Direct Evidence that Vegans have Lower Cancer Rates

For decades, vegans have been saying that vegans have lower rates of cancer. Until now, there was no direct evidence for this. But last week a report from Adventist Health Study-2 was released showing vegans to have a lower cancer rate than regular meat-eaters. Unfortunately, there is not enough evidence to conclude that it is due to the diet.

There were 4,922 vegans in the study. After 4.1 years of follow-up and breaking the population into five categories (regular meat-eaters, semi-vegetarians, pesco-vegetarians, lacto-ovo vegetarians, and vegans) vegans had a 16% reduced risk of cancer when compared to regular meat-eaters (.84, .72-.99). Vegans were the only diet category to have a statistically significant lower risk of cancer.

These results were adjusted for age, race, family history of cancer, education, smoking, alcohol, age at menarche, pregnancies, breastfeeding, oral contraceptives, hormone replacement therapy, and menopause status. When the results were also adjusted for body mass index (BMI), the findings for vegans were no longer statistically significant (.86, .73 – 1.00). Additionally, the results were not adjusted for physical activity even though the authors found significantly more physical activity among those who did not get cancer and also among the vegans. Since physical activity could have affected the vegans’ BMI, you cannot rule out that it was simply more physical activity among the vegans that led to lower cancer rates and not the vegan diet.

When combining all the vegetarian categories and comparing them as a whole to the regular meat-eaters, the “vegetarians” had an 8% lower risk of cancer (.92, .85 -.99), but the “vegetarians” included some people who eat meat (the semi- and pesco-vegetarians). Using the BMI-adjusted model changed the finding a tad (.92, .85 – 1.00).

The follow-up period was only an average of 4.1 years – that’s not very long for a study on cancer. Hopefully, Adventist Health Study-2 will do some longer follow-up on cancer rates.

You can see the cancer rates of the other diet groups in Table 2 of the article Cancer, Vegetarianism, and Diet at VeganHealth.org.

This post has two follow-ups:

Follow-Up to: Direct Evidence that Vegans have Lower Cancer Rates

Take Three: Direct Evidence that Vegans have Lower Cancer Rates

Reference

Tantamango-Bartley Y, Jaceldo-Siegl K, Fan J, Fraser G. Vegetarian diets and the incidence of cancer in a low-risk population. Cancer Epidemiol Biomarkers
Prev. 2013 Feb;22(2):286-94. | link

27 Responses to “Direct Evidence that Vegans have Lower Cancer Rates”

  1. Bertrand Russell Says:

    Jack, did this study correct for other lifestyle factors? Excercise, smoking, obesity, etc.?

  2. Jack Norris RD Says:

    Bertrand,

    It adjusted for: age, gender, race, family history of cancer, education, smoking, alcohol, age at menarche, pregnancies, breastfeeding, oral contraceptives, hormone replacement therapy, menopause status.

  3. Phil Says:

    Interesting study, but does this mean that the vegetarians (including semi- and pesco-vegetarians) were only 1% less likely to get cancer than the vegans?

  4. Jack Norris RD Says:

    Phil,

    I’m not sure where you get the 1% figure. Here are the confidence intervals for the diet groups:

    Non-Veg 1.00
    Semi .98 (.82, 1.17)
    Pesco .88 (.77, 1.01)
    Lacto-ovo .93 (.85, 1.02)
    Vegan .84 (.72, .99)

    The group coming closest to the vegans was the pesco-vegetarian at a 12% reduced risk.

  5. Phil Says:

    I got it from the following: “When combining all the vegetarian categories to the regular meat-eaters, the “vegetarians” had a 16% lower risk of cancer…” The difference between this group and the vegan group (at 17% reduced risk) is 1%. Am I missing something?

  6. Jack Norris RD Says:

    Phil,

    The vegans were included in “all the vegetarian categories”. Does that make it clear?

  7. Rosario Says:

    wow! huge and nice news

  8. Rosario S. Says:

    Jack, can I translate your article in italian and post it on social networks?

  9. Jack Norris RD Says:

    Rosario,

    Sure, that would be great. Thanks!

  10. Idan Says:

    Is it true that the difference between pescetarians to the vegans was very small ? (Someone in a group said the difference was 3% after adjusting for BMI )

  11. Jack Norris RD Says:

    Idan,

    That’s true. It was .89 for pesco- and .86 for vegans after adjusting for BMI. I included the non-BMI adjusted version given that BMI and a vegan diet are closely correlated. I don’t mind it if the main reason that vegans would have a lower risk of cancer is due to their lower BMI. I would assume that is also primarily (though not entirely) the case for why vegans have a lower rate of type-2 diabetes.

  12. Jack Norris RD Says:

    Idan,

    Oops. After adjusting for BMI, vegans still have a tremendous advantage for type-2 diabetes, so I guess BMI doesn’t explain most of it: http://www.veganhealth.org/articles/diabetestwo

  13. Kathleen Keene Says:

    I am part of this study, (even though I am not Adventist anymore, but I still espouse the beliefs of veganism, not smoking/drinking, and Sabbath rest) and have been for years now.
    Yes, it did take into account smoking, alcohol and exercise. I get a questionnaire every couple years, and in the beginning, a HUGE questionnaire!

    You can look at all the newsletters with simple graphs and articles here:

    If you look on page 3 of this newsletter, you will see a graph showing early results (2006) of blood pressure, diabetes and arthritis correlation: http://www.llu.edu/assets/publichealth/adventist-health-studies/documents/2006-newsletter-african-american.pdf
    Here are the links I was telling you about:
    First, a general info link on the AHS-2: http://www.llu.edu/public-health/health/early_findings.page
    Early Descriptive Results: http://www.cpcsda.org/uploads/adventist-health-study-2.pdf
    Here is the general link to all the newsletters and findings: http://www.llu.edu/public-health/health/newsletters.page?

  14. Rosario S. Says:

    Which type of nutrition study is Adventist Health Study-2?

  15. Jack Norris RD Says:

    Rosario,

    It could be described as observational, cohort, and prospective.

  16. Idan Says:

    Kathleen Keene – do Adventists usually take b12 supplements ? do you take them?

  17. Dave Says:

    In the model that adjusted for BMI, the RR for vegans compared to meat eaters was 0.86 and this not statistically significant. Unlike Jack, I think that adjustment for BMI is needed in order to determine whether the reduced cancer rate is due to the diet.
    It should also be noted that the study did not adjust the results to exercise or sedentary time.

    PS: Jack, you have error in the RR for vegans: it is 0.84 (in the adjusted model without BMI) and not 0.83.

  18. Jack Norris RD Says:

    Dave,

    How dare you point out my total and complete ineptness? (Sigh.) It turns out I was looking at the footnotes for Table 4, not Table 3. So, not only did I use the wrong rate and CI, I thought that the BMI adjusted rate was still statistically significant and therefore, not really that big of a deal. Now that I have straightened it out (I hope), I have changed the post above and added a bit. I also added both adjustment models to the cancer article on VeganHealth.org.

    You make a good point that physical activity wasn’t included and that could account for BMI difference – another thing I shouldn’t have overlooked. They adjusted for physical activity in their diabetes follow-up, so I wonder why they didn’t bother here.

    So, the finding is not as impressive as I originally thought (and it wasn’t even all that impressive in my original thought, just enough to say that there was some evidence to claim vegans have a lower rate of cancer) so I wonder if I should make a follow-up post pointing out these errors.

  19. Amanda Says:

    I really don’t think there are health benefits of veganism independent of the nutrients we tend to eat more of and the toxins we tend to eat less of. By that, I mean that health conscious meat-eaters, who pay attention to their saturated fat intake as well as fiber and minerals, probably will fare the same as any vegan. However, as a group vegans have a disproportionate amount of health-conscious people who pay attention to nutrient intake.

    Not to be a downer, but it makes me feel disingenuous to present this to the scientifically illiterate as evidence of the health benefits of veganism, and I feel that it can backfire. And yes, I know that the fear-mongering AGAINST veganism is worse than any exaggeration we could ever make in our favor, but two wrongs don’t make a right.

  20. Kathleen Keene Says:

    Idan Says: Kathleen Keene – do Adventists usually take b12 supplements ? do you take them?

    Some do, I do sometimes. A lot of “hard core” Adventists need to take them, because just as “hard core” vegans don’t eat supplemented foods like soy milks or other processed foods like cereal, burgers, etc, and they mostly eat whole foods; those people would need to supplement. I am not in that hard core group, as I eat some veggie burgers, motherless milks, and other fortified foods.

    There probably is a definitive answer to that question, as we were asked that question at some point on one of the questionnaires.

    It should be put out there the percentages of people in the AHS-2 that are vegan, vegetarian, and so on.

    Based on the analysis of 27 relevant food questions,
    4.2% are total vegetarian,
    31.6% lacto-ovo-vegetarian,
    11.4% include fish (pescatarian),
    6.1% are semi-vegetarian (eat meat <1 time/week) and
    46.8% are non-vegetarian.
    A wide distribution is also seen in the consumption of other foods; for instance, 25% drink soymilk several times per week and 66% eat nuts two or more times per week.

    http://www.llu.edu/public-health/health/index.page?rsource=adventisthealthstudy.com

  21. Cheryl Hugle Says:

    I think The China Study explains a much more important and comprehensive study involving many more people and it also explains how cancer is promoted in the body. I think this article is very misleading especially in its claim that this study was a ‘first’.

  22. Jack Norris RD Says:

    Cheryl,

    What study are you talking about, the actual China Study that was conducted in China?

  23. Kathleen Keene Says:

    The China Study is important, yes. I love the book, and T. Colin Campbell. However, the Adventist Health Studies have been so enlightening in many ways. The first study showed that people who eat more fruits and vegetables have lower rates of cancer, and this was in the 70s. (AHS-1) This study is still referred to in major publications. Loma Linda University (the university that is undertaking this long term study) has made great advancements, and I look forward to them making more advancements with the incoming information.

    I just sent in a questionnaire about a month ago, and this study has been going on since 2002. There are also way more people in the AHS than in the China Study. (about 96,000 in AHS-2, compared to 6,500 in the China Study.)

  24. Cheryl Hugle Says:

    Yes, I am referring to the study done in China by T. Colin Campbell as well as the research he did in the Philippines before that.

    I think the findings are more significant for comparing plant based/vegan diets with diets inclusive of animal products.

    This study had 4% vegans and the participants were tracked for 4 years? and the vegans were included with other vegetarians to determine vegetarian vs non-vegetarian rates of cancer? It is hard to see how we get a clear picture of plant based/vegan vs animal based diets with that because so many ‘vegetarians’ rely heavily upon dairy and eggs.

    I am certainly in favor of more research and studies. I just don’t see what is significant about this particular study when much more compelling evidence favoring plant based diet exists.

  25. Jack Norris RD Says:

    Cheryl,

    > and the vegans were included with other vegetarians to determine vegetarian vs non-vegetarian rates of cancer?

    Only in one analysis. For the findings I primarily discuss in the blog post, the various diet groups were all separated from each other so they were comparing vegans to regular meat-eaters.

    And when the China Study compares disease rates between counties, the counties they compare all include meat-eaters, and very few adjustments were made. From what I can tell, the China Study can also be considered cross-sectional. So even though 4 years isn’t very long, it’s 4 years as compared to merely a slice in time in the China Study.

    This does not mean the China Study is wrong – it is what it is: a descriptive study finding lower animal product consumption in counties and also lower rates of chronic disease in those counties.

  26. Dave Says:

    The China study is an ecological study, which is one of the weakest forms of observetional studies. Therefore, its results are not interesting.

  27. Jack Norris RD Says:

    I have posted a follow-up to this discussion:

    Take Three: Direct Evidence that Vegans have Lower Cancer Rates

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