There’s a new report from Adventist Health Study-2 (AHS-2) comparing breast cancer incidence in vegetarians and vegans to non-vegetarians (1).

The study included 24,211 non-vegetarians, 3,748 vegans, 14,336 lacto-ovo vegetarians, 5,179 pesco-vegetarians, and 2,930 semi-vegetarians. Meat intake among non-vegetarians was quite low at less than a serving per day (54 g/day). Participants were followed for an average of 7.8 years (which isn’t very long for a cancer study).

All vegetarians combined had similar rates of breast cancer to non-vegetarians (0.97, 0.84-1.11), while vegans had a 22% lower risk that didn’t reach statistical significance (0.78, 0.58-1.05). After adjusting for body mass index, the reduced risk was 15% for vegans (0·86, 0·62-1·21), indicating that lower body weight could explain some of the lower risk for vegans.

The authors write, “In conclusion, participants in this cohort who follow a vegetarian dietary pattern overall did not experience a lower risk of [breast cancer] as compared with non-vegetarians. However, those adhering to a vegan dietary pattern showed consistently lower point estimates in various subgroups but these were not statistically significant. Numbers of cancers in vegans were relatively small, and these analyses should be repeated in the AHS-2 cohort after a longer follow-up to determine whether the same trends continue when power is greater.”

I have posted these results in the VeganHealth.org article Cancer, Vegetarianism, and Diet.

References

1. Penniecook-Sawyers JA, Jaceldo-Siegl K, Fan J, Beeson L, Knutsen S, Herring P, Fraser GE. Vegetarian dietary patterns and the risk of breast cancer in a low-risk population. Br J Nutr. 2016 Mar 18:1-8. • link

Dr. Michael Greger has some very interesting videos on the history of using vitamin C for cancer treatment:

Intravenous Vitamin C for Terminal Cancer Patients

Vitamin C Supplements for Terminal Cancer Patients

He also recently ran two very interesting videos discussing the role of fiber in weight loss:

Are There Foods With Negative Calories?

Eating More to Weigh Less

The Adventist Health Study-2 has published results of their study on prostate cancer risk among various diet groups after 7.8 years of follow-up.

Vegans were shown to have a 34% lower risk of being diagnosed with prostate cancer than regular meat-eaters. The other diet groups were not found to be statistically different than regular meat-eaters. Here are the confidence intervals:

• Non-Veg: 1.00
• Semi-Veg: 1.18 (.91, 1.54)
• Pesco: 1.07 (.88, 1.31)
• Lacto-Ovo: .96 (.83, 1.12)
• Vegan: .66 (.50, .87)

The results were adjusted for age, race, family history, education, screening, caloric intake, and body mass index. There were 2,140 vegans in the study.

A similar trend was found when looking only at African American participants, but the results didn’t reach statistical significance.

Among those diagnosed with advanced prostate cancer (as distinct from all types of prostate cancer) vegans had a 30% reduced risk, but it wasn’t statistically significant.

The authors speculated on a number of mechanisms that could be responsible for the lower rates among vegans:

• Lower levels of insulin-like growth factor 1
• Lower insulin resistance
• Lower calcium intakes increasing the need for the conversion of vitamin D into its active form which might reduce prostate cancer
• Reduced inflammation due to higher antioxidant intakes
• Increased soy consumption which has been linked to lower prostate cancer risk (with a large number of possible mechanisms)

I have updated the prostate cancer section of the VeganHealth.org article, Cancer, Vegetarianism, and Diet.

I have updated the VeganHealth.org article Cancer, Vegetarianism, and Diet with results from the Netherlands Cohort Study-Meat Investigation Cohort (1).

The study found that vegetarians had a non-statistically significant, reduced risk for colorectal cancer. In comparison to non-vegetarians, the rate for vegetarians was .78 (.51, 1.20) when adjusted for age and gender, and .89 (.58, 1.39) when further adjusted for energy, smoking, alcohol, body mass index, physical activity, and education.

It follows a long line of research that has mostly found non-significant differences between vegetarians and non-vegetarians for colorectal cancer (see Table 3).

Some other interesting findings from the report:

– Fiber and soy product intake contributed most to the observed inverse risk.

– People who ate meat only once a week had a borderline statistically lower risk (.72, .52-1.00) than those eating meat 6-7 days per week in the model adjusting only for age and gender. Adjusting for the remaining variables (mentioned above) weakened the association.

– Substituting 5% of energy from meat protein with 5% of energy from dairy protein was associated with a 24% reduced risk of colorectal cancer, after adjustment for confounding variables (P=0.055). Dairy products may protect against colorectal cancer risk due to their high calcium content.

This is only a very small piece of the puzzle on diet, meat, dairy, vegetarianism and colorectal cancer, but it underlines the recommendations that vegans make sure they’re getting enough calcium.

In summary, there is some good news here, but it suggests that vegans get enough calcium.

1. Gilsing AM, Schouten LJ, Goldbohm RA, Dagnelie PC, van den Brandt PA, Weijenberg MP. Vegetarianism, low meat consumption and the risk of colorectal cancer in a population based cohort study. Sci Rep. 2015 Aug 28;5:13484. | link | PDF Available

EPIC-Oxford and Adventist Health Study-2 (AHS-2) are the two ongoing studies of diet and disease that contain a large number of vegans. This past week, AHS-2 released a report on colorectal cancer rates among various diet groups (1).

In summarizing the research on diet and colorectal cancer to date, the researchers write:

“Among dietary factors thought to influence risk, the evidence that red meat, especially processed meat, consumption is linked to increased risk and that foods containing dietary fiber are linked to decreased risk has been judged to be convincing. The evidence for a link to decreased risk has been judged as probable for garlic, milk, and calcium. Evidence for other dietary components is considered limited.”

Because of the link with red and processed meat, nutritionists had expected that vegans and vegetarians would have a lower risk for colorectal cancer. To date, EPIC-Oxford has not shown a lower risk for vegetarians (results can be seen in Cancer, Vegetarianism, and Diet).

Better news comes from the latest AHS-2 report. After an average follow-up of 7.3 years, the lacto-ovo vegetarians and vegans had a lower risk of colorectal cancer (18% and 16% respectively), but the findings were not statistically significant. Here are the risk ratios and confidence intervals for each group:

The only group with a statistically significant lower risk was the pesco-vegetarians (who eat no meat other than fish), with a 43% lower risk that was highly statistically significant. Despite this, the difference between the pesco-vegetarians and vegans was not statistically significant, though close (.68, .43-1.08).

When lumping all the groups together (semi-, pesco-, lacto-ovo, and vegan) and comparing to non-vegetarians, the “vegetarians” had a statistically significant, 22% lower risk of colorectal cancer (.78, .64-.95).

Results were adjusted for age, race, gender, education, exercise, smoking, alcohol, family history, peptic ulcers, inflammatory bowel disease, diabetes mellitus, aspirin, statins, prior colonoscopy or flexible sigmoidoscopy, supplemental calcium, supplemental vitamin D, calories, and hormone therapy. Subjects were excluded if they had a prior diagnosis of cancer (except for non-melanoma skin cancer).

Overall, colorectal cancer rates in AHS-2 were lower than the population at large and AHS-2 non-vegetarian eat very little meat (54.5 g/d or just 4.5 servings per week).

Could a higher calcium intake for vegans lower their risk of colorectal cancer? In AHS-2, the vegans had slightly lower calcium intakes (801 mg/day) than the pesco-vegetarians (913 mg/day) and non-vegetarians (882 mg/day). But in EPIC-Oxford, where the results were not as positive for vegetarians, vegans had much lower calcium intakes (583 mg/day compared to 1,005 mg/day for non-vegetarians) (2).

Another difference between the EPIC-Oxford and AHS-2 groups is that the AHS-2 vegans had a substantially greater intake of both dietary fiber and vitamin C.

Does eating fish protect against colorectal cancer? The researchers write, “The existing literature provides some, although inconsistent, support for a possible protective association for fish consumption, particularly for rectal cancer; evidence for omega-3 fatty acid consumption is limited and inconsistent.” In other words, it’s not clear.

In summary, colorectal cancer rates in vegans in AHS-2 are promising, but it might be important for vegans to follow calcium recommendations not only for bone health but also to prevent colorectal cancer.

References

1. Orlich MJ, Singh PN, Sabaté J, Fan J, Sveen L, Bennett H, Knutsen SF, Beeson WL, Jaceldo-Siegl K, Butler TL, Herring RP, Fraser GE. Vegetarian Dietary Patterns and the Risk of Colorectal Cancers. JAMA Intern Med. 2015 Mar 9. [Epub ahead of print] | link

2. Average calcium intakes for EPIC-Oxford calculated from Nutrient Intakes of Vegetarians and Vegans.

The Oxford arm of the European Prospective Investigations Into Cancer (EPIC) has released a report showing that after an average of 14.9 years of follow-up, vegetarians (.88, .82-.95) and pesco-vegetarians (.88, .80-.97) each have a 12% lower risk of cancer than other meat-eaters (1).

Breaking the participants into smaller diet groups showed that vegans had a 19% lower risk of cancer:

Pesco – .88 (.80, .97)
Lacto-ovo – .89 (.83, .96)
Vegan – .81 (.66, .98)

I have updated the General Cancer section of the VeganHealth.org article, Cancer, Vegetarianism, and Diet. If you go there, you can see that the findings for vegans were similar to those in the Adventist Health Study-2 (AHS-2), the other ongoing study containing a large number of vegans.

Unlike the findings for vegans and diabetes, the statistical significance of these findings for cancer are not large. I like confidence intervals to be tighter before I get too excited about saying a vegan diet can prevent a disease. However, the consistency between EPIC-Oxford and AHS-2 should provide some assurance.

Some notes on these findings:

– The results above are not adjusted for body mass index (BMI). Adjusting for BMI slightly changed the findings for vegetarians (.90, .93-.96) and for vegans (.82, .68-1.00).

– The previous report from EPIC-Oxford had followed participants through 2005 while this current report followed them through 2010. In the intervening years, cancers increased 50%.

– Diets were assessed at baseline and after 5 years; 88% of the participants remained in their original diet category.

– No single specific cancer type could explain the differences between the diet groups; to date there has been very little consistency found between the various cancers (such as colorectal) and diet group.

Reference

1. Key TJ, Appleby PN, Crowe FL, Bradbury KE, Schmidt JA, Travis RC. Cancer in British vegetarians: updated analyses of 4998 incident cancers in a cohort of 32,491 meat eaters, 8612 fish eaters, 18,298 vegetarians, and 2246 vegans. Am J Clin Nutr. 2014 Jun 4. | link

If you’ve read my articles on soy (Response to Not Soy Fast, Soy: What’s the Harm), there’s nothing new here, but it’s good to hear it from an organization like the American Cancer Society (ACS):

The Bottom Line on Soy and Breast Cancer Risk
August 02, 2012
By Marji McCullough, ScD, RD

Excerpt:

“Bottom line: Even though animal studies have shown mixed effects on breast cancer with soy supplements, studies in humans have not shown harm from eating soy foods. Moderate consumption of soy foods appears safe for both breast cancer survivors and the general population, and may even lower breast cancer risk. Avoid soy supplements until more research is done. So, enjoy your occasional tofu stir-fry or tofu burger – they are unlikely to increase your risk of breast cancer and, on balance, are some of the healthier foods you can eat!”

Warning: There are the typical Weston Price Foundation-type comments after the article – the myths about Asians eating only fermented soy and fermented soy being significantly different than other soy. Too bad they allow comments which will possibly just serve to scare people. And I realize that I’m saying that as someone who allows comments on my own blog, but it’s one thing to be an RD blogger and another to be the strategic director of nutritional epidemiology for the ACS. Of course, that doesn’t mean Dr. McCullough is infallible, but if someone whose opinion is worthwhile has an objection to her article, they can contact the ACS behind the scenes and she can correct the article if they have a valid point. Just my two cents!

(Thanks, Matt.)

On November 26, 2012, I wrote about a report from Adventist Health Study-2 looking at the cancer rates of vegans, Direct Evidence that Vegans have Lower Cancer Rates.

Two days later, after a reader brought it to my attention, I posted a Follow-Up, pointing out that the authors had not included physical activity as a variable in their multivariable adjustment model. For a number of reasons, I suspected that if they had adjusted for physical activity, the finding that vegans have lower cancer rates would no longer be statistically significant.

I have since corresponded with one of the authors of the paper, Yessenia Tantamango, who told me that when they included physical activity in the multivariable analysis (in the model that did not include BMI), vegans had a cancer rate of .85 (.73-.99) which is statistically significant.

The original finding for the vegan cancer rate was .84 (.72-.99). An upper confidence interval limit of .99 is only of borderline significance; if it were 1.00 it would not be considered significant. In other words, I realize we are splitting hairs here. But I wanted to follow-up to let readers know that after adjusting for physical activity the finding was still statistically significant and so, by conventional nutrition science standards, it is legitimate to say that vegans had a lower rate of cancer in this study and there is reason to think it was due to their diet.

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. 2012 Nov 20. | link

I’m a bit late in adding this info to the Prostate Cancer section of Omega-3 Fatty Acid Recommendations for Vegetarians.

There has been a question as to whether the short-chain omega-3 fatty acid, alpha-linolenic acid (ALA), might cause prostate cancer as a few early studies suggested. But from 2004 to 2010 there were three meta-analyses not finding this to be the case. The 2010 meta-analysis I just added to the site found that subjects who consumed more than 1.5 g/day of ALA had a significantly decreased risk of prostate cancer (0.95, 0.91-0.99) compared to those who ate less.

Reference

Carayol M, Grosclaude P, Delpierre C. Prospective studies of dietary alpha-linolenic acid intake and prostate cancer risk: a meta-analysis. Cancer Causes Control. 2010 Mar;21(3):347-55. Review. (Abstract)   |   Link

Wow – the post on Direct Evidence that Vegans have Lower Cancer Rates was one of my most popular ever. That could have partly been due to my asking people to share it with others – thank you to everyone who did that! And now, please unshare it. 🙁

I wrote the post on Monday evening. This morning (Wednesday) a reader, Dave, commented that after adjusting for BMI, the finding for vegans was no longer statistically significant AND that the authors had not adjusted for physical activity. I had not paid proper attention to either of these facts, partially due to not reading the charts in the study correctly.

The authors found significantly more physical activity among those who did not get cancer and also among the vegans, so it is quite odd that they did not adjust for physical activity. But since they did not, and while this study still shows vegans to have lower cancer rates, I no longer consider the study to be evidence that a vegan diet leads to lower cancer rates, which is the whole idea. I have corrected the original post to reflect this.

I sincerely apologize to everyone for doing such a poor job analyzing the study and then asking people to share it.

This post has a follow-up:

Take Three: Direct Evidence that Vegans have Lower Cancer Rates

– Jack