obesity and cancer: the link. the panel’s recommendation
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Obesity and Cancer: The Link
The Panel’s Recommendation
Obesity and Cancer: The Evidence
• AICR/WCRF is continually updating the evidence
• Breast cancer update released in 2009
- 2007 expert report based on 873 studies
- Update included additional 81 studies
- Findings strengthened previous conclusions that women can reduce risk by maintaining low body fat, being physically active, drinking no alcohol and breastfeeding their children.
• Updates of colon and prostate cancer are now underway.
Obesity and Cancer: Mechanisms
• Adipose tissue is an active endocrine organ
• Mechanisms by which adipose tissue may influence cancer risk
- Production of sex steroid hormones (e.g., estrogen, androgen)
- Effects on insulin sensitivity and production of insulin-like growth factors
- Actions on other hormones in adipose tissue (e.g., leptin, adiponectin)
- Increases in oxidative stress and chronic low-grade inflammation that affect the body’s immune response
Developing the Preventability Estimates
• Several sources of data were used:– Current estimates of cancer incidence in the US and the actual number of cancer
cancers
– Survey data on the prevalence of rates of different levels of overweight/obesity in the US population
– Estimates of the risk of developing specific cancers associated with these levels of overweight, based on key studies in the literature
• These data are combined to compute a population attributable fraction (PAF), and the estimated numbers of preventable cancers
Obesity and Cancer: Conclusions
• A healthy diet can help sustain a healthy weight and lower risk of cancers
• regular physical activity protects against the buildup of excess body fat and against cancer, independently
Lifestyle Habits and Breast Cancer Survival
• Higher BMI and lower physical activity are associated with a reduced risk of breast and colon cancer specific survival.
• Current cancer therapies do not address the association of obesity and sedentary lifestyle effects on prognosis.
• Obesity and physical inactivity are common before and after a breast cancer diagnosis.
Mortality from Cancer According to BMI for U.S. Women in the Cancer Prevention Study II
Calle, E. et al. N Engl J Med 2003;348:1625-1638
Weight and Survival in Early-Stage Breast Cancer
BMI (kg/m2)
Es
tim
ate
d R
ela
tiv
e R
isk
of
Ad
ver
se E
ven
t
20 30 40 50
05
1015
25 35 45 55
Distant Recurrence, p=0.0005
Death, p=0.0007
Goodwin et al, JCO 2002
Nurses’ Health Study: Physical activity after breast cancer diagnosis
0
0.10.2
0.30.4
0.5
0.60.7
0.80.9
1
Recurrence BRCA Death Total Death
<33-8.99-14.915-23.9
MET-Hrs/week
*p=0.05, # p<0.004
MET-hr/wk
Holmes M et al JAMA 2005
P = .05
HR
P= .004 P = .003
The HEAL Study: Physical Activity after Diagnosis
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
BC Death Total Death
0
>0 - 9
9+
Haz
ard
Rat
io f
or
Dea
th MET-hr/wk
Irwin ML et al JCO, 2008.
P = .04P = .46
Benefits of Increasing Post-Diagnosis PA
• Need to encourage cancer survivors to maintain (if Need to encourage cancer survivors to maintain (if active prior to diagnosis) or increase physical activity active prior to diagnosis) or increase physical activity after diagnosis.after diagnosis.
• Physical activity is associated with numerous benefitsPhysical activity is associated with numerous benefits– Decreasing adverse side effects of surgery and treatmentDecreasing adverse side effects of surgery and treatment
– Improving quality of life and fatigueImproving quality of life and fatigue
– Improving fitness, functional capacity, and Improving fitness, functional capacity, and body composition body composition
– Decreasing serum hormones and growthDecreasing serum hormones and growth
factorsfactors
– Improving cancer-specific survival and Improving cancer-specific survival and all cause survival all cause survival
9490
87
52 51
46 46
38
0
10
20
30
40
50
60
70
80
90
100
% o
f Am
eric
ans
wh
o B
elie
ve it
to
be
a C
ause
of
Can
cer
2009 Cancer Risk Awareness
2009 Cancer Risk Awareness
35
45 4446
51
0
10
20
30
40
50
60
70
80
90
100
2001 2003 2005 2007 2009
OBESITYOBESITY
Percentage of Americans who
Believe it to be a Cause of Cancer
Percentage of Americans who
Believe it to be a Cause of Cancer
YearYear
0%
5%
10%
15%
20%
25%
30%
35%
40%
Cancer Heart Attack Adult Diabetes Stroke
0%
5%
10%
15%
20%
25%
30%
35%
40%
Cancer Heart Attack Adult Diabetes Stroke
Percentage of Americans Who Rate It Their #1 Health Concern
Percentage of Americans Who Rate It Their #1 Health Concern
Percentage of Americans Who Consider It “Highly Preventable”
Percentage of Americans Who Consider It “Highly Preventable”