There's nothing like hearing about something that can effect so many of us....and diving into the literature to see what it's all about! 

The literature and subsequently doctors have reported on a recent study that found casein, a protein found in milk to the tune of 80% (1), to increase the rate of prostate cancer cells (2).

I also heard about this study after a friend presented a YouTube video of a doctor talking about it - so I was desperate to get hold of the full text to learn more! (Hello Alex!)

Now it doesn't sound good - most people hearing the headline would say: "Right, that's it, no more milk..."

And its not their fault - most people hardly have the time (and some the know-how) to read the full text to see what the scientists found and in what detail.

The study looked at prostate cancer cells, lung cancer cells, stomach cancer cells, breast cancer cells, normal kidney cells and this is the interesting part of the puzzle: normal prostate cancer cells. They treated them NOT with milk, but with casein, and wanted to see the effect it had on cancerous growth, in the cells effected by cancer and those that weren't.

Now the most important thing to point out here is that the study was not done into human beings - but rather OUTSIDE of the human body and in the labratory (in vitro) think petri dish. 

So what did they find?

The casein didn't effect any of the other cells negatively, however it grew the prostate cancer cells already effected by cancer by 228% and 166% respectively - just as the doctor had said in the YouTube video.

So the cancerous prostate cells grew in a lab when treated with casein...but that tells us nothing about living things - we need more information and need to study this into human beings before making any definitive decisions! The authors even say this in their conclusion.

So one year on from this study (and the aforementioned YouTube video) - further research was conducted into rats, and NOT funded by the dairy industry or any other industries for any cynics reading this! (3).  

So what did the rat study find?

It found that high milk consumption "did not promote progression of existing prostate tumors when assessed at early stages of tumorigenesis."

In other words, our little four-legged friends didn't advance their tumours by having milk. 

Now as it's accepted within the world of science - studies done into rats are not a reliable indicator for the fate of human beings, but terrific for creating a hypothesis (4).

The authors also point out that in the study that found the growth of prostate cancer cells by 228% and 166%  after being treated not with milk but with casein (the one the doctor was talking about on YouTube) - they used a super high casein concentration. Let's hear from the authors:

"However, these effects i) were obtained at extremely high casein concentration (1 mg/mL), ii) were not validated in vivo (in a living thing), and iii) only involved a single milk protein family out of the complex nature of ingredients constituting milk."

So in a dish - prostate cancer cells grow. But we don't live in dishes - we're living things. In rats, their cells that were effected by prostate cancer did NOT grow after milk consumption.

And unbelievably, the authors found a slight protective benefit to consuming milk for the rats with prostate cancer. Let's bring the authors in again: 

"For some parameters, and depending on milk type, milk regimen could even exhibit slight protective effects towards prostate tumor progression by decreasing the expression of tumor-related markers like Ki-67 and Gprc6a. In conclusion, our study suggests that regular milk consumption should not be considered detrimental for patients presenting with early-stage prostate tumors." 

Both Sides Of The "Milk Causes Prostate Cancer" debate

There's a lot of epidemological studies (looking at cancer and looking at what people consume, and drawing a link) suggesting an increased prostate cancer risk with increased milk intake (5-10). However not all have discovered such (11,12).

But epidemological data is NOT cause and effect....people get cancer from many different ways (many unknown) and most people do drink milk so of course it's always going to show up as something consumed by those who have cancer.

The truth is a cancer link is found for a lot of the foods we eat - but the risk is reduced once we look at in the context of the big picture, or a meta-analysis (gathering all studies together and drawing a conclusion). One study found cancer links in 50 randomly chosen common ingredients from recipes in cookbooks, with the conclusion stating:

"Associations with cancer risk or benefits have been claimed for most food ingredients. Many single studies highlight implausibly large effects, even though evidence is weak. Effect sizes shrink in meta-analyses."

But with this recent rat study, and the study the doctor was talking about on YouTube - we see that when we examine this directly, there's currently no cause for concern.

That's not to say that one day in human beings when we examine cause and effect...regular milk consumption MAY be found to increase cancerous cells in the context of the prostate. But this remains to be seen and studied. Based on the available literature, this does appear to be an unlikely finding - but I'm definetly NOT saying it's never going to happen! But on the other side of the coin, there are many benefits to milk - which I'll get to. 

But first - what does it boil down to? What's the "real world" advice for us all?

As the scientists from the rat study said above - "In conclusion, our study suggests that regular milk consumption should not be considered detrimental for patients presenting with early-stage prostate tumors."

This would naturally also go for us younger gym-going gentleman who are NOT effected with cancerous cells in our prostate. 

Moreover, here's 5 other findings into milk that have been discovered in the literature, and they are:

1.  "In terms of cancer risk, dairy foods have been reported as both protective and occasionally as harmful. The evidence that dairy foods can protect against cancer, or increase the risk of cancer is not conclusive. Overall, the proven health benefits of dairy foods greatly outweigh the unproven harm" (14).

2. Whey and casein (found in milk obviously) can protect against colon and breast cancer (15).

3. Whey proteins may also reduce your cancer risk by strengthening hormonal and cell-mediated immune responses (16,17).

4. Whey proteins have also been observed to bring about anticarcinogenic activity (18)

5. Further to reference 14, the authors of the review add:

"There is certainly no evidence that milk consumption might increase death from any condition....Moreover, a decisive and conscientious consideration of the relevant literature reveals that the probable harmful effect of milk and dairy product consumption related to cancer is dose-dependent. Therefore, harm for normal people could only occur with absolutely excessive and indiscriminate consumption rather than regular moderate daily intake..."

And no, this research wasn't funded by the dairy industry.

The verdict?

Enjoy dairy until further notice! And if you still want to omit from your diet, go for it.

The choice is complettely yours - but there's the current evidence we have!


"Stay Fit, Stay Flexed!" 



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(2) Park SW, Kim JY, Kim YS, Lee SJ, Lee SD, Chung MK. A milk protein, casein, as a proliferation promoting factor in prostate cancer cells. World J Mens Health. 2014 Aug;32(2):76-82. doi: 10.5534/wjmh.2014.32.2.76. Epub 2014 Aug 26.

(3) Bernichtein S, Pigat N, Capiod T, Boutillon F, Verkarre V, Camparo P, Viltard M, Mejean A, Oudard S, Souberbielle JC, Friedlander G, Goffin V. High milk consumption does not affect prostate tumor progression in two mouse models of benign and neoplastic lesions. PLoS One. 2015 May 4;10(5):e0125423. doi: 10.1371/journal.pone.0125423. eCollection 2015.

(4) Akhtar A. The flaws and human harms of animal experimentation. Camb Q Healthc Ethics. 2015 Oct;24(4):407-19. doi: 10.1017/S0963180115000079.

(5) Chan JM, Stampfer MJ, Ma J, Gann PH, Gaziano JM, Giovannucci EL. Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study. Am J Clin Nutr. 2001;74:549–554. 
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(10) Gao X, LaValley MP, Tucker KL. Prospective studies of dairy product and calcium intakes and prostate cancer risk: a meta-analysis. J Natl Cancer Inst. 2005;97:1768–1777. 
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(16) Parodi P. 2008Milk lipids: their role as potential anti-cancer agentsSci des Aliments 28:4452.

(17) Bounous G. 2000. Whey protein concentrate (WPC) and glutathione modulation in cancer treatment. Anticancer Res 20:4785–92.

(18) McIntosh GH, Royle PJ, Le Leu RK, Regester GO, Johnson MA, Grinsted RL, Kenward RS, Smithers GW. 1998. Whey proteins as functional food ingredients? Intl Dairy J 8:425–34.