Study: Vegans Have A 35% Lower Risk For Prostate Cancer, Vegans Who Eat Dairy Do Not

VeganPlateArticles about a study showing vegan diets were protective against prostate cancer are all over the news right now. Here are some:

New Research Shows Vegan Diets Could Lower Prostate Cancer Risk, World Cancer Research Fund UK, 3 March 2016
Vegan Diet ‘cuts Prostate Cancer Risk By 35%’, Daily Mail, 3 March 2016
Vegan Diet ‘Cuts Prostate Cancer Risk By 35%’, Huffington Post UK, 3 March 2016

I believe this is the study:
Are Strict Vegetarians Protected Against Prostate Cancer?, American Journal of Clinical Nutrition, January 2016

Objective: This study aimed to examine the association between dietary patterns (nonvegetarian, lacto-ovo-vegetarian, pesco-vegetarian, vegan, and semi-vegetarian) and prostate cancer incidence among 26,346 male participants of the Adventist Health Study-2.

Design: In this prospective cohort study, cancer cases were identified by matching to cancer registries.

Results: In total, 1079 incident prostate cancer cases were identified. Around 8% of the study population reported adherence to the vegan diet. Vegan diets showed a statistically significant protective association with prostate cancer risk (HR: 0.65; 95% CI: 0.49, 0.85). After stratifying by race, the statistically significant association with a vegan diet remained only for the whites (HR: 0.63; 95% CI: 0.46, 0.86), but the multivariate HR for black vegans showed a similar but nonsignificant point estimate (HR: 0.69; 95% CI: 0.41, 1.18).

Conclusion: Vegan diets may confer a lower risk of prostate cancer. This lower estimated risk is seen in both white and black vegan subjects, although in the latter, the CI is wider and includes the null.

Here’s a chart from the study. They looked at 4 “vegetarian” diets (vegan, lacto-vegetarian, pesco-vegetarian, semi-vegetarian) and compared them to a nonvegetarian diet. Click to enlarge.

VeganProstateCancerTable

In a multivariate model, where they adjusted for confounders, men who ate a vegan diet, which contains no animal food, had a 35% lower risk of prostate cancer (HR: 0.65).

But, look at this … when vegans ate dairy food (lacto-vegetarian) they lost that protective effect! A lacto-vegetarian diet was similar to a nonvegetarian diet when it came to prostate cancer. You can also see from the table that pesco-vegetarians (fish-eaters) and semi-vegetarians were also no better than nonvegetarians.

Why would just adding, say, cheese to a vegan diet cause a loss of protection against prostate cancer? Perhaps it has something to do with: “Harvard: Dairy Food Is One Of The Most Consistent Predictors For Prostate Cancer In The Published Literature“.

As you know, smoking is a powerful risk factor for cancer. An advantage of studying Adventists:

There is also diminished confounding by smoking and alcohol consumption, because these substances are avoided by most Adventists.

Also of note:

BMI does not seem to substantially modify these associations, despite being strongly associated with dietary pattern.

Not even controlling their weight seemed to help.

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