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Workshop Report:
Physical Activity and Cancer Prevention
Loraine D Marrett, Beth Theis, Fredrick D Ashbury and an
Expert Panel
Volume 21, No. 4 - 2000
Abstract
A workshop to evaluate the evidence for the role of physical
activity in cancer prevention and to identify priorities
for action, particularly in relation to the primary prevention
of cancer, was held by Cancer Care Ontario in March 2000.
A review of the scientific evidence was commissioned and
an expert panel convened to consider the review report and
to make recommendations for public health, research and
intervention. The panel concluded that evidence was convincing
for the role of physical activity in preventing colon cancer;
probable for breast cancer; possible for prostate cancer
and insufficient for other sites. It recommended that physical
activity messages promoting at least 30-45 minutes of moderate
to vigorous activity on most days of the week be included
in primary prevention interventions for cancer.
The panel recommended that future research on physical activity
incorporate comprehensive assessments, including measures
of the multiple dimensions and types of physical activity;
biological mechanisms; and behavioural and population factors.
Cancer Care Ontario will incorporate physical activity messages
in its primary prevention programming around nutrition and
healthy body weight.
Key words: cancer etiology, cancer prevention, physical
activity
Introduction
Cancer is the second ranking cause of death in Ontario after
cardiovascular diseases. Unless cancer mortality rates decline
as significantly as have those for cardiovascular diseases,
it will likely become the leading cause of death within
a few decades.1
The National Cancer Institute of Canada estimates that 24,700
women and 25,200 men will be diagnosed with cancer and 11,200
women and 12,500 men will die from cancer in Ontario in
the year 2000.2 As the population grows and ages, and as
techniques to detect cancer in its early stages are more
systematically applied and improved, the number of people
diagnosed with cancer will continue to rise. Health Canada's
Cancer Bureau estimates that, if current trends continue,
the number of new cancer cases will increase by 40% by the
year 2010.3
The escalating cancer burden will increase the need for
treatment services and will have serious repercussions for
Ontario's health care system. A report by the Chief Medical
Officer of Health for the Province of Ontario stated that
some $1 billion was spent to treat persons with cancer in
1994 alone.4 Current costs are certainly higher because
of the greater number of cases, and because the costs of
some new chemotherapeutic agents are higher than those previously
used. A diagnosis of cancer has serious personal financial
consequences in the form of lost wages and the cost of medications
to offset the symptoms of the disease and its treatments.
Cancer control encompasses prevention, early detection,
treatment, supportive care, research and education. Although
there have been impressive advances in the treatment of
a few cancers, the four most common cancers (i.e., lung,
breast, colon and prostate) have to date proved extremely
difficult to treat effectively.5 To achieve important reductions
in cancer incidence, morbidity and mortality, greater emphasis
should be placed on prevention.6 Effective prevention initiatives
can decrease cancer incidence and mortality by 50% or more.7
Rates of cancers of the colon, breast and prostate vary
considerably around the world.8 For example, they are all
much more common in North America than in Asia. These patterns
and a large body of research support an important role for
lifestyle factors in the etiology of these, as well as many
other, types of cancer.
Identifying the role of physical
activity in cancer prevention
In the fall of 1999, the Division of Preventive Oncology
at Cancer Care Ontario (CCO) initiated a two-step process
to identify opportunities for research, policies and programs
relating to physical activity and the primary prevention
of cancer:
1. an expert in physical activity and cancer was commissioned
to review, evaluate and summarize the evidence; and
2. a workshop of experts was convened to consider the review
and to develop a consensus on the level of evidence and
priorities for action.
CCO is a provincial cancer control agency responsible for
the provision of many key cancer services and for overseeing
all aspects of cancer control in Ontario. CCO's Division
of Preventive Oncology is responsible for cancer prevention,
screening and surveillance, research in preventive oncology
and the Aboriginal cancer care program.
Review of the evidence for physical
activity and cancer prevention
As a first step, CCO engaged Dr. Christine Friedenreich
of the Alberta Cancer Board to conduct a systematic review
of the published literature on the etiologic role of physical
activity in relation to cancer.9 Dr. Friedenreich is a recognized
expert in this field and is also familiar with the operational
context of provincial cancer agencies. Her review included
an assessment of the frequency, intensity and duration of
physical activity associated with cancer risk reduction,
a summary of physical activity intervention research, and
her recommendations for further research and public health
actions.
Dr. Friedenreich evaluated the evidence relating physical
activity to a variety of cancers using an adaptation of
the criteria described in the report by the World Cancer
Research Fund/American Institute for Cancer Research (WCRF/AICR)
on nutrition and cancer prevention.10 In this report, "convincing"
evidence was defined as evidence that is conclusive; "probable"
means that the evidence is strong enough to conclude that
a causal relation was likely; "possible" means
that a causal relation may exist; and "insufficient"
means evidence is suggestive but too sparse to make a more
definitive judgement. Table 1 presents more detailed descriptions
of these levels of evidence.10
Dr. Friedenreich's report formed the basis of the workshop
discussions. It was, however, expected that the participating
experts' own knowledge of, and perspective on, both published
and ongoing research would amplify and perhaps alter Dr.
Friedenreich's conclusions and recommendations.
The workshop
The Physical Activity and Cancer Prevention workshop was
held in Toronto on March 24-25, 2000. An expert panel was
convened, comprising 11 scientists from academia, government
and cancer agencies in Canada, the United States and Norway.
Seven others were invited to attend as observers. See Appendix
1 for a list of participants, who represented the disciplines
of epidemiology, physical education and health, exercise
science and behavioural science.
Goal and objectives
The workshop's goal was to evaluate the evidence for the
role of physical activity in preventing cancer. Its objectives
were to achieve consensus on:
• whether the epidemiological, biologic and intervention
evidence on physical activity and cancer prevention is sufficiently
strong to provide clear direction for public health recommendations
and/or population interventions;
• recommendations for further action (knowledge gaps to
be addressed by research, types of research needed, public
health recommendations, and/or interventions) according
to cancer site (colorectal, breast, prostate, other sites);
and
• priority areas for further action.
Workshop materials, structure and agenda
Before the event, participants were sent the workshop agenda,
a list of attendees, a copy of the report prepared by Dr.
Friedenreich9 and published papers by two of the workshop
participants in the specific areas of biologic mechanisms11
and intervention research12. During the workshop itself,
selected additional information was distributed (e.g. Canadian
data on population levels of physical activity; a summary
of public health recommendations on physical activity from
a variety of organizations).
A questionnaire intended to identify the workshop participants'
perceptions of the state of the evidence (epidemiologic,
biologic and intervention research) and to help identify
public health issues and recommendations was also included
in their pre-workshop packages. Participants were asked
to submit their completed questionnaires to the facilitator
before the event so that the responses could be collated
for presentation early in the workshop. A copy of the pre-workshop
questionnaire is appended to this report (Appendix 2).
The workshop agenda called for a full day to review, discuss,
and begin to develop a consensus on the evidence. The second,
shorter day was reserved for completing the development
of the consensus and for developing public health recommendations
supported by that evidence.
Discussion of the evidence
Workshop participants were given an orientation to the needs
of CCO's Division of Preventive Oncology in the development
of strategies on physical activity and cancer prevention.
This was followed by the presentation of Dr. Friedenreich's
report and of the pre-workshop questionnaire results. Table
2 summarizes Dr. Friedenreich's review of the epidemiologic
literature and her evaluation of the strength of the evidence.
The presentations stimulated discussion on the quality of
the epidemiologic evidence for various cancer sites and
the potential for developing public health recommendations.
This led to more focused discussion on possible biologic
mechanisms for physical activity and cancer prevention and
exercise intervention research.
Workshop findings
Consensus on the evidence
The workshop participants largely endorsed the conclusions
of relationships between physical activity and cancer prevention
presented in Dr. Friedenreich's review. The consensus on
levels of evidence is outlined in Table 3.
TABLE 1
Description of levels of evidencea
Level of evidence Description
Convincing Epidemiological studies show consistent associations,
with little or no evidence to the contrary. There should
be a substantial number of acceptable studies (more than
20), preferably including prospective designs, conducted
in different population groups and controlled for possible
confounding factors. Exposure data should refer to the time
preceding the occurrence of cancer. Dose-response relationships
should be supportive of a causal relationship. Associations
should be biologically plausible. Laboratory evidence is
usually supportive.
Probable Epidemiological studies showing associations are
either not so consistent, with a number of studies not supporting
the association, or the number or type of studies is not
extensive enough to make a more definite judgment. Mechanistic
and laboratory evidence is usually supportive.
Possible Epidemiological studies are generally supportive,
but are limited in quantity, quality or consistency. There
may or may not be supportive mechanistic or laboratory evidence.
Alternatively, there are few or no epidemiological data,
but strongly supportive evidence from other disciplines.
Insufficient There are only a few studies, which are generally
consistent, but really do no more than hint at a possible
relationship. Often, more well-designed research is needed.
a Descriptions are from the World Cancer Research Fund/
American Institute for Cancer Research.10
TABLE 2
Summary of epidemiologic evidence on the association between
physical activity and cancera
Cancer site Consistency of evidence for a risk reduction
with increased physical activity levelsb Strength of risk
association Dose-responsec Time of life Biologic plausibility
Overall level of scientific evidenced
Colon 42 of 48 up to 70%
21 of 31 Activity throughout life?
Yes - several possible mechanisms Convincing
Breast 22 of 33 up to 70%
to no effect 13 of 21 Early life?
Adult life? Yes - several possible mechanisms Probable
Prostate 14 of 23 up to 50% to a 220%
9 of 17 Early life? Yes - some possible mechanisms Possible
Lung 7 of 10 60% to 30%
5 of 7 Unknown Unclear Insufficient
Testis 2 of 5 50% to no effect 2 of 4 Unknown Unclear Insufficient
Ovary 1 of 4 No effect 1 of 2 Unknown Yes - a few
possible mechanisms Insufficient
Endometrium 7 of 11 90% to
no effect 3 of 6 Unknown Yes - a few possible mechanisms
Insufficient
a Adapted from (9) and (13).
b Number of consistent studies out of total studies, both
case-control and cohort.
c Number of studies with dose-response out of total studies.
d See Table 1 for definitions.
TABLE 3
Consensus level of evidence for physical activity and cancer
prevention
Cancer site Level of evidencea
Colonb Convincing
Breast Probable
Prostate Possible
Endometrium, lung, testis Insufficient but promising for
further investigation
Other Insufficient
a See Table 1 for descriptions
b Many studies considered only colon and rectum cancers
combined. However, there were enough studies on colon cancer
alone to conclude that the evidence related to it, but not
to rectal cancer, was convincing.
Public health recommendations
Table 4 presents the consensus public health recommendations
for cancer risk reduction made to CCO by the workshop participants.
The participants acknowledged the challenges of drawing
definitive conclusions for public health recommendations
from the available evidence; the scientific literature does
not provide information on the details of level of physical
activity required to achieve optimal benefit (i.e. duration,
frequency, intensity, age). Despite these caveats, participants
felt there was sufficient evidence to make responsible recommendations
that were not inconsistent with those of other health bodies.
Some examples are displayed in Table 5.
Research recommendations
Participants felt that more research was needed for the
effects of physical activity on many cancer sites. All but
one of the recommendations presented in Table 6 apply to
studies of any cancer site. Because the evidence for the
benefit of physical activity in colon cancer prevention
is considered to be "convincing," participants
identified the need to conduct intervention research of
strategies to reduce colon cancer risk (see fifth-listed
recommendation). The first recommendation is bolded to indicate
that it represents a major overarching research consideration.
TABLE 4
Consensus public health recommendations on physical activity
and cancer risk reduction
• Physical activity recommendations should be included in
primary prevention interventions for cancer prevention.
• All messages for physical activity should be in the context
of reducing the risk of cancer rather than preventing cancer.
• In order to get cancer risk reduction benefits, physical
activity should comprise at least 30-45 minutes of moderate
to vigorous activity on most days of the week.
• Examples of moderate and vigorous physical activities
should be provided as part of messaging; these should include
activities appropriate to various age, sex and cultural
groups.
• Messaging should recognize the variation in maximal cardiorespiratory
capacity within the population. For example, since maximal
capacity declines, on average, with increasing age, the
upper end of the recommended activity level (i.e. 45 minutes
of vigorous exercise) is in general more appropriate for
youth and the lower end (i.e. 30 minutes of moderate exercise)
for the elderly. Recommended activity levels for those who
have been sedentary should initially be less than for those
who are already active.
• Physical activity messages can be linked to other risk
reduction messages, such as maintaining a healthy body weight.
• Physical activity should be encouraged at all ages.
• Advocacy is required for policies and environmental supports
for physical activity.
• A surveillance and measurement system should be implemented
for tracking population levels of physical activity.
TABLE 5
Summary of recommendations on physical activity from various
organizations
Source Recommendationa
Health Canada/Canadian Society for Exercise Physiology (Canada's
Physical Activity Guide)14 Get active your way, every day
- for life. Scientists say accumulate 60 minutes of physical
activity every day to stay healthy or improve your health.
As you progress to moderate activities you can cut down
to 30 minutes, 4 days a week. Add up your activities in
periods of at least 10 minutes each.
Start slowly . and build up.
Canadian Cancer Society (Seven Steps to Health)15 Be physically
active on a regular basis. This will also help you maintain
a healthy body weight.
Harvard Center for Cancer Prevention (7 ways to prevent
cancer)16 Get at least 30 minutes of physical activity every
day.
American Cancer Society (Guidelines on diet, nutrition and
cancer prevention)17 Be at least moderately active for 30
minutes or more on most days of the week.
U.S. Dept of Health and Human Services (Healthy People 2000)18
Objective:
Increase the proportion of people aged 6 and older who engage
regularly, preferably daily, in light to moderate physical
activity for at least 30 minutes per day to at least 30
percent.
U.S. Dept of Health and Human Services (Healthy
People 2010)19 Objectives:
Increase the proportion of adolescents who engage in vigorous
physical activity that promotes cardiorespiratory fitness
3 or more days per week for 20 or more minutes per occasion.
Increase the proportion of adults who engage regularly,
preferably daily, in moderate physical activity for at least
30 minutes per day.
International Union Against Cancer (UICC) (Statement on
diet, nutrition and cancer)20 Exercise to maintain weight.
World Cancer Research Fund/American Institute for Cancer
Research10 If occupational activity is low or moderate,
take an hour's brisk walk or similar exercise daily, and
also exercise vigorously for a total of at least one hour
a week.
a Quoted directly from the referenced documents.
TABLE 6
Summary of research recommendations on physical activity
and cancer prevention
• Physical activity assessment should be comprehensive and
include measures of
• type, frequency, duration and intensity of physical activity
in the relevant exposure periods (e.g. lifetime)
• leisure, occupational, household and transportation forms
of physical activity, in addition to other physical movements
that require considerable energy expenditure (e.g. fidgeting)
• biologic mechanisms (relevant to individual cancer sites
and across cancer sites) and
• behavioural and population (age, sex, socio-economic status,
and culture) factors
• Research should incorporate an assessment of the way physical
activity relates to other factors, including obesity, diet,
genetics and exposures such as use of medications, smoking
and alcohol.
• Studies should be conducted to establish biomarkers as
intermediate endpoints in the pathway for the relationship
between physical activity and cancer.
• Intervention research is needed for colon cancer to determine
the efficacy and effectiveness of various strategies to
reduce risk.
• Ongoing scans of published and current but unpublished
physical activity research projects should be conducted
to facilitate updating of assessment of evidence and public
health recommendations.
• Research is needed into environmental supports and policies
needed to facilitate physical activity intervention implementation
and adherence.
• Qualitative research should be conducted to establish
motivations to pursue a physically active lifestyle, with
special attention to age, sex, socio-economic status, and
culture.
• Methodological research is needed on recall bias and the
use of self-administered vs. interview-based data collection
protocols for physical activity assessment.
Discussion
As the number of women and men diagnosed with cancer in
Ontario (and throughout Canada) continues to rise, epidemiologic,
biologic, behavioural and intervention research studies
will be needed to facilitate public health interventions
for lifestyle factors that can be modified to reduce an
individual's risk of developing cancer. The process followed
in the workshop enabled a thorough discussion of the existing
evidence and afforded participants an opportunity to discuss
and identify recommendations and priorities for public health
and further research.
CCO has already incorporated this evidence assessment summary
into its "Blueprint for Cancer Prevention in Ontario,"
which was released in May 2000.21 The Blueprint identifies
tobacco control, promotion of healthy eating and physical
activity as the organization's priorities for cancer prevention.
CCO is currently developing a program of risk reduction
strategies based on nutrition, healthy body weight and physical
activity. The recommendations from this workshop will be
incorporated into a number of CCO's primary prevention initiatives.
Risk factor surveillance activities are also being designed
to track population trends in the recommended level of physical
activity, particularly in relation to new strategies or
programs.
The workshop recommendations should be widely disseminated.
They will be useful to agencies and organizations concerned
with physical activity and fitness, not necessarily in relation
to cancer, to further justify their efforts to promote the
health benefits of physical activity. They can also be used
as part of the strategic justification for funding proposals,
program development and policy advocacy efforts of CCO,
its partners and other agencies.
Acknowledgements
This workshop was supported by funding from the Prevention
Unit, Division of Preventive Oncology, Cancer Care Ontario.
We extend our thanks to the 11 scientists who made up the
expert panel, whose passion, graciousness and willingness
to share in the development of recommendations will assist
those working in cancer prevention for the province of Ontario.
We would also like to thank the observers for their time,
energy and insight and for providing a context for the ongoing
implementation of these proceedings.
For further information on the workshop and its recommendations,
please contact Dr. Loraine Marrett at Cancer Care Ontario.
References
1. Ontario Task Force on the Primary Prevention of Cancer.
Recommendations for the primary prevention of cancer. Toronto:
Ontario Ministry of Health, 1995.
2. National Cancer Institute of Canada. Canadian cancer
statistics 2000. Toronto: NCIC, 2000.
3. MacNeill I. Projections of mortality and hospital morbidity
for leading causes. Report to the Bureau of Operations,
Planning and Policy, Laboratory Centre for Disease Control,
Health Canada. April 2000.
4. Chief Medical Officer of Health. Progress against cancer.
Toronto: Ontario Ministry of Health, 1994.
5. Bailar JC, Gornik H. Cancer undefeated. N Engl J Med
1997;336:1569-74.
6. Miller AB. Canadian contributions to cancer control.
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7. Harvard Center for Cancer Prevention. Causes of human
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9. Friedenreich CM. Physical activity and cancer: review
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the Physical Activity and Cancer Prevention Workshop, Cancer
Care Ontario; 2000 March 24-25; Toronto, Canada.
10. World Cancer Research Fund/American Institute for Cancer
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activity and susceptibility to cancer: possible mechanisms.
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clinical trials in cancer prevention research: A call to
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13. Friedenreich CM. Physical activity and cancer prevention:
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Biomarkers Prev. In press 2001.
14. Health Canada. Canada's physical activity guide to healthy
active living. Ottawa, 1998; Cat. H39-429/1998.
15. Canadian Cancer Society. Seven Steps to Health. <www.cancer.ca/info/pubs/sevene1.htm>.
February 2000.
16. Harvard Center for Cancer Prevention. 7 ways to prevent
cancer. <www.hsph.harvard.edu/Organizations/
Canprevent/7ways.htm>.
January 2000.
17. American Cancer Society. Guidelines on diet, nutrition
and cancer prevention. May 1999.
18. U.S. Department of Health and Human Services. Healthy
People 2000: National health promotion and disease prevention
objectives. Washington, DC: U.S. Department of Health and
Human Services, Public Health Service, 1990. DHHS Pub No.
(PHS) 91-50212.
19. U.S. Department of Health and Human Services. Healthy
People 2010. <www.health.gov/healthypeople/Document/HTML/uih/
uih_4.htm#physactiv>. January 2000.
20. International Union against Cancer. UICC statement on
diet, nutrition and cancer.
<www.uicc.org/nutrition/nutristate.shtml>. July 1999.
21. Cancer Care Ontario. An ounce of prevention: Ontario's
cancer prevention blueprint 2000. Toronto: Division of Preventive
Oncology, Cancer Care Ontario, May 2000. <www.cancercare.on.ca/reports/blueprint/cover.html>.
Author References
Loraine D Marrett, Division of Preventive Oncology, Cancer
Care Ontario; and Department of Public Health Sciences,
University of Toronto
Beth Theis, Division of Preventive Oncology, Cancer Care
Ontario
Frederick D Ashbury, PICEPS Consultants, Inc.; Department
of Oncology, McGill University; Faculty of Nursing, University
of Manitoba; and Centre for Health Promotion, University
of Toronto
http://www.phac-aspc.gc.ca/
publicat/cdic-mcc/21-4/a_e.html
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