Archive for the ‘Cancer’ Category

Incidence of Colorectal Cancer in Vegans

Saturday, March 14th, 2015
Summary Results from Adventist Health Study-2 show vegans to have a 16% lower risk of colorectal cancer than non-vegetarians, but the finding wasn’t statistically significant. Pesco-vegetarians had the lowest rate of all.

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:

Non-Veg 1.00
Semi-Veg  .92 (.62, 1.37)
Pesco  .57 (.40, .82)
Lacto-ovo  .82 (.65, 1.02)
Vegan  .84 (.59-1.19)

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.

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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.

Lower Cancer Rates in Vegans

Monday, June 16th, 2014
Summary A report out this month shows vegans and vegetarians in EPIC-Oxford to have lower cancer rates than regular meat-eaters.

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

American Cancer Society on Soy & Breast Cancer

Tuesday, April 30th, 2013

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.)

Take Three: Direct Evidence that Vegans have Lower Cancer Rates

Wednesday, January 2nd, 2013

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

VeganHealth.org Update: ALA Not Associated with Prostate Cancer

Friday, December 7th, 2012

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

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

Wednesday, November 28th, 2012

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

Direct Evidence that Vegans have Lower Cancer Rates

Monday, November 26th, 2012

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

2012 meta-analysis on veg mortality and cancer incidence

Tuesday, June 12th, 2012

A new meta-analysis on vegetarian mortality and cancer has been released (1). It found a statistically reduced rate for vegetarians in terms of ischemic heart disease mortality and cancer incidence. It did not find a difference for all cause mortality or stroke.

Comments I have added to Disease Rates of Vegetarians and Vegans on VeganHealth.org:

“Although the 2012 meta-analysis by Huang et al. (1) is more recent, it may not be as reliable as the 1999 meta-analysis [by Key et al.] because it includes a 1984 study on Zen priests (2) who were mostly semi-vegetarian and which used a standardized mortality ratio (comparing all the Zen priests to the greater population rather than comparing the “vegetarians” to non-vegetarians within the same group). The Heidelberg Study results were also included and its control group was semi-vegetarians, which means there were semi-vegetarians in both the “vegetarian” and “non-vegetarian” group in the 2012 meta-analysis; while this is not ideal, it should have biased the results against finding a beneficial effect of a vegetarian diet. In its favor, the 2012 meta-analysis includes data from EPIC-Oxford that was not available for the 1999 meta-analysis.”

There is a table with the confidence intervals at the link above.

Reference

1. Huang T, Yang B, Zheng J, Li G, Wahlqvist ML, Li D. Cardiovascular Disease Mortality and Cancer Incidence in Vegetarians: A Meta-Analysis and Systematic Review. Ann Nutr Metab. 2012 Jun 1;60(4):233-240. (Link)

2. Ogata M, Ikeda M, Kuratsune M. Mortality among Japanese Zen priests. J Epidemiol Community Health. 1984 Jun;38(2):161-6. (Link)

Vegetarian Diet associated with Younger Age of Menopause

Wednesday, May 30th, 2012

A cross-sectional study from the United Kingdom (the Breakthrough Generations Study) found that self-described vegetarians were more likely to have an earlier age of natural menopause. In turn, a lower age of menopause has been associated with lower rates of breast cancer.

The authors wrote:

“Vegetarians reached menopause at a mean age of 50.1 years, which was significantly earlier than non-vegetarians (mean menopausal age = 50.7 years, HR = 1.12; P < 0.001). The effect was present regardless of whether the woman became vegetarian before 20 years of age or between the ages of 20 and 40 years (data not shown)." This confirms previous reports that vegetarians have a lower age of menopause. Reference

Morris DH, Jones ME, Schoemaker MJ, McFadden E, Ashworth A, Swerdlow AJ. Body mass index, exercise, and other lifestyle factors in relation to age at natural menopause: analyses from the breakthrough generations study. Am J Epidemiol. 2012 May 15;175(10):998-1005. | link

Ginny: When Vegans Get Cancer

Tuesday, May 29th, 2012

Ginny Messina: When Vegans Get Cancer