Dairy Causes Cancer

In recent times, the rumor has been spreading that claims that dairy causes cancer. This myth is scary enough that it is causing some people to reconsider dairy. So let’s dig in and see if it is actually true. Does dairy actually cause cancer?

First of all, what is the basis of the claim that dairy causes cancer? It turns out that there are perhaps two major sources. For one, there is the claim popularized by Loren Cordain, author of The Paleo Diet, which is that a growth factor in milk called betacellulin may cause cancer.

Others argue that another growth factor – insulin growth factor 1 (IGF-1) – found in dairy causes cancer. For our purposes, we’ll consider these two arguments to be essentially the same – that some growth factor in dairy causes cancer.

Secondly, there are some interpretations of data, such as Colin Campbell’s The China Study, that purport that cancer rates are higher in populations with high rates of dairy consumption. Let’s look at each of these and see what the truth may be.

First, let’s look at the argument that claims that growth factors in milk cause cancer. Loren Cordain published a newsletter in which he cited 25 studies that he claims provide evidence that dairy causes cancers.

I am indebted to Chris Masterjohn for his article, Does Milk Cause Cancer? (Masterjohn, 2007), in which he does an excellent job analyzing the claim by looking at the actual studies cited by Cordain. So what do the studies show? Let’s take a look.

Both betacellulin and IGF-1 are present in whey and many whey products. The research shows that whey is actually protective against cancer. For example, in a paper titled, Whey proteins in cancer prevention (Bounous, Batist, & Gold, 1991), the authors state that “epidemiological and experimental studies suggest that dietary milk products may exert an inhibitory effect on the development of several types of tumors”. So already there is evidence strongly opposing the theory that dairy causes cancer.

Furthermore, studies have shown that conjugated linoleic acid (CLA), present in dairy fat, exerts a protective effect against some cancers. So even if growth factors such as betacellulin and IGF-1, when taken in isolation, may produce cancer growth, it seems that there are other highly protective factors in whole milk that not only prevent the growth factors from producing cancer, but may sometimes help prevent or reverse cancer from other causes.

When it comes to breast, colon, lung, stomach, and pancreatic cancers, the papers cited by Cordain fail to show any evidence of a connection between dairy consumption and cancer. In fact, many actually demonstrate the possibility that dairy consumption, particularly full-fat dairy, provides a protective effect in the case of many types of cancer.

However, there are two types of cancer that do have a positive correlation with low- or non-fat dairy consumption. Both ovarian and prostate cancers occur more frequently in populations who consume low-fat dairy. However, it turns out to be disingenuous to blame dairy, per se.

As the authors of one study write, “A high calcium intake, mainly from dairy products, may increase prostate cancer risk by lowering concentrations of 1,25-dihydroxyvitamin D3[1,25(OH)2D3], a hormone thought to protect against prostate cancer.” (Chan, et al., 2001) In other words, it’s not dairy, it’s low vitamin D. And guess what?

Full-fat dairy protects against both prostate and ovarian cancer. So the moral of the story is: don’t drink large amounts of skim milk and stay indoors all the time. Instead, eat some butter and get some sun. It’s good for the ovaries and prostate. The growth hormone in dairy theory of cancer is bunk.

In a word, no, he is not right. Denise Minger, author of Death by Food Pyramid has written some extensive critiques of Campbell’s conclusions in The China Study. And she specifically addresses some of Campbell’s claims regarding dairy causing cancer. Campbell has an ax to grind with regard to dairy, but it’s not clear that he’s got any legs to stand on, so to speak.

His argument is two-fold. First, he argues that in his laboratory he was able to “turn on and turn off cancer growth” in rats using casein, a protein from milk. Secondly, he argues that the numbers in The China Study demonstrate that dairy consumption positively correlates to cancer in populations. Let’s look at these arguments.

Next, let’s look at the claims made by Campbell and how they stand up to reality. Campbell is famously pro-vegan, and he is a darling among the plant-based diet contingent because he claims in The China Study that there is strong evidence that animal protein causes cancer, heart disease, diabetes, and all other forms of ill health.

He is particularly anti-casein, and he generalizes his anti-casein stance to dairy and then to all animal proteins. But is he right?

In a word, no, he is not right. Denise Minger, author of Death by Food Pyramid has written some extensive critiques of Campbell’s conclusions in The China Study. And she specifically addresses some of Campbell’s claims regarding dairy causing cancer. Campbell has an ax to grind with regard to dairy, but it’s not clear that he’s got any legs to stand on, so to speak.

His argument is two-fold. First, he argues that in his laboratory he was able to “turn on and turn off cancer growth” in rats using casein, a protein from milk. Secondly, he argues that the numbers in The China Study demonstrate that dairy consumption positively correlates to cancer in populations. Let’s look at these arguments.

The first argument is, perhaps, the more convincing of the two. Granted, lab rats are not humans, but nonetheless, being able to “turn on and turn off cancer growth” using casein is pretty impressive. Campbell is referring to a study he performed (Dunaif & Campbell, 1987). The study actually shows something different than what Campbell claims.

It shows that rats made sick with carcinogens who were fed a 20 percent casein diet for a full 12 weeks showed greater preneoplastic lesions (which usually precede tumor growth) than those who were fed less casein. Well, sort of. Actually, the rats that were fed a low-protein diet for the entire duration of the experiment didn’t fare much better, it turns out. That is a far cry from casein causing cancer.

The main problem with Campbell’s assertion is that it just doesn’t hold up in the test of the real world. In the real world, dairy consumption does not seem to contribute to cancer.

Sure, industrially processed, isolated casein fed in ridiculous amounts to lab rats for 12 weeks straight may not offer perfect protection against exposure to known carcinogens. But then if that provides proof that casein is carcinogenic, we might as well claim that water is carcinogenic, because I bet that the rats were given water, too.

Finally, Chris Masterjohn offers a critique of Campbell’s rat study citations, pointing out that in actuality, casein is protective against the effects of aflatoxin (the carcinogen used in the studies).

It turns out that in the Indian study that sparked Campbell’s interest, the rats exposed to aflatoxin and fed a 5 percent casein diet all died before the conclusion of the study. On the other hand, the rats fed a 20 percent casein diet were still alive.

Sure, they had neoplastic lesions, but then again, they were exposed repeatedly to a known carcinogen at insane and completely unnatural levels. And unlike the low-protein diet rats, the high-protein diet rats were still alive at the end.

Campbell makes the weaker claim that the statistical numbers that he used to generate his China Study results indicate that animal protein (including dairy) causes cancer. This is a subject that we’ll look at in more detail later in the book, but for now, let’s just address the dairy issue, specifically.

Denise Minger appropriately points out that Campbell neatly omits from his study the only populations in China that actually consume dairy. Of those groups, one stands out in particular because of the large amount of dairy the group consumes. The Tuoli receive more than half of their calories from dairy. And do they have increased cases of cancer? According to the numbers, no, they do not.

In conclusion, there is simply no evidence that dairy causes cancer. In fact, there is considerable evidence that dairy, particularly full-fat dairy, is protective. Vitamin D deficiency, which can be exacerbated by large amounts of calcium in the absence of dairy fat, does correlate positively with ovarian and prostate cancer.

So for those who stay indoors and don’t supplement with vitamin D, drinking large amounts of non-fat milk is probably a bad idea. But then again, so is eating a lot of broccoli, which is also a bioavailable source of calcium. The negative effects of too much calcium and not enough vitamin D seems to be offset by adequate dairy fat consumption.

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