Does Dairy Cause Breast Cancer?

Dairy is a common target of nutritional fear mongering. It’s also one of the most highly politicized nutrition topics in the United States. Pro-dairy groups will tell you that you must eat dairy for good health. Anti-dairy groups will tell you that you must avoid dairy for good health. Who’s right?

The truth? Somewhere in the middle.

This is because the connection between dairy and health is not black and white. Dairy may be helpful for reducing risk of some health threats, yet it may be implicated in increasing the risk of other diseases. If someone issues a blanket statement about dairy and health, they simply are not telling the truth. The science on dairy and health does not support that dairy is always good, or always bad.

Can dairy and breast cancer be studied accurately?

Unfortunately, the gold standard of research – a double-blinded, placebo-controlled trial – isn’t available for dairy and breast cancer. It’s nearly impossible to randomly assign people to consume dairy or not consume dairy, have them stick to this dietary regimen faithfully, and follow them for the decades required to see how many people in each group get breast cancer.

Never mind that you can’t “blind” people to the intervention. If someone is assigned to drink milk, they know it. There isn’t a good placebo – or a non-dairy milk – that would fool anyone into thinking they are drinking milk when they aren’t. Ditto for cheese and yogurt. So it’s unlikely that we’ll get this type of evidence anytime soon.

Fortunately, there are dozens and dozens of observational studies on dairy and breast cancer. And while no single observational study can prove cause and effect, when we have a lot of these studies to consider, we can look for a pattern.

A great example is smoking and lung cancer. Even though we don’t have a controlled clinical trial on smoking and lung cancer, the observational studies all point the same way.

And about breast cancer?

How do dairy and breast cancer stack up? It turns out that dairy is, if anything, slightly protective against breast cancer. One large meta-analysis – a type of study that combines data from previous studies on the topic – found that women with the most dairy in their diets had about a 15% reduced risk of breast cancer.

However, other large observational studies and research reviews have found that dairy is neither protective against, nor increases the risk of, breast cancer. In essence, it is neutral.

To sum it all up, if dairy foods truly had a strong connection with breast cancer, the results of all of this observational research would consistently point in that direction. This isn’t what we see, which means there probably isn’t a strong connection between dairy and breast cancer risk, one way or the other.

The Take Home Message?

If breast cancer is your concern, dairy is pretty much a non-issue. If you enjoy dairy, have dairy. If you don’t like dairy, don’t have dairy. You may have other reasons for wanting to avoid dairy, but don’t let someone sway your decision by convincing you that dairy causes breast cancer.

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4 responses

  1. Interesting post! I wonder about the results of the meta-analysis, though, and the studies it analyzed. Specifically, I suspect that (1) dairy is displacing some other even less healthy food in women’s diets and (2) women are so deficient in vitamin D that the amount added to dairy is enough to outweigh some of the detrimental effects of consuming milk past infancy. (Given the biochemistry of dairy, I’d be surprised if it didn’t promote excess cell growth.)

    Also, for women who already have breast cancer, high-fat dairy CAN be dangerous. One 2013 study found that consuming as little as 1 serving of high-fat dairy per day increases the risk of dying of breast cancer by 49% for women with the disease. So I wouldn’t necessarily say dairy is a safe food for those concerned with breast health, although the jury may still be out. (http://www.ncbi.nlm.nih.gov/pubmed/23492346)

    Regardless, I applaud you for taking on the topic! A thorough, thoughtful post. (So woefully lacking in the arena of nutrition!)

    • Meta-analyses do have their flaws, though the main point is that the bulk of the studies agree about the fact that dairy is likely neither a harm nor a benefit when it comes to breast cancer risk.

      I’m aware of the 2013 study showing an association between high fat dairy and risk of recurrence, but the issue with this is that this is the FIRST observational study to show this finding. With dairy in general, there are at least a dozen studies showing no increased risk.

      Because diet studies are almost always, by nature, observational and at the least, an unblinded trial – it’s pretty tough to assign a group to a specific diet and not have them realize they are in the intervention group – you need to consider many studies together. No single observational study, and the study you cited is observational, can really give enough information to understand whether the relationship is causal.

      To be fair, even a group of observational studies can’t prove cause and effect (only correlation), but that is why we look to large groups of observational studies to see if a pattern emerges. With dairy, no clear pattern points to increased OR decreased (primary) risk for breast cancer. With the number of studies that exist, if there were a strong association, there would be a pattern, but there isn’t a clear one.

      Time will tell if the high-fat dairy and increased risk of breast cancer recurrence holds up. However, I do agree with you that along the lines of the precautionary principle, if a woman has a history of breast cancer, cutting out high fat dairy certainly isn’t a bad idea.

      And in all honesty, I’m no huge fan of dairy. I don’t believe data support that dairy is the dietary evil that many people say it is. But I also don’t think there’s any reason to have dairy in the diet. The American diet is heavily weighted toward dairy, and people receive misinformation about how important dairy is for bone health, for example. There’s just no reason a person has to have dairy in the diet.

      A healthy diet with NO dairy is a great option, and I assure people that, “No, your bones won’t crumble without dairy!”

      But I really aim to provide honest, accurate, research-supported information. So while I’m not a fan of dairy, I also want to present information that is as unbiased by personal belief and food politics as possible

  2. I went to your blog from the ON DPG EML, this is a very helpful blog post. I’m doing a report for dietitians on the topic of IGF-1, dairy and cancer. Reading research is my least favorite thing to do, and I get very confused. I appreciate your explanation of types of studies, as I never wanted to get my master’s degree with all the research. I definitely agree with your opinions on dairy, and I try to provide unbiased opinion for patients. I’ve considered giving up all dairy myself as I never drank milk but I can’t give up cheese!

    • Glad to help out. I think there are a lot of good reasons to give up dairy, from animal cruelty issues to climate change. Dairy takes a lot of energy and water to produce compared with plants! Regarding cheese, I have to say that vegan cheese has come a long way, just in the last year or two. Prior to quite recently, vegan cheese was pretty awful. It has a terrible reputation, because it truly was terrible! Now, there are some really great options on the market, and where I live, the first vegan cheese shop just opened up! Check out the pictures in this article. My husband and I tried it out last weekend and we are complete converts to the vegan cheese side. We had that panini they mention in the Portland monthly article. It was amazing. They have this aged black garlic cheese that is truly divine. As for vegan cheese in the grocery store, I like Chao cheese, which is widely distributed now. I like the creamy original. Makes a great grilled “cheese” sandwich. I’ve been a vegetarian for 20+ years, and in the last 2 years, I’ve moved to completely vegan. I have no regrets! One last place to check out vegan cheese brands is Veg News.

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