Cancer and Vegetarianism

On March 11, a study was released that measured the cancer incidence among British vegetarians. The study was part of European Prospective Investigation into Cancer and Nutrition–Oxford (EPIC-Oxford). I have updated the VeganHealth.org article Cancer, Vegetarianism, and Diet with the new findings.

(For this article to make sense you should take a minute to read this quick explanation of disease rate statistics if you are not already familiar with them.)

The participants in EPIC-Oxford were recruited from 1993 to 1999 and were followed through 2005. Previously, they had their overall cancer mortality through 2002 reported: Vegetarians had an 11% higher rate of death from cancer, but it was not statistically significant (1.11, .82 – 1.51).

The new findings reported the rates in two different ways:

1. Comparing vegetarians (including vegans) to all the meat-eaters.

2. Breaking the meat-eaters into two groups: regular and fish-eaters (no meat except fish).

The only statistically significant findings were:

  • Vegetarians had higher rates of colorectal cancer than all meat-eaters (1.49, 1.09-2.03).
  • Vegetarians had higher rates of colorectal cancer than the regular meat-eaters (1.39, 1.01-1.91).
  • Fish-eaters had lower rates of all cancer than regular meat-eaters (.83, .71-.96).
  • Vegetarians had borderline-significant, lower rates of all cancer than regular meat-eaters (.89, .80-1.00).

Rates for breast, prostate, lung, and ovarian cancer did not differ between groups.

When comparing this study population (including vegetarians and all meat eaters), their cancer rates were 28% lower than the overall population, their smoking rates were about half, and the meat-eating among the meat-eaters was “only moderate.” The authors hypothesized that, “Consumption of vegetables and fruit was higher among vegetarians than among nonvegetarians, but the differences were not large (< 20%). Thus, if high intakes of meat had an adverse effect and high intakes of fruit and vegetables had a beneficial effect, the relatively low meat intake and high fruit and vegetable intake of the nonvegetarians in this cohort could reduce the chance of observing lower cancer rates in the vegetarians than in the nonvegetarians."

Although we consider cancer rates of 1.49 (1.09-2.03) and .83 (.71-.96) as being statistically significant, I'm starting to wonder how relevant measurements of this magnitude actually are. The studies on vegetarians that have shown statistical significance are pretty inconsistent, and most studies have not found statistical significance. On the other hand, if you look at how the smoking rates affected lung cancer in this study, heavy smokers had 87 times the amount of lung cancer (87.3, 37.8 – 202). Now that is statistical significance. Even light smokers (27.1, 11.1-66.4) and former smokers (6.54, 2.89-14.8) had many times the rates of lung cancer as nonsmokers.

If we include these latest findings of vegetarian cancer rates with the others that have been measured (listed in Cancer, Vegetarianism, and Diet), I think we start to get a fairly consistent picture:

Among vegetarians and people who eat moderate amounts of meat and don’t smoke, cancer rates are about the same, but lower than for people who do smoke and eat large amounts of meat. In other words, you can reduce your risk of cancer by not smoking, by limiting meat to moderate amounts (or abstaining entirely), and by eating plenty of fruits and vegetables. The evidence for stronger claims doesn’t seem to be there.

Similarly, the combined colon cancer rates to date seems to indicate that, in comparison to eating moderate amounts of meat, being vegetarian neither increases nor decreases your risk of colon cancer.

15 Responses to “Cancer and Vegetarianism”

  1. Jack Norris on Latest Epic-Oxford Results | Vegan.com Says:

    […] piece makes clear, vegans who think their diets erase their cancer risks are kidding themselves. Link. Spread the […]

  2. Fredrik Fälth Says:

    Thanks for posting!

    What about the vegans? Did the study compare the difference in health between vegans, and the rest?

  3. Rick Says:

    I am surprised to see that vegetarians have higher rates of colorectal cancer than non-vegetarians. There was a study published in one of the scientific journals earlier this decade showing, as I recall, higher rates of cancer of the the distal end of the colon in people who ate processed meat and the higher the consumption correlated to the higher the incidence of this cancer.

    Unless the EPIC-Oxford excluded or adjusted for people who eat processed meat from the non-vegetarian group, these data seem to conflict with the previous study.

    I will look for this study I referred to.

  4. Tracy Says:

    I wish the study had differentiated between vegans and vegetarians. I would like to see what the effect of consuming dairy products had on the cancer rates.

  5. Linus Says:

    I’m curious. Did they not separate out the vegans from vegetarians? How much does dairy items have as an impact on things?

  6. Barry Says:

    Hi Jack,

    Great post. It’s a good reminder that just having a different dietary choice doesn’t mean in itself that you’re disease proof.

    I’ve wondered why these sort of findings come about, and I think I have an idea for at least part of the reason. As a vegan, I’ve noticed that when eating outside the home, a ton of the time, the only options that might be available that qualify as “vegan” might be more less healthy (more fatty, more calories, less nutrients), compared to options that aren’t vegan. You might have only the french fries to choose, when other people can have the chicken and salad sandwiches, or have hash browns for breakfast when other people might have the muesli that has a small amount of dairy in it.

    This is not setting vegans up necessarily for better health, as you can imagine. I’ve been pretty pis*ed on a few ocassions that I simply can’t order anything healthy, while my friends are probably eating something that while it has animal products in it, is probably better for them than what I’m eating. This is why it’s vitally important for vegans to keep lobbying for healthy options, and phasing out junk food in our eating establishments worldwide. Nobody should have to tolerate poor diet options that might make them sick in the long run before their time.

  7. Jack Norris RD Says:

    Rick:

    > I am surprised to see that vegetarians have higher rates of colorectal cancer than non-vegetarians.

    Given that there are some studies that do not show higher rates, I think it would be too soon to say more than that vegetarians might have higher rates. My bet is that this is just a chance finding.

    > Unless the EPIC-Oxford excluded or adjusted for people who eat processed meat from the non-vegetarian group, these data seem to conflict with the previous study.

    Unlike lung cancer and smoking, a lot of studies on cancer and food conflict. They did not adjust for processed meat.

  8. Jack Norris RD Says:

    Tracy and Linus,

    There have been a lot of studies looking at dairy and various cancers — way too many for me to analyze. There have been no studies with enough vegans to measure our cancer rates with any accuracy. The studies comparing cancer rates of people eating various amounts of dairy have been mixed.

  9. Stig Harder Says:

    Jack Norris,

    As you will know by reading T. Colin Campbell’s “The China Study” (http://www.thechinastudy.com/), there is a direct causative link between dairy and breast cancer, prostate cancer and colorectal cancer. For this reason, it would be useful to compare vegans with vegetarians, vegans with meat eaters and vegetarians with meat eaters. By lumping vegans and vegetarians together, the researchers made the erroneous assumption that vegetarians’ consumption of dairy does not in a statistically significant way contribute to these forms of cancer.

    Stig Harder
    Director
    The Vegalitarian Society
    468 North Camden Drive
    Beverly Hills, CA 90210

  10. Kathie Says:

    What did these vegetarians/vegans in this diet eat? Many people calling themselves vegetarians eat plenty of dairy products and eggs, in addition to lots of highly processed foods such as protein isolates, highly processed packaged foods, white flours and lots of white sugar, high sodium foods, fried and baked goodies & junk foods such as vegan ice cream and candies and baked goods and soda pops and loads of sugared juices and junk drinks. How much water do they drink? Adding vegetable oils to the diet is not only not helpful, but detrimental to health. (I have an extremely difficult time finding good vegan food that has not been doused in oils.) Some, if not many, really enjoy their alcohol and other substances which may not be legal and go unreported. Point is: the majority of vegetarians that I have met do NOT eat a very healthy diet such as Dr. Joel Fuhrman or Dr. John McDougall or Brenda Davis, R.D. advocate! I would love to see this study analyzed by them.
    Also, a small amount of animal flesh or fluids added to a diet very high in whole foods of vegetables and greens and fruits and starches may very well not have any difference in cancer rates compared to a poor vegetarian or vegan diet! And then the poor vege diets may be detrimental.
    I sincerely wish that we as animal rights and vegan activists would get the message out about eating a truly healthy diet for a lifetime. Dr. Fuhrman calls it “nutritional excellence.” I agree with him. I also agree with him that the younger we start, the much better chances we have of avoiding diseases. Thus, what the children of this earth are eating is critical to their future health, the health of the planet, and the evolution of a more humane human animal in their attitudes towards all the other animals of this planet along with all human animals and the earth which we inhabit.
    Thanks for bringing this study to our attention.

  11. george jacobs Says:

    Another point worth considering is that most European vegetarians started life as meat eaters. Most probably became vegetarians as teens or adults. Their diet in the pre-veg years may well have impacted their health.

  12. Jack Norris RD Says:

    Stig,

    I fully agree that it would be useful to compare vegans with lacto-ovo vegetarians.

    > the researchers made the erroneous assumption that vegetarians’ consumption of dairy does not in a statistically significant way contribute to these forms of cancer.

    I’m pretty sure the researchers are aware of the theories regarding dairy and cancer. They didn’t separate out the vegans because there were not enough vegans to get any data of any statistical significance. This study is ongoing and in future years they might have more data on vegans from which to draw.

    > there is a direct causative link between dairy and breast cancer, prostate cancer and colorectal cancer

    Studies measuring the link between dairy intake and the incidence of these cancers have had mixed results. You can read an article from 2001 about dairy and breast cancer here, to get an idea of the research. Prostate cancer had the strongest link with dairy, but even in that case the results have been mixed as you can see from this abstract of a 2008 meta-analysis.

  13. Rita Says:

    -a timely reminder that the reasons to go vegan are ethical, not, therapeutic. So long as we can take adequate care of our health (an option not open to much of the world), let’s use our increased life span to do something useful for all species – like veganism, for instance!
    Rita

  14. Jack Norris RD Says:

    Kathie,

    The authors listed the amounts of foods the different diet groups ate in broad categories (meat, fish, milk, cheese, vegetables, fresh fruit) but I have not seen a more extensive analysis of the diets. They also published a paper on the nutrient intakes of the people studied. The fat intake of the vegans was about 28% of calories, versus 30.5% for lacto-ovo vegetarians and 32% for the nonvegetarians. The vegans also ate 13% less calories, and the lacto-ovo vegetarians ate 4% less calories than the meat-eaters.

    Studies have shown that a very low-fat (5-10%) and/or primarily whole foods vegan diet provides benefits for many people with diabetes or heart disease. Since metabolic syndrome often precedes these diseases, it seems reasonable to say that it is also may be an excellent choice for people with metabolic syndrome.

    In my opinion, the case has not yet been made that a diet that low in fat is necessary to provide similar benefits for people with such conditions, or that a diet that low in fat is best for all vegans.

    The case has also not been made that a 90% or more whole foods diet (which could include more than 10% calories as fat through nuts, avocados, etc.) would significantly improve the health of all the vegans who currently eat a lower percentage of whole foods. I can see that there could be many cases in which someone needs a higher amount of protein than can be provided through a primarily whole foods vegan diet that meets caloric needs.

  15. Cancer and Vegetarianism - Grumpy Vegan Says:

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