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.