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

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)

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 Messina: When Vegans Get Cancer

A study was released today showing that fiber intake was associated with a reduced risk of developing a colon polyp (.71, .59-.99). The clearest effect was of fiber from vegetables (including legumes) (0.65, .47-.90).

The study measured diet during the Adventist Health Study in 1976 and then followed up during the Adventist Health Study-2 between 2002 and 2005. The Adventist Health Study included a large proportion of vegetarians.

I only have access to the abstract at this time:

Tantamango YM, Knutsen SF, Beeson L, Fraser G, Sabate J. Association between dietary fiber and incident cases of colon polyps: the adventist health study. Gastrointest Cancer Res. 2011 Sep;4(5-6):161-7. (link)

I thought this was an interesting, short article worth passing on:

LiveScience.com: Did Alternative Medicine Kill Steve Jobs?

(Thanks, Matt.)

On April 27, Dr. Neal Barnard of PCRM wrote about a study, the Prostate Cancer Prevention Trial (1), which found that men with a higher percentage of DHA in their blood had a higher risk of high grade prostate cancer (Omega-3 Fatty Acids Linked to Prostate Cancer Risk). Dr. Barnard’s article also suggested that eating fish (the primary source of DHA for most people) five times or more a week could cause type 2 diabetes. People have written me asking if this means they should stop taking DHA supplements.

Based on the results from the Prostate Cancer Prevention Trial (PCPT) and some other studies, it is probably safe to conclude that large amounts of DHA do not prevent prostate cancer, but I think it is too soon to say that large amounts causes it. There are many variables when comparing percentages of fatty acids and disease, and the results tend to be all over the map. For example, the report from PCPT also found that the dreaded trans fats were inversely linked to high grade prostate cancer.

The levels of DHA in the blood of the men who had a higher rate of prostate cancer in the PCPT were >3.3% (compared to the lowest category of ≤2.6%), whereas vegans tend to have much lower levels of DHA, typically about 1% (see Omega-3 Fatty Acid Recommendations for Vegetarians).

DHA (and EPA) are normally promoted for reducing heart disease, but that is only a minor reason why I promote it for vegans. Vegans have much lower levels than omnivores and my concern is getting enough DHA for nerve tissue to function optimally. The amounts I recommend are much lower than what are typically suggested for fish oil supplements (usually 500 mg per day or more). I would not recommend taking that much DHA, EPA, or a combination.

It is still a good idea for vegans to take DHA at the rate of 200 to 300 mg every 2 to 3 days. The recent research does give me some pause in continuing to recommend 200 to 300 mg per day for those over 60 years old, cutting that down to every other day might be prudent. Unfortunately, there is no research showing how much these amounts of DHA will raise blood levels of DHA in vegans, but based on related research, I do not think it is enough to raise it much above 2%, which would still put someone in the lowest category of DHA percentage from the PCPT trial.

Reference

1. Brasky TM, Till C, White E, Neuhouser ML, Song X, Goodman P, Thompson IM, King IB, Albanes D, Kristal AR. Serum Phospholipid Fatty Acids and Prostate Cancer Risk: Results From the Prostate Cancer Prevention Trial. Am J Epidemiol. 2011 Apr 24. [Epub ahead of print] (Link)

A study from the USA was released Feb 25 showing that consuming up to 1/2 serving of soyfoods per day did not increase breast cancer recurrence among women previously diagnosed with breast cancer, and was even associated with lower mortality among such women.

The Women’s Healthy Eating and Living (WHEL) study is a randomized controlled trial of a high fruit/vegetable/fiber and low fat dietary intervention in early stage breast cancer survivors in the USA. It had a median follow-up of 7.3 years from the time of enrollment. Soy intake was measured post-diagnosis (median 2 years, range: 2 months to 4 years) using a food frequency questionnaire that included specific items for “Meat Substitutes (such as Tofu, Veggie Burgers),” and “Soy Milk”, as well as an opportunity to include other soy foods and supplements.

Isoflavone intake (the marker for soy) was unrelated to the risk of recurrence regardless of hormone receptor status or Tamoxifen use. No significant increased or decreased risk was associated with any specific level of intake. Risk of death tended to be lower as isoflavone intake increased (p for trend=0.02). Women at the highest levels of isoflavone intake (>16.3 mg/day isoflavones; equivalent to at least 1/2 cup soymilk or 2 oz tofu) had a non-significant 54% reduction in risk of death compared to the lowest quintile of soy intake.

The authors state:

Our study is the third epidemiological study to report no adverse effects of soy foods on breast cancer prognosis. These studies, taken together, which vary in ethnic composition (two from the US and one from China) and by level and type of soy consumption, provide the necessary epidemiological evidence that clinicians no longer need to advise against soy consumption for women diagnosed with breast cancer.

Reference

Caan BJ, Natarajan L, Parker BA, Gold EB, Thomson CA, Newman VA, Rock CL, Pu M, Al-Delaimy WK, Pierce JP. Soy Food Consumption and Breast Cancer Prognosis. Cancer Epidemiol Biomarkers Prev. 2011 Feb 25. Link

I finally got around to getting a copy of the EPIC study I posted on here. The study showed that adding 200 g of fruits and vegetables per day decreased the risk of cancer by 4%. What the reports didn’t mention was that people who ate more than 647 grams of fruit and vegetables per day (the equivalent of about 2 cups of broccoli plus 2 1/4 medium apples) had an 11% reduced risk of cancer compared to those who at only 226 g per day (the equivalent of about 3/4 apple plus 3/4 cup of broccoli).

Here are the confidence intervals:

On April 7, I linked to an NPR report about a European Prospective Investigation into Cancer (EPIC) paper that found that eating more fruits and vegetables cuts the risk of cancer by only 4%. After reading his comments elsewhere, I invited Paul Appleby, Senior Statistician at the Cancer Epidemiology Unit at the University of Oxford, to share his thoughts on the paper.

Paul writes…

Do fruits and vegetables prevent cancer? No. Does eating more fruits and vegetables reduce the risk of some cancers? Probably yes. To quote from the WCRF/AICR expert report on “Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective” (2007), “The strongest evidence, here corresponding to judgments of ‘probable’, shows that non-starchy vegetables and also fruits probably protect against cancers of the mouth, larynx, pharynx, oesophagus, and stomach, and that fruits also probably protect against lung cancer; and that allium vegetables, and garlic specifically, probably protect against stomach cancer.”

As I see it, there were two disappointing aspects to the EPIC paper in question (1). First, the authors examined the composite end point of all malignant cancers. Thus, the beneficial effects of fruit and vegetables at some cancer sites (see the WCRF/AICR list above) would be diluted by the inclusion of common cancer sites for which there appears to be no association with fruit and/or vegetable intake. As a result, the authors found only a small (but statistically significant) 3% reduction in overall cancer risk per 200 g/d increased intake of total fruits and vegetables. Although this would equate to the prevention of thousands of cancers every year, much of the media chose to put a rather negative spin on the story, overlooking the evidence for a beneficial effect of fruits and vegetables on other diseases such as cardiovascular disease (see, for example, ref 2 below). Interestingly, the latter study found that the “risk of coronary heart disease was decreased by 4% [RR (95% CI): 0.96 (0.93-0.99), P = 0.0027] for each additional portion per day of fruit and vegetable intake”, a benefit similar in magnitude to that found for cancer in the EPIC study. It is unrealistic to expect to see risk reductions of 10% or higher per extra portion of fruits and vegetables for such broad end points as all cancers or coronary heart disease.

The second disappointing aspect of the EPIC paper was the fact that the authors only considered total fruits and total vegetables (and the sum of the two) as their exposure variables, and did not look at sub-types of fruit and vegetables. As readers will be aware, different fruits and vegetables can have quite different nutritional characteristics (compare the vitamin C content of apples and oranges, for example) and it was a pity that the authors did not examine the associations between, say, citrus fruits or cruciferous vegetables and cancer risk. Such an analysis might have revealed stronger protective effects for certain types of fruit and vegetables that could have pointed the way to more nuanced public health advice to supplement the rather crude ‘5-a-day of any sort of fruits and vegetables’ message.

References

1. Boffetta P, et al. Fruit and vegetable intake and overall cancer risk in the European Prospective investigation Into Cancer and Nutrition (EPIC). J Natl Cancer Inst. 2010;102:1-9 Advanced access published April 6, 2010.

2. Dauchet L, Amouyel P, Hercberg S, Dallongeville J. Fruit and vegetable consumption and risk of coronary heart disease: a meta-analysis of cohort studies. J Nutr. 2006 Oct;136(10):2588-93.