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Cancer Rates of Vegetarians and Vegans – Summary of Prospective Cohort Studies, 1960–2014

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Cancer Rates of Vegetarians and Vegans – Summary of Prospective Cohort Studies, 1960–2014

  1. 1. CANCER RATES OF VEGETARIANS AND VEGANS Summary of Prospective Cohort Studies, 1960–2014 Notes by Jussi Riekki
  2. 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. 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. 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. 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 5
  6. 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. 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. 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. 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. 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. 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. 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. 13. A Closer Look on Adventist Health Study 2 and EPIC-Oxford … and cancer incidence in vegans. 13
  14. 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. 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. 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. 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. 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) 18
  19. 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. 19 ”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. 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. 20

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