Thursday, October 15, 2009

Milk prevents colon cancer?

We physicians get a great many free publications.

One that comes regularly is a trade journal called The Medical Post, and in it the Dairy Farmers of Canada are regular advertisers making half page buys geared to look like articles that they entitle Nutrition and the Physician. These pieces in turn are generally written or at the very least attributed to physicians, professors and dietitians highlighting some benefit of dairy consumption.

For a long while the bulk of these medical advertisements were about milk's role in weight management but that died off shortly after Big Milk in the US agreed with the Federal Trade Commission that claims regarding milk and weight loss/management were preliminary at best.

The most recent version I read was about milk products and the prevention of colon cancer and it is attributed to Dr. Parviz Ghadirian, the Director of the Epidemiological Research Unit at the Hotel-Dieu hospital in Montreal and a Professor in the Department of Nutrition at the University of Montreal.

The advertisement rightly points out that there is indeed some evidence to suggest a modest risk reduction for colorectal cancer with the consumption of diets high in dairy.

So what's my problem?

I've got a few.

Let's start with the opening paragraph where Dr. Ghadirian quotes from the World Cancer Research Fund report, "milk probably protects against colorectal cancer". The quote is true, I looked it up. Problem here is that it's not the full quote. The full quote reads,

"The strongest evidence, corresponding to judgements of ‘convincing’ and ‘probable’, shows that milk probably protects against colorectal cancer, and that diets high in calcium are a probable cause of prostate cancer"
Funny the advertisement doesn't mention anything about prostate cancer risk and hmm, isn't milk high in calcium?

Oh, and about calcium, next I looked at the meta-analysis Dr. Ghadirian referred to which demonstrated a 22% risk reduction in adults who consumed higher quantities of milk. In it I learned that calcium supplementation alone confers a virtually identical risk reduction (and in fact slightly greater) to that seen with milk products as noted by the authors in the paper's discussion,
"Interestingly, both dietary and supplemental sources of calcium showed inverse effects, with the latter reducing colorectal cancer risk by 24%"
Strange how Dr. Ghadirian's advertisement doesn't mention that fact.

Next I pulled the large prospective cohort study he referred to which demonstrated a 28% colon cancer risk reduction in women who consumed higher quantities of milk products and 15% in men. In it I learned that the results showed that in men dairy intake did associate with lower colorectal cancer incidence but again was positively associated with prostate cancer. Interestingly while the relationship between calcium supplementation and decreased colorectal cancer risk held in men, in this study non-dairy calcium supplementation did not increase prostate cancer risk,
"dairy food intake was inversely associated with cancers of the head and neck, esophagus, stomach, colorectum, and bladder, whereas it was positively associated with prostate cancer"

"Total calcium intake was significantly related to a lower risk of colorectal cancer and showed a weak inverse association with kidney cancer. On the other hand, total calcium intake was not related to prostate cancer."
Next I pulled the pooled analysis he refers to and once again the pooled study's findings were applicable both to plain old calcium supplementation as well as milk but interestingly they pointed out something else,
"Cheese intake was weakly positively associated and yogurt intake was weakly inversely associated with colorectal cancer risk".
What's that, cheese might increase colon cancer risk?

Let's take a look at the World Cancer Research Fund's report on cheese - did they find it might increase colon cancer risk? Yup.
"There is limited evidence suggesting that cheese is a cause of colorectal cancer."
Hey, isn't cheese a milk product?

So what did Dr. Ghadirian's medical advertisement say on cheese,
"A study using the Swedish Mammography Cohort of 60,708 women that included approximately 15 years of follow-up suggests that consumption of higher fat milk products (especially cheese) and the CLA in dairy fat are also important in reducing risk."
Pulling the Swedish study one learns that the researchers weren't clear on why their results on cheese differed from everyone else's and they hypothesized that it might have to do with the fact that their cohort ate a tremendous amount of cheese and admit that the differences in their diets don't stop there leading me to wonder if perhaps they're not the greatest population upon which to draw global, or at least North American, conclusions.

So to summarize Dr. Ghadirian's milk sponsored medical advertisement: Milk products, especially cheese, reduce the risk of colon cancer.

To summarize the actual medical literature used by Dr. Ghadirian: Milk products decrease the risk of colon cancer to a degree pretty much identical to that seen with calcium supplementation but at the same time in men increases their relative risk of prostate cancer, while diets high in cheese potentially increase colon cancer risk except in Sweden.

My advice to my dear readers? If you read anything sponsored by the Dairy Farmers of Canada you'll probably want to read the studies themselves before drawing any conclusions, and if Big Milk comes a' knockin' on your door asking you to write one of their medical advertisements tell them, "no thank you" and while you might lose a few bucks of chump change (literally perhaps), at least you'll keep your ethics.

And here I'm really at a loss. Dr. Ghadirian is a world class researcher and epidemiologist. How is it that he agreed to put his name on an advertisment that omits such highly pertinent data?

Huncharek, M., Muscat, J., & Kupelnick, B. (2009). Colorectal Cancer Risk and Dietary Intake of Calcium, Vitamin D, and Dairy Products: A Meta-Analysis of 26,335 Cases From 60 Observational Studies Nutrition and Cancer, 61 (1), 47-69 DOI: 10.1080/01635580802395733

Park, Y., Leitzmann, M., Subar, A., Hollenbeck, A., & Schatzkin, A. (2009). Dairy Food, Calcium, and Risk of Cancer in the NIH-AARP Diet and Health Study Archives of Internal Medicine, 169 (4), 391-401 DOI: 10.1001/archinternmed.2008.578

Cho E, Smith-Warner SA, Spiegelman D, Beeson WL, van den Brandt PA, Colditz GA, Folsom AR, Fraser GE, Freudenheim JL, Giovannucci E, Goldbohm RA, Graham S, Miller AB, Pietinen P, Potter JD, Rohan TE, Terry P, Toniolo P, Virtanen MJ, Willett WC, Wolk A, Wu K, Yaun SS, Zeleniuch-Jacquotte A, & Hunter DJ (2004). Dairy foods, calcium, and colorectal cancer: a pooled analysis of 10 cohort studies. Journal of the National Cancer Institute, 96 (13), 1015-22 PMID: 15240785

Larsson SC, Bergkvist L, & Wolk A (2005). High-fat dairy food and conjugated linoleic acid intakes in relation to colorectal cancer incidence in the Swedish Mammography Cohort. The American journal of clinical nutrition, 82 (4), 894-900 PMID: 16210722