My notes on "Cancer Rates of Vegetarians and Vegans – Summary of Prospective Cohort Studies, 1960–2014".

1. CANCER RATES OF
VEGETARIANS AND
VEGANS
Summary of Prospective Cohort Studies, 1960–2014
Notes by Jussi Riekki

2. World Cancer Research
Fund (WCRF) Report, 2007
”People who eat various forms of vegetarian diets
are at low risk of some diseases including some
cancers, although it is not easy to separate out
these benefits of the diets from other aspects of
their ways of life, such as not smoking, drinking
little if any alcohol, and so forth. … Red or
processed meats are convincing or probable
causes of some cancers.”
2
(WCRF, 2007)

3. Personal Recommendations,
WCRF, 2007
• Eat mostly foods of plant origin:
Eat at least five portions/servings
(at least 400 g or 14 oz) of a
variety of non-starchy vegetables
and of fruits every day. Eat
relatively unprocessed cereals
(grains) and/or pulses (legumes)
with every meal. Limit refined
starchy foods.
• Limit intake of red meat and
avoid processed meat: People
who eat red meat should
consume less than 500 g (18 oz)
a week, and very little if any
processed meat.
3
(WCRF, 2007. More on recommendations, see p.18–22)

4. Do Vegetarians and
Vegans Have A Lower
Risk of Cancer?
4
Lets take a look at the research done on cancer mortality
and incidence rates of vegetarians. But first...

5. Hierarchy of Evidence
(Micha & Mozaffarian, 2010)
Randomized Trials of Risk Factors!
!
!
Retrospective Case-Control Studies of Disease Outcomes!
!
!
Animal Studies, Ecologic Studies, Prevalence Reports!
!
!
Case series / reports
Randomized Trials!
and Prospective Cohorts!
of Disease Outcomes
Our Focus is on!
Prospective Cohorts of!
Disease Outcomes
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6. Different Diets, Similar Lifestyles.
Prospective Cohort Studies, 1960–2014
Study Country Years Key et al. 1999 Huang et al. 2012
Adventist Mortality USA 1960–65 Included Included
Adventist Health USA 1974–97 Included Included
Health Food
Shoppers
UK 1976–88 Included Included
Oxford Vegetarian UK 1981–2000 Included Included
Heidelberg Germany 1978–99 Included Included
EPIC-Oxford UK 1993– Not included Included
Adventist Health
Study 2
USA 2002– Not included Not included
Meta-Analyses
6

7. Key et al. 1999
Mortality in vegetarians and nonvegetarians: detailed findings from a
collaborative analysis of 5 prospective studies. American Journal of Clinical
Nutrition. 1999 Sep;70(3 Suppl):516S-524S.
7

8. 1999 Meta-Analysis
Findings
There was no significant differences between vegetarians
and non-vegetarians in mortality from any cancer.
Cancer
Stomach Colorectal Lung Breast Prostate
Vegetarians 1.02 (0.64, 1.62) 0.99 (0.77, 1.27) 0.84 (0.59, 1.18) 0.95 (0.55, 1.63) 0.91 (0.60, 1.39)
Statistically significant and borderline significant findings are in red.
(Key et al. 1999) 8

9. Cancer Mortality Rates in Individual
Studies, Key et al. 1999
There were only 2 cases of lung cancer in Heidelberg. Higher breast cancer
mortality in Health Food Shoppers remains to be explained (Key et al. 1999).
Cancer
Stomach Colorectal Lung Breast Prostate
Adventist
Mortality
0.64 (0.30, 1.36) 1.37 (0.73, 2.56) 0.59 (0.10, 3.28) 0.65 (0.28, 1.52) 1.41 (0.49, 4.04)
Health Food
Shoppers
1.23 (0.62, 2.47) 0.90 (0.58, 1.39) 1.13 (0.67, 1.92) 1.74 (1.11, 2.72) 1.31 (0.65, 2.66)
Adventist Health 1.58 (0.68, 3.70) 1.01 (0.66, 1.56) 0.69 (0.37, 1.27) 0.52 (0.27, 0.97) 0.79 (0.44, 1.41)
Heidelberg 2.66 (0.32, 21.7) 0.35 (0.06, 2.11) - 1.09 (0.18, 6.67) 1.67 (0.14, 19.6)
Oxford Vegetarian 0.46 (0.11, 1.85) 0.94 (0.49, 1.80) 0.66 (0.31, 1.37) 1.10 (0.57, 2.12) 0.42 (0.16, 1.09)
9

10. Cancer Mortality Rates by Dietary Pattern,
Key et al. 1999
”…exclusion of data from the Health Food Shoppers Study in this analysis
tended to lower the death rate ratio in the vegetarian groups compared with
the nonvegetarian groups.” (Key et al. 1999)
Cancer
Stomach Colorectal Lung Breast Prostate
Semi 0.36 (0.11, 1.18) 1.14 (0.72, 1.82) 0.69 (0.39, 1.22) 0.97 (0.56, 1.71) 1.06 (0.60, 1.89)
Pesco 0.86 (0.20, 3.74) 1.00 (0.42, 2.38) 1.04 (0.41, 2.64) 1.50 (0.74, 3.04) 1.25 (0.30, 5.22)
Lacto-ovo 0.71 (0.42, 1.21) 1.10 (0.79, 1.54) 0.62 (0.38, 1.00) 0.75 (0.49, 1.14) 0.75 (0.47, 1.21)
Vegan 2.18 (0.43, 11.2) 0.83 (0.11, 6.17) 2.79 (0.39, 20.0) – –
10

11. Huang et al. 2012
Cardiovascular disease mortality and cancer incidence in vegetarians: a meta-
analysis and systematic review. Annals of Nutrition and Metabolism. 2012;60(4):
233-40.
11

12. Cancer Incidence in Huang et al. 2012
(Huang et al. 2012)
The overall cancer incidence was significantly lower (0.82
[0.67, 0.97]) in vegetarians compared to meat-eaters.
12

13. A Closer Look on
Adventist Health Study 2
and EPIC-Oxford
… and cancer incidence in vegans.
13

14. Key Findings in Adventist
Health Study 2
• In conclusion, this study suggests that vegan diets may be
associated with a decrease in the incidence of all cancers
combined, and specifically the risk of female-specific
cancers when compared with non-vegetarians.
• Vegetarians had a 24% lower risk of gastrointestinal
cancer (HR 0.76; 95%CI: 0.63–0.90). In addition, vegan
women experienced 34% fewer female-specific cancers.
• When adding BMI into the multivariate models most of the
statistically relative risks remain significant, but move
slightly toward the null suggesting that BMI may be one
mediator of the dietary effects.
14
(Tantamango-Bartley et al. 2013)

15. Cancer Incidence Rate by Dietary Pattern
and Cancer Type, AHS-2
Cancer
Overall Gastrointestinal Respiratory Urinary Male spesific Female spesific
Semi 0.98 (0.83, 1.18) 0.73 (0.48, 1.13) 0.73 (0.37, 1.47) 1.56 (0.93, 2.61) 1.11 (0.75, 1.64) 1.02 (0.74, 1.40)
Pesco 0.89 (0.77, 1.03) 0.78 (0.56, 1.07) 0.53 (0.28, 1.03) 0.88 (0.51, 1.52) 0.91 (0.66, 1.25) 0.88 (0.69, 1.12)
Lacto-ovo 0.95 (0.86, 1.04) 0.75 (0.60, 0.93) 0.91 (0.63, 1.33) 1.08 (0.76, 1.54) 0.94 (0.77, 1.15) 1.01 (0.85, 1.19)
Vegan 0.86 (0.73, 1.00) 0.78 (0.54, 1.13) 0.62 (0.30, 1.28) 1.57 (0.96, 2.57) 0.81 (0.57, 1.16) 0.66 (0.47, 0.92)
Vegetarians
combined
0.92 (0.85, 1.00) 0.76 (0.63, 0.90) 0.77 (0.55, 1.06) 1.17 (0.87, 1.57) 0.93 (0.42, 2.06) 0.93 (0.81, 1.07)
(Tantamango-Bartley et al. 2013) 15
Adjusted by race, family history of cancer, BMI, education, smoking, alcohol, age at menarche,
pregnancies, breastfeeding, oral contraceptives, hormone replacement therapy, and menopause status.

16. Overall Cancer Incidence Rate of
Vegetarian Men and Women, AHS-2
Adjusted by race, family history of cancer, BMI, education, smoking, alcohol, age at menarche,
pregnancies, breastfeeding, oral contraceptives, hormone replacement therapy, and menopause status.
*Adjusted only by age.
Men and Women Men Women Men and women*
Semi 0.98 (0.83, 1.18) 1.11 (0.85, 1.45) 0.92 (0.73, 1.16) 1.00 (0.86, 1.17)
Pesco 0.89 (0.77, 1.03) 0.88 (0.71, 1.09) 0.90 (0.74, 1.09) 0.84 (0.74, 0.96)
Lacto-ovo 0.95 (0.86, 1.04) 0.92 (0.80, 1.06) 0.96 (0.85, 1.08) 0.94 (0.86, 1.02)
Vegan 0.86 (0.73, 1.00) 0.81 (0.64, 1.02) 0.91 (0.75, 1.11) 0.83 (0.71, 0.97)
Vegetarians combined 0.92 (0.85, 1.00) 0.92 (0.81, 1.03) 0.93 (0.84, 1.03) 0.91 (0.85, 0.98)
(Tantamango-Bartley et al. 2013) 16

17. Key Findings in EPIC-Oxford
• The overall cancer incidence in this study was
lower than the national average.
• The risk of all malignant neoplasms was non-
significantly lower in vegetarians than in non-
vegetarians (0.93; 95% CI: 0.83, 1.04).
• The incidence of colorectal cancer was
paradoxically 49% higher in vegetarians than in
meat eaters (1.49; 95% CI: 1.09, 2.03).
17
(Key et al. 2009)

18. Cancer Incidence Rate in EPIC-Oxford
Adjusted by age, gender and smoking. See next slide for further information
about the ”paradoxical” colorectal cancer incidence (Key et al. 2009).
Cancer
Colorectal Breast Prostate Ovarian Lung
All malignant
neoplasms
Vegetarians
combined
1.49 (1.09,
2.03)
0.94 (0.77,
1.13)
0.90 (0.61,
1.33)
0.85 (0.49,
1.46)
1.23 (0.69,
2.17)
0.93 (0.83,
1.04)
Pesco
0.64 (0.37,
1.10)
1.02 (0.81,
1.29)
0.88 (0.49,
1.57)
0.43 (0.18,
1.01)
0.23 (0.06,
0.95)
0.83 (0.71,
0.96)
Lacto-ovo or
vegan
1.39 (1.01,
1.91)
0.94 (0.77,
1.15)
0.89 (0.60,
1.32)
0.73 (0.42,
1.28)
1.08 (0.61,
1.91)
0.89 (0.80,
1.00)
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19. Colorectal Cancer ”Paradox”
A Reverse Causation?—Gilsing et al. 2013 found
that within the Netherlands Cohort Study 75% of
vegetarians with a prevalent cancer at baseline had
changed to this diet after diagnosis.
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”Our observation that the incidence of colorectal cancer is higher
among vegetarians than among meat eaters in the EPIC-Oxford
study is surprising; this difference might be partly due to chance
and speculatively might be related to other dietary differences
between the groups.” —Key et al. 2009

20. My Conclusions
✓ Vegetarian dietary pattern is associated with a lower
overall cancer incidence—18% in 2012 meta-analysis
—but not mortality.!
✓ In AHS-2, vegetarians had a 24% lower risk of
gastrointestinal cancer. No significant differences in
other cancer types between meat-eaters and
vegetarians were found.!
✓ Vegans don’t have exceptionally high nor low cancer
incidence rates, although vegan diet seems to confer
lower risk for female-specific cancer.
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