25 Jun THE RELATIONSHIP BETWEEN PHYSICAL ACTIVITY AND BREAST CANCER
Question
Rubric for Essay 1 (total points = 200) 3-5 pages 1.5 spaced
Description of the article (25) (X3 articles = 75) _____
Population (5) _____ _____ _____ = _____
PA assessment (5) _____ _____ _____ = _____
Cancer assessment (5) _____ _____ _____ = _____
Mentions strength of the relationship (5) _____ _____ _____ = _____
Confidence in results (5) _____ _____ _____ = _____
Analysis (10) (X3 articles=30) _____
Refer to the 7 aspects of causality
Integration (20) _____
Pattern of effects across the studies (10) _____
Strengths/weaknesses of studies (10) _____
Overall assessment (30) _____
Requirements for causality – do these studies meet? (10) _____
Refers to at least 2 of the 7 basis of causality for each
Where are they lacking? (10) _____
Implications for future research (10) _____
Writing (45) _____
Format (5) _____
1.5 spacing
adequate length
spelling and grammar
Clarity of presentation and organization (15) _____
Thoughts well-organized and logical (15) _____
Correct in-text citations (APA format) and works cited page (10) _____
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1. Description and Analysis
“A Prospective Study of Recreational Physical Activity and Breast Cancer Risk”
Rockhill, 1999
First, population was female registered nurses aged between 30 to 35 in 1976. The Nurses’
Health Study (NHS) is a prospective cohort study; 121,701 females were enrolled by responding
to a mailed questionnaire about their medical histories, lifestyle, and more through every 2 years.
Here, voluntary response bias exists, because individuals could choose whether they want to
participate in the study or not.
Second, in the PA assessment questionnaire, women were asked about their weekly physical
activity patterns. The 1980 Questionnaire surveyed average number of hours spent each week in
the previous year for moderate or vigorous recreational activities. In this PA assessment by selfreported survey, most participants responded with overestimations of their physical activity
levels in terms of intensity and hours during the whole 16-year period.
Third, in the cancer assessment questionnaire, women were asked if they had been diagnosed
with breast cancer in the previous 2 years. PA within MET values (over 6.0) could make the
validity of the data. The reference group was same as the PA assessment group. This cancer
assessment has an error with sample bias due to their job. Nurses could diagnose themselves,
would obtain hospital records and pathology reports.
Forth, strength of relationship suggested moderate inverse relationship between higher
moderate/vigorous PA levels and breast cancer risk, especially when cumulative average was
used. Both moderate and vigorous PA activity results in same advantage regardless of intensity of
the activity.
Lastly, confidence in results, study was multivariable and consisted of large sample size and
cohort study design established time precedence. (121,701). Higher levels of moderate or
vigorous activity were modestly associated with reduced breast cancer risk. More active women
tend to be leaner women. However, less consistent dose response evidence in BMI, but most
effective for lower BMI women in class cancer materials. Furthermore, in subsample for
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correcting self-reported bias in BMI, the subsample was too small (118, 140 participants)
compared with total participants.
Rockhill study showed the elements of causality; moderate dose-response, strong study
design, time precedence. Rockhill failed to demonstrate Reversibility, Biological plausibility and
Strength of relative risk. Rochhill did not research about adolescent period activity status. If
nurses were vigorous at active at adolescent period and inactive at adult period, they have more
advantage of breast cancer incidence than who were not inactive at adolescent period and active
at adult period. Consistency in different population has an error with sample bias due to their job.
Nurses could diagnose themselves, would obtain hospital records and pathology reports.
Moreover, subsample for BMI accuracy is so small (only 100 people subsample). In Dose
response, the article indicates that there is yet to be consensus on how to quantify physical
activity because of self-reported bias. This indicates that there is no consensus on dosage levels
and extent of physical intervention. Strong Study design is also ambiguous. Although this
research had a huge sample size of 12701 members and long-period investigation for 16 years,
but sample (nurse) was wrong.
“Relation Between Intensity of physical activity and breast cancer risk of reduction”
Friedenreich, 2000
First, testing population was residents of Alberta, 80 years old or younger, based on their
English proficiency and ability to complete in-person interview. There were selection bias in
region and large range age. This limited area was a problem, as the people of this region had
longer life expectancy compared with other regions. Also, wide range of age could lead to
unclear result of this research. 1233 (every case had breast cancer) were eligible and 1237 (no
cancer). The overall response rate for the control was 56.5%, which could be an issue for
determination of a result. Although researcher mentioned a limitation of large population,
researcher did not catch 43.5% population so that the result would be huge different. The inperson interviewing method most likely people who are immobile or have lower levels of
education. For example, you are more likely to go for the “interview” if you have a higher
education level.
Secondly, PA Assessment, the interview in August 1995 contained extensive questions of
health history, BMI, ethnicity, and educational level. However, sample was mainly Caucasian so
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that researcher may have a limitation of result. Moreover, Questionnaires about lifetime physical
activity were also assessed with the help of recall calendars. MET values were assigned to
activities based off intensity. Furthermore, interviewee could overestimate themselves, even with
the help of recall calendars, a person will still overestimate their physical activity to fit patterns
or to explain stereotypes.
Third, cancer assessment, those involved with the case were chosen because they were in the
Alberta Cancer Registry. There is 95% accuracy that each patient had breast cancer. There is
some limitation conclusion of decreased risk of breast cancer for postmenopausal. The reason of
household activities duration might decrease risk of breast cancer, but postmenopausal women
already had an advantage of reduction (30~35%) of breast cancer.
Forth, strength of relationship, moderate-intensity activity was associated with the greatest
risk reduction than vigorous-intensity activity and recreational activity. The effect of physical
activity on breast cancer risk is more clearly demonstrated when physical activity data are
expressed as frequency and duration of the physical activity performed at any level of intensity.
This research also gave Stronger association with assigned intensity data (MET’s) rather than
self-reported.
Lastly, confidence in results, Interviewers knew identities of sample and control. No matter
what, there will always be a slight bias. This study designed for a woman’s lifetime, but data
only was collected between Augusts 1995-1997.
Friedenreich study showed the elements of causality; Dose-response, Biological plausibility,
and Strength of relative risk. Friedenreich failed to demonstrate Reversibility, Consistency across
populations and Strong study design. In Strength of relative risk point, the study indicated that
risk reductions are mainly attained when the frequency of physical activity as well as its duration
is well modeled. In dose response, the study does indicate direct response to increased dosage
within duration and frequency. Only moderate interventions by women in terms of physical
activities end up generating positive results. In regards to consistency, it is clear that there is no
evidence that the outcome of the study could be repeated in people of other races or culture. For
instance, this case has solely relied on married Caucasian. These individuals in the study have
same personal and reproductive histories. This indicates that the outcome of this study cannot
thus be generalized on the entire population. In strong study design, there is some issue. Those
involved with the case were chosen and Interviewers knew who was a control and who was a
case. No matter what, there will always be a slight bias. This study designed for a woman’s
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lifetime, but data only was collected between Augusts 1995-1997.
“Physical Activity And The Risk of Breast Cancer” Thune. 1997
First, population is 25,624 women, 20-54 years of age at entry between the years 1974-1978
and 1977-1983 and all from Norway. These women had not been given cancer diagnosis so that
there is no comparison group who had given breast cancer. The reference group is that who are
sedentary.
Second, PA Assessment, Self-reported categories of physical activity during leisure hours and
work hours was graded 1(sedentary life) to 4(vigorous activity life). Self-reported bias could be
exist and responders would overestimate their physical activity hours.
Third, cancer assessment, Women were observed for the development of breast cancer from
entry into the study to the date of diagnosis of any cancer, time of death, or end of follow up.
Forth, strength of relationship, a 52% reduction in risk was observed among women who
reported doing heavy physical labor. Weak relationship between level of physical activity and
postmenopausal risk of breast cancer. Moreover, the researcher ignored dietary factors. Inverse
association of level of activity at work and risk of breast cancer was pronounced for
premenopausal women. They insisted that lower BMI was related to lower breast cancer.
However, less consistent dose response evidence in BMI. Actually, in table 5, researcher did not
mention about over 30 BMI. In class material, over 30 BMI has a lower breast cancer compared
with under 30 BMI.
Lastly, confidence in results, precise physical activity levels is difficult in a population-based
cohort. Accuracy of levels of leisure-time activity could be misleading. Population-selection
approach and high participation rate reduced selection bias, but that would be selection bias
because researcher did not analyzed high BMI population.
Biological plausibility is another element that is used in the assessment. For instance, it helps
in assessing whether there is a relation between breast cancer and issues such as obesity and
hypertension. This is based on the understanding that physical activity affects hormone levels
and consequently, it is likely to influence the level of occurrence of hormones or not. Strength in
relative risk is high, 52% of the reduction in breast cancer among women who engage in physical
activity was recorded and also dose-response is exist. The more the physical activity the
participants engage in the lesser the risk. The study indicated that continued engagement in
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sports ended up protecting women from breast cancer. The impact of such intervention is thus
highly influenced by its frequency. However, there is some issue about weak observation in
physical activity and postmenopausal risk of breast cancer. Consistency in different population
aspect, it would be different at other region because this data was collected only Norway.
Moreover, Self-reported bias could be exist and responders would be overestimated their
physical activity hours. In strong study design, less consistent dose response evidence in BMI.
Actually, in table 5, researcher did not mention about over 30 BMI. In class material, over 30
BMI has a lower breast cancer compared with under 30 BMI.
3. Integration
The above study indicates that physical activity should be a preventive approach to
cancer management and not a curative one. In pattern of effect across the studies, excess physical
activity does not increase prevention but also moderated physical activity may prevent breast
cancer. Thus, Dose-response is moderate in breast cancer. While the studies (Rockhill, Thune)
have identified inverse relationship between BMI and breast cancer prevention, breast cancer has
less consistent in BMI. Their weakness of studies lies in their inability to identify how much
physical activity reduces the risk of cancer because of self-reported bias (Rockhill, Thune). From
the three articles, they had a sample bias (Rockhill: nurse and small subsample for BMI article
Friedenreich: wide range of age and limited area, Thune: all from Norway). Moreover, they
ignored biological plausibility factor of menopausal status (Friedenreich) In spite of this, the
authors do recognize the gap that exists when it comes to the determination as whether physical
activity contributes to prevention of breast cancer.
4 Overall assessments
All the above studies do not explain causality fully. But clearly, Dose-response is exist
between physical activity and breast cancer. However, it is not clear in all the three articles as to
why physical activity would prevent breast cancer because of sample, self-reported, biological
factor and BMI bias. This could be because the studies are mainly exploratory, laying a
foundation for further research. Future research should thus be carried out in regards to causality.
One of the key strengths of any research work is to identify the cause of particular phenomena
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before a solution on the same is sought. These studies are thus shallow and should be backed up
with further studies.
Of the studied, individuals, it was evident that those that often engaged in PA were less
prone to breast cancer as compared to those who hardly engage in such activities. This is more so
the case with younger pre-menopausal women have more advantage than post-menopausal
women and vice versa. The level of activity that individuals engaged in their leisure time as well
as during work ended up reducing their risk of getting breast cancer. Repeated assessments
indicated the needs for continued physical activity, although the right frequency of such physical
activity is yet to be determined. Further research should thus be carried out on the topic related to
menopausal status, intensity of PA, BMI status, and frequency and duration, and lastly MET
evaluation rather than self-reported. These questions must be identified and classified within
sample.
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References
Rockhill, et al (1999).A prospective study of recreational physical activity and breast cancer
risk. Arch Intern Med, 159(1), 2290-2296
Friedenreich, C., Courneya, K.S., & Bryant, H.E. (2000).Relation Between Intensity of physical
activity and breast cancer risk of reduction. New York: American College of Sports
Medicine
Thune, I. et al. (2012). Physical activity and the risk of breast cancer.The England Journal of
Medicine, 36(18), 1269-127
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