiber intake, menopausal status, menopausal hormone use or aspirin use. The results of this large prospective cohort study among women do not support the hypothesis that physical activity is related to a lower incidence of colon cancer.

A meta-analysis of the association of physical activity with reduced risk of colorectal cancer

BACKGROUND

Physical activity may be associated with reduced risk of colorectal cancer. The main aim of this paper is to review the available evidence for a link between exercise and large bowel cancer.

METHODS

A Cochrane-type methodology was performed. Data extracted included, type of study, type of physical activity measured and the numerical results. The risk ratios (RR) of the studies have been pooled according to the type of study, type of exercise, type of cancer and sex. Pooling was undertaken using fixed effect meta-analysis. A random effect meta-analysis was used where substantial heterogeneity existed.

RESULT

Data from 19 cohort studies showed a statistically significant reduction in the risk of colon cancer in physically active males, RR being 0.79 (95% CI 0.72-0.87) and 0.78 (95% CI 0.68-0.91) for occupational and recreational activities, respectively. In women only recreational activities are protective against colon cancer (RR = 0.71, 95%CI 0.57-0.88). Case-control studies showed significantly reduced risks of colon cancer in both sexes irrespective of the type of activity. No protection against rectal cancer is seen in either sex.

CONCLUSION

There is considerable evidence that physical activity is associated with reduced risk of colon cancer in both males and females.

Primary prevention of colorectal cancer: lifestyle, nutrition, exercise

The past two decades have provided a vast amount of literature related to the primary prevention of colorectal cancer. Large international variation in colorectal cancer incidence and mortality rates and the prominent increases in the incidence of colorectal cancer in groups that migrated from low- to high-incidence areas provided important evidence that lifestyle factors influence the development of this malignancy. Moreover, there is convincing evidence from epidemiological and experimental studies that dietary intake is an important etiological factor in colorectal neoplasia. Although the precise mechanisms have not been clarified, several lifestyle factors are likely to have a major impact on colorectal cancer development. Physical inactivity and to a lesser extent, excess body weight, are consistent risk factors for colon cancer. Exposure to tobacco products early in life is associated with a higher risk of developing colorectal neoplasia. Diet and nutritional factors are also clearly important. Diets high in red and processed meat increase risk. Excess alcohol consumption, probably in combination with a diet low in some micronutrients such as folate and methionine, appear to increase risk. There is also recent evidence supporting a protective effect of calcium and vitamin D in the etiology of colorectal neoplasia. The relationship between intake of dietary fiber and risk of colon cancer has been studied for three decades but the results are still inconclusive. However, some micronutrients or phytochemicals in fiber-rich foods may be important; folic acid is one such micronutrient that has been shown to protect against the development of colorectal neoplasia and is currently being studied in intervention trials of adenoma recurrence. The overwhelming evidence indicates that primary prevention of colon cancer is feasible. Continued focus on primary prevention of colorectal cancer, in combination with efforts aimed at screening and surveillance, will be vital in attaining the greatest possible progress against this complex, yet highly preventable disease.

Contraceptive methods and induced abortions and their association with the risk of colon cancer in Shanghai, China

267400 female textile workers in Shanghai, who were administered a questionnaire at enrollment into a randomised trial of breast self-examination between October 1989 and October 1991, were followed up until the middle of 2000. Based on the 655 women who developed colon cancer, rate ratios (RRs) were estimated and trends in risk assessed using Cox Proportional Hazards Models. Risk was increased in women who used oral contraceptives for over 3 years (RR=1.56, 95% Confidence Interval (CI) 1.01-2.40). A possible increase in risk was also observed in women who received progestational injections during pregnancy (RR=1.24, 95% CI 0.95-1.62), but not in relation to the use of injectable contraceptives. A possible reduction in risk was associated with tubal ligation (RR=0.86, 95% CI 0.71-1.03) and ever having had an induced abortion (RR=0.84, 95% CI 0.71-1.00). No trends in risk were observed in relation to the duration of hormonal contraceptive use or the number of induced abortions. Additional studies of the possible roles contraceptives may play in the aetiology of colon cancer in women at low risk of this disease are warranted.

Occupational physical activity across occupational categories

This study investigated the amount of physical activity that occurs during normal working hours, highlighting the occupational differences in physical activity by occupational category. Data were collected by means of a self-administered questionnaire (Tecumseh Occupational Physical Activity Questionnaire [TOQ]), which measures past year Occupational Physical Activity (OPA) and by a motion-sensing device (Yamax DigiWalker Pedometer SW - 700). Ninety male and female participants aged 18-62 years participated in the study. Participants were stratified by occupational category according to the Australian Standard Classification of Occupations (ASCO), which was then condensed into professional, white-collar and blue-collar workers. The results showed significant (p < .05) increases in OPA from the professional category (least active) through to the blue-collar workers (most active) in terms of walking activity. Mean daily step counts were 2,835, 3,616 and 8,757 for professional, white-collar and blue-collar respectively. Occupational Physical Activity Scores and Work Activity Units (WAU) in MET - min x wk(-1) from the TOQ showed similar patterns, with blue collar reporting significantly (p < .05) more past year OPA than their white-collar and professional workers. Significant correlations were also shown between the pedometer (step-count data) and the TOQ (r = .38 - .74, p < .01).

Time trends in cancer mortality in China: 1987-1999

A first analysis of time trends in cancer mortality in China at the national level is presented. Using a joinpoint regression model, based on data from a national mortality routine reporting system in China (CHIS), time trends in mortality for 9 major cancers are analyzed. Between 1987 and 1999, the age-standardized mortality rates for all cancers combined declined slightly in rural areas but have increased since 1996 in urban areas. The mortality rates for cancers in oesophagus, stomach, cervix uteri, leukaemia (except for urban males after 1996) and nasopharynx declined, while lung cancer and female breast cancer showed significant increasing trends in both urban and rural areas and for both sexes. Cancers of the colon-rectum and liver had different trends in mortality in urban and rural populations. The trends in age-specific mortality rates suggest some different trends in the younger population, which may presage future overall trends, for example, increasing mortality from cancer of the cervix. The observed trends primarily reflect the dramatic changes in socioeconomic circumstances and lifestyles in China in the last 2 decades. Tobacco smoking remains a major problem, with increases in mortality from lung cancer. The improvements in socioeconomic status, diet and nutrition may be responsible for the declining risk of some cancers (oesophagus, stomach and nasopharynx), while increasing the risk for others (breast and colon-rectum). Screening programs (especially for cervix cancer), and more available and better facilities for cancer therapy, may have helped to reduce mortality for several cancers. The large increases in the absolute number of deaths that resulted from the increasing and aging population are much more important in determining the future cancer burden than any changes due to change in risk, emphasizing the increasing importance of cancer as a health problem in the 21st century in China.

Physical activity and cancer prevention: etiologic evidence and biological mechanisms

Scientific evidence is accumulating on physical activity as a means for the primary prevention of cancer. Nearly 170 observational epidemiologic studies of physical activity and cancer risk at a number of specific cancer sites have been conducted. The evidence for decreased risk with increased physical activity is classified as convincing for breast and colon cancers, probable for prostate cancer, possible for lung and endometrial cancers and insufficient for cancers at all other sites. Despite the large number of studies conducted on physical activity and cancer, most have been hampered by incomplete assessment of physical activity and a lack of full examination of effect modification and confounding. Several plausible hypothesized biological mechanisms exist for the association between physical activity and cancer, including changes in endogenous sexual and metabolic hormone levels and growth factors, decreased obesity and central adiposity and possibly changes in immune function. Weight control may play a particularly important role because links between excess weight and increased cancer risk have been established for several sites, and central adiposity has been particularly implicated in promoting metabolic conditions amenable to carcinogenesis. Based on existing evidence, some public health organizations have issued physical activity guidelines for cancer prevention, generally recommending at least 30 min of moderate-to-vigorous intensity physical activity on > or =5 d/wk. Although most research has focused on the efficacy of physical activity in cancer prevention, evidence is increasing that exercise also influences other aspects of the cancer experience, including cancer detection, coping, rehabilitation and survival after diagnosis.

Physical activity and cancer risk: dose-response and cancer, all sites and site-specific

PURPOSE

The association between physical activity and overall and site-specific cancer risk is elaborated in relation to whether any observed dose-response association between physical activity and cancer can be interpreted in terms of how much physical activity (type, intensity, duration, frequency) is needed to influence site- and gender-specific cancer risk.

METHODS

Observational studies were reviewed that have examined the independent effect of the volume of occupational physical activity (OPA) and/or leisure time physical activity (LPA) on overall and site-specific cancer risk.

RESULTS

The evidence of cohort and case-control studies suggests that both leisure time and occupational physical activity protect against overall cancer risk, with a graded dose-response association suggested in both sexes. Confounding effects such as diet, body weight, and parity are often included as a covariate in the analyses, with little influence on the observed associations. A crude graded inverse dose-response association was observed between physical activity and colon cancer in 48 studies including 40,674 colon/colorectal cancer cases for both sexes. A dose-response effect of physical activity on colon cancer risk was especially observed, when participation in activities of at least moderate activity (>4.5 MET) and demonstrated by activities expressed as MET-hours per week. An observed inverse association with a dose-response relationship between physical activity and breast cancer was also identified in the majority of the 41 studies including 108,031 breast cancer cases. The dose-response relationship was in particular observed in case-control studies and supported by observations in cohort studies when participation in activities of at least moderate activity (>4.5 MET) and demonstrated by activities expressed by MET-hours per week. This association between physical activity and breast cancer risk is possibly dependent on age at exposure, age at diagnosis, menopausal status and other effect modifiers, e.g., body mass index. Furthermore, data concerning carcinoma of other cancers (prostate, lung, endometrium, ovary, and testicular cancers) are required.

CONCLUSION

A protective effect of physical activity on site-specific cancer risk with a dose-response association between physical activity and colon and pre- and postmenopausal breast cancer supported by identified biological mechanisms has been observed. The optimal permutation of type, intensity, duration, and frequency of physical activity across the lifespan is unclear, but it is gender, age, and site specific and supports moderate activity (>4.5 MET) more than light activities (<4.5 MET). The complicated nature of the physical activity variable, combined with lack of knowledge regarding possible biological mechanisms operating between physical activity and cancer, warrants further studies including controlled clinical randomized trials.

A case-control study of the relationship between the risk of colon cancer in men and exposures to occupational agents

BACKGROUND

We conducted a population-based case-control study in Montreal, Canada, to explore associations between hundreds of occupational circumstances and several cancer sites, including colon.

METHODS

We interviewed 497 male patients with a pathologically confirmed diagnosis of colon cancer, 1514 controls with cancers at other sites, and 533 population-based controls. Detailed job histories and relevant potential confounding variables were obtained, and the job histories were translated by a team of chemists and industrial hygienists into a history of occupational exposures.

RESULTS

We found that there was reasonable evidence of associations for men employed in nine industry groups (adjusted odds ranging from 1.1 to 1.6 per a 10-year increase in duration of employment), and in 12 job groups (OR varying from 1.1 to 1.7). In addition, we found evidence of increased risks by increasing level of exposures to 21 occupational agents, including polystyrene (OR for "substantial" exposure (OR(subst)) = 10.7), polyurethanes (OR(subst) = 8.4), coke dust (OR(subst) = 5.6), mineral oils (OR(subst) = 3.3), polyacrylates (OR(subst) = 2.8), cellulose nitrate (OR(subst) = 2.6), alkyds (OR(subst) = 2.5), inorganic insulation dust (OR(subst) = 2.3), plastic dusts (OR(subst) = 2.3), asbestos (OR(subst) = 2.1), mineral wool fibers (OR(subst) = 2.1), glass fibers (OR(subst) = 2.0), iron oxides (OR(subst) = 1.9), aliphatic ketones (OR(subst) = 1.9), benzene (OR(subst) = 1.9), xylene (OR(subst) = 1.9), inorganic acid solutions (OR(subst) = 1.8), waxes, polishes (OR(subst) = 1.8), mononuclear aromatic hydrocarbons (OR(subst) = 1.6), toluene (OR(subst) = 1.6), and diesel engine emissions (OR(subst) = 1.5). Not all of these effects are independent because some exposures occurred contemporaneously with others or because they referred to a group of substances.

CONCLUSIONS

We have uncovered a number of occupational associations with colon cancer. For most of these agents, there are no published data to support or refute our observations. As there are few accepted risk factors for colon cancer, we suggest that new occupational and toxicologic studies be undertaken focusing on the more prevalent substances reported herein.

Prostate cancer, benign prostatic hyperplasia and physical activity in Shanghai, China

BACKGROUND

Studies suggest that increased levels of physical activity might decrease the risk of prostate cancer. We ascertained lifetime measures of activity in a population-based case-control study of prostate cancer in Shanghai, China to investigate physical activity in a population where the incidence of prostate cancer is low but rising.

METHODS

In all, 238 men with prostate cancer, diagnosed 1993-1995, were identified through a rapid reporting system. A second group of 206 men with benign prostatic hyperplasia (BPH) was matched to prostate cancer cases, and 471 age-matched and population-based controls were identified from urban Shanghai. Through personal interviews, we ascertained all daily, occupational, and recreational activities at ages 20-29, ages 40-49, and in 1988 to generate hours spent sleeping, sitting, in moderate activity, and in vigorous activity. Time spent per week in different activities was converted to metabolic equivalents (MET-h) and energy expended.

RESULTS

Time spent in, MET-h of, and energy expended in physical activities were not consistently related to either prostate cancer or BPH when compared to controls. Few men reported regular vigorous activity. Occupational activity, based on an energy expenditure index using job titles, was suggestively associated with a decreased risk of BPH, but not associated with prostate cancer. Associations did not vary according to age or stage of prostate cancer at diagnosis.

CONCLUSIONS

Our results, based on regular physical activity, occupational activity, hours in activities, MET-h, and energy expended, did not support a protective role of physical activity in prostate cancer or BPH for men in a low-risk population.

Assessments of physical activity and cancer risk

The assessment of physical activity is one of the most important methodological issues in research into physical activity and cancer risk. A sedentary Western lifestyle has been observed to influence biological mechanisms promoting development of certain types of cancer. At present the totality of evidence supports a protective effect against cancers of the colon and probably the breast, while further data concerning carcinoma of other cancers are required. Thus, physical activity represents a powerful public health measure for reducing cancer risk. Studies of the association between physical activity and cancer risk have used a great variety of methods, but have most often included work and/or leisure time activity. Questionnaires are the method most often used and various components of physical activity such as type, frequency, intensity and lifetime physical activity have been recorded. However, the measurements used when assessing physical activity have been hampered by lack of accuracy as regards validity and reliability, missing information on the various components of physical activity and sparse information of lifetime exposure, and often no repeat assessments in cohort studies. Discrepancies between studies elaborating the association between physical activity and site-specific cancer risk may be explained through real differences or lack of information on the various components of physical activity (type, intensity, duration) and incomplete information about the cancer type studied (localization, histological type). The complicated nature of the variable physical activity, combined with incomplete understanding of the pathogenesis of most cancer and lack of knowledge regarding possible biological mechanisms operating between physical activity and cancer, warrants further studies. In these studies methodological improvements in measuring physical activity, combined with inclusion of physiological markers (heart rate, energy balance, hormonal levels, etc.) reflecting the variety of physical activities performed are of particular interest. Assessing biomarkers and intermediate steps for site-specific cancer risk may give us further insight into the relation between physical activity and cancer that will be of enormous interest for public health recommendations.

Cancer risk in laboratory workers: an emphasis on biological research

BACKGROUND

At the end of the 1980s, several cancer clusters were observed in biological research laboratories. Over time, biological research and the technologies used have been diverse and have involved a wide range of mutagenic or carcinogenic chemical, physical and biological agents.

METHODS

We reviewed 45 published studies on cancer risk among biological research personnel and workers in closely related fields, and numerous reports based on routinely collected data.

RESULTS

Biological research could be associated with an elevated risk for pancreatic cancer, brain tumors, and certain hemopathies. A common limitation of available studies was low statistical power and the absence or inaccuracy of data on individual past exposure.

CONCLUSIONS

Overall, this study suggests a low overall risk of cancer, albeit a higher risk may be suggested for cancers of the pancreas (risk ratios ranging from 0.5 to 6.3) and brain (0.7-9.4), and for non-Hodgkin's lymphoma (0.6-51.5). We suggest ways in which multiple past exposures could be assessed more precisely and emphasize a pressing need to take into account known confounders.

Physical activity and body weight: associations over ten years in the CARDIA study. Coronary Artery Risk Development in Young Adults

BACKGROUND

Hypothesis 1--sustained changes in physical activity are inversely related to changes in body weight. Hypothesis 2-those who attenuate weight gain because of a temporary increase in physical activity (PA) may maintain a lower body weight over time.

METHODS

Data were from the Coronary Artery Risk Development in Young Adults (CARDIA) Study, a cohort of black and white men and women, aged 18-30y at baseline, who attended up to five examinations over a 10y period (n=5,115 at baseline). Longitudinal associations between physical activity and body weight changes were assessed, adjusting for secular trend, age, clinic site, education, smoking, alcohol intake, parity, percentage energy intake from fat, and changes in these variables over time. For hypothesis 1, concurrent associations of physical activity and body weight changes were examined. For hypothesis 2, we explored whether weight gain attenuation associated with increased PA during the initial 2-3 y of follow-up was sustained over 5 y. The study 2 analyses were conducted with three separate 5y intervals: baseline to year 5 (n= 3,641), years 2-7 (n= 3,160), and years 5-10 (n= 2,617).

RESULTS

Hypothesis 1 -change in physical activity was inversely associated with change in body weight within all four race and sex sub-groups (P<0.005). The predicted weight change associated with change in physical activity was four to five times larger in participants who were overweight compared with those who were not were overweight at baseline. Hypothesis 2-an increase in physical activity during 2-3 y of follow-up was associated with an attenuation of weight gain that was sustained through 5y of follow-up whether or not the physical activity increase was maintained during the later years. This finding persisted whether the starting point for the 5y follow-up was year 2, year 5 or baseline (women only). Comparing participants who increased physical activity with those who decreased physical activity in the first 2-3 y of follow-up (eg by at least 2 h per week of stationary cycling for at least 6 months per year), the mean 5y weight gain attenuation ranged from 0.8 to 2.8 kg.

CONCLUSIONS

The results of these analyses support the need for public health messages for promoting increased physical activity for weight maintenance and attenuation of age-related weight gain, especially for higher weight sub-populations.

Physical activity, water intake and risk of colorectal cancer in Taiwan: a hospital-based case-control study

The age-adjusted mortality rates of colorectal cancer have been rising in Taiwan over the past 2 decades, and colorectal cancer is now the third leading cause of cancer mortality in the country. We conducted a hospital-based case-control study to clarify the nature of the association between physical activity, water intake and colorectal-cancer risk in Taiwan. A total of 163 subjects (aged 33-80 years) with histologically confirmed primary colorectal cancer and 163 hospital controls were enrolled during 1992. Dietary intake, physical activity and other lifestyle activities were assessed using a comprehensive food-frequency and lifestyle-activity questionnaire. Adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated using conditional logistic-regression analysis. A strong inverse dose-response relation between increased water intake and rectal cancer was found among men after adjustment for other risk factors (p for trend = 0.0005). The OR for rectal cancer among men in the highest tertile of water intake was 0.08 (95% CI, 0.02-0.35) compared with that among men in the lowest tertile (OR = 1). Similar but not significant trends were seen among women (p = 0.29). The OR for colon cancer among men with active leisure-time physical activity was 0.19 (95% CI, 0.05-0.77) times that among sedentary men (p for trend = 0.03). However, physical activity was not associated with colon-cancer risk among women (p = 0.48). No differences in the amount of water intake were found related to level of physical activity. These findings add to the evidence that leisure-time activity may reduce colon-cancer risk, not only in high-risk but also in low-risk populations, and support the potential beneficial effect of increased water intake in reducing colorectal-cancer risk.

Occupational physical activity and non-Hodgkin's lymphoma

PURPOSE

The purpose of this study was to evaluate the role of physical activity in the development of non-Hodgkin's lymphoma (NHL).

METHODS

Incident NHL cases and population-based controls were identified from three case-control studies conducted in four midwestern states: Iowa, Kansas, Minnesota, and Nebraska. A total of 1177 cases (993 men, 184 women) and 3625 controls (2918 men, 707 women) were interviewed. Usual occupation (all states) and lifetime occupational histories (Iowa and Minnesota only), obtained from interviews, were classified for energy expenditure (EE) and sitting time. Odds ratios (OR) and 95% confidence intervals were calculated comparing moderate and high activity levels with sedentary levels.

RESULTS

There was no evidence of an association between NHL and occupational physical activity measured either by EE or sitting time. Among men, the OR associated with usual occupation moderate and high EE were 1.1 and 1.0, respectively. For sitting time, the OR were also 1.1 and 1.0 for moderate and high activity, respectively. Among women, slight nonsignificant elevations in risk of NHL were observed among the high energy level and high activity sitting categories. The trends were not significant. There was no evidence of confounding or effect modification by vital status, hair dye use, or solvent exposure. Among subjects with lifetime occupational histories, there were no significant increases or trends for cumulative or average EE or sitting time. There was no association between occupational physical activity and NHL.

CONCLUSION

Research on nonoccupational physical activity, which in the U.S. is likely the more important component of daily activity than occupational activity, may still be warranted given the laboratory evidence linking physical activity and immune function, an important factor in the etiology of NHL.

Physical activity and the primary prevention of cancer

Evidence has been accumulating that suggests that physical activity may help reduce the risk of cancer. Physically active people have been shown to have a decreased rate of all-cancer mortality. The incidence of colon, breast, and perhaps prostate cancer are decreased in more active people when compared with their sedentary peers. Chronic physical activity may decrease tumor risk by its effect on natural immunity, antioxidant defenses, improved energy balance, hormonal changes, or by other unknown mechanisms.

Leisure-time physical activity, body size, and colon cancer in women. Nurses' Health Study Research Group

BACKGROUND

Physical inactivity and high body mass index (weight in kilograms divided by height in square meters) have been linked to increased risk of colon cancer. However, none of the few prospective studies in women has shown a statistically significant reduction in colon cancer incidence or mortality associated with increased leisure-time physical activity.

PURPOSE

In this prospective study, we asked whether leisure-time physical activity, body mass index, or body fat distribution could significantly influence the risk of colon cancer in women.

METHODS

The participants in this study were enrolled in the Nurses' Health Study, which began in 1976. Every 2 years, the women provided additional personal information and information on medical risk factors and major medical events. The time spent per week at a variety of leisure-time physical activities was determined, and the time spent at each activity was multiplied by its typical energy expenditure, expressed in terms of metabolic equivalents or METs. The resulting values for each woman were added to yield an MET-hours-per-week score. Reported diagnoses of colon cancer were confirmed by review of hospital records and pathology reports. Relative risks and associated 95% confidence intervals were calculated.

RESULTS

In multivariate analyses that included body mass index, women who expended more than 21 MET-hours per week on leisure-time physical activity had a relative risk of colon cancer of 0.54 (95% confidence interval [CI] = 0.33-0.90) in comparison with women who expended less than 2 MET-hours per week. Women who had a body mass index greater than 29 kg/m2 had a relative risk of colon cancer of 1.45 (95% CI = 1.02-2.07) in comparison with women who had a body mass index less than 21 kg/m2. A tendency toward higher colon cancer risk was observed for increasing waist-to-hip ratio (relative risk = 1.48 [95% CI = 0.88-2.49] for comparison of the highest quintile ratio [>0.833] to the lowest [<0.728]).

CONCLUSIONS AND IMPLICATIONS

The significant inverse association between leisure-time physical activity and incidence of colon cancer in women in this study is consistent with what has been found in men. Recommendations to increase physical activity and maintain lean body weight should receive greater emphasis as part of a feasible approach to the prevention of colon cancer.

Physical activity and risk of colorectal cancer in men and women

We examined the association between self-reported occupational and recreational physical activity and the subsequent risk of colorectal cancer in a population-based cohort in Norway. During a mean follow-up time of 16.3 years for males and 15.5 years for females, 236 and 99 colon cancers and 170 and 58 rectal cancers were observed in males and females, respectively, among 53,242 males and 28,274 females who attended the screening between 1972 and 1978. Physical activity at a level equivalent to walking or bicycling for at least four hours a week during leisure-time was associated with decreased risk of colon cancer among females when compared with the sedentary group (RR = 0.62, 95% CI 0.40-0.97). Reduced risk of colon cancer was particularly marked in the proximal colon (RR = 0.51, 95% CI 0.28-0.93). This effect was not observed for occupational physical activity alone, probably due to a narrow range of self-reported physical activity at work among females. However, by combining occupational and recreational physical activity we observed an inverse dose-response effect as increasing total activity significantly reduced colon cancer risk (P for trend = 0.04). Among males 45 years or older at entry to the study, an inverse dose-response effect was observed between total physical activity and colon cancer risk (P for trend = 0.04). We also found in males a stronger preventive effect for physical activity in the proximal as compared to distal colon. In addition, we found a borderline significant decrease in colon cancer risk for occupational physical activity in males 45 years or older when compared to the sedentary group (RR = 0.74, 95% CI 0.53-1.04). All results were adjusted for age, body mass index, serum cholesterol and geographic region. No association between physical activity and rectal cancer was observed in males or females. The protective effect of physical activity on colon cancer risk is discussed in regard to energy balance, dietary factors, age, social class, body mass index and gastrointestinal transit time.

Exercise and physical health: cancer and immune function

Over the last decade, there has been accumulating epidemiological data suggesting that exercise may decrease the risk of cancer, particularly colon cancer. However, exercise appears unrelated to rectal cancer risk. With regard to other cancers, because physical activity can alter levels of reproductive hormones, investigators have hypothesized that active individuals should experience decreased incidence of breast or prostate cancer. The better conducted studies suggest that exercise may reduce the risk of developing breast cancer. However, the epidemiological data on prostate cancer have been inconsistent. Meanwhile, data on other site-specific cancers have been sparse. An exciting and emerging body of research has suggested that exercise, at least in moderate amounts, can enhance the human immune system. Theoretically, then, this provides a further biological basis for expecting an inverse relationship between physical activity and cancer risk. However, the changes seen in immune function tend to be transient in nature; thus, the physiological significance with respect to cancer development is uncertain. Preliminary data also suggest that exercise may be beneficial for cancer patients by improving the quality of life and enhancing immune function. Although promising, this needs more careful research. Again, it is unclear whether the enhanced immune function is of any clinical significance in retarding the spread of cancer that has already developed. Finally, with regard to URTIs, moderate exercise appears to decrease the risk of this infection, although high-endurance exercise may increase the risk. This finding parallels the changes seen in the immune system in response to exercise and comes as no surprise, as the immune system also regulates susceptibility to infections.

United States non-Hodgkin's lymphoma surveillance by occupation 1984-1989: a twenty-four state death certificate study

Death certificates from 23,890 male and female non-Hodgkin's lymphoma (NHL) cases and 119,450 noncancer controls from 24 states for the period 1984-1989 were used to generate hypotheses regarding occupational associations. Cases were frequency matched by age, race, and gender with five controls per case. Odds ratios were calculated for 231 industries and 509 occupations. Significant associations were observed for a variety of white-collar professionals (i.e., real estate agents, secretaries, bookkeepers, teachers, postal employees, business agents, engineers, chemists, and medical professionals) and blue-collar occupations (i.e., firefighters, farm managers, aircraft mechanics, electronic repairers, mining machine operators, and crane and tower operators).

Occupation, physical activity, and risk of prostate cancer in Shanghai, People's Republic of China

Based on occupational data for all (n = 264) prostate cancer cases diagnosed during 1980-84 in urban Shanghai and on employment information from the 1982 census, standardized incidence ratios (SIR) were calculated for occupational groups classified by job type and physical activity level. White-collar workers (professionals, government officials, clerical workers, salespersons) had an elevated incidence of prostate cancer, although the excesses were not significant. In addition, when jobs were classified by time spent sitting or energy expenditure, men employed in occupations with low physical activity levels tended to have moderately elevated risks of prostate cancer. Findings from this study in an area with one of the world's lowest incidence rates of prostate cancer add to the accumulating evidence that jobs with a low level of physical activity are associated with an increased prostate-cancer risk.

Occupational physical activity and the incidence of cancer of the breast, corpus uteri, and ovary in Shanghai

BACKGROUND

A sedentary life style has been consistently associated with an increased risk of colon cancer, but the evidence for its association with breast and other gynecologic cancers is limited.

METHODS

Occupational information for 3783 incident patients with cancer (breast, 2736; corpus uteri, 452; and ovary, 595) whose disease was diagnosed during the period 1980-1984 was compared with 1982 census data on employment in Shanghai urban areas. The standardized incidence ratios (SIR) of these cancers were estimated for each occupational group classified by job titles and physical activity levels.

RESULTS

A significantly increased incidence of breast cancer was found among professionals (SIR = 158), government officials (SIR = 131), and clerical workers (SIR = 143); the incidence was reduced among service workers (SIR = 87) and craftsmen (SIR = 91). Occupational physical activity, as measured by sitting time and energy expenditure, was inversely related to breast cancer incidence, with SIR of 127-131 for inactive jobs (sedentary or low-energy expenditure) and 79-93 for active jobs (long periods of standing or high energy expenditure). Similar associations, although to a lesser extent, were also seen for cancer of the corpus uteri and ovary.

CONCLUSIONS

Women with low physical activity occupations had an increased incidence of cancer of the breast, corpus uteri, and ovary; the incidence was reduced among women with high-activity jobs. These findings were consistent with observations from earlier studies and provided further evidence that physical activity may lower the risk of these female hormone-dependent cancers.