What’s the Story With Dairy and Period Problems?

Dairy can cause period problems.

For some women, stopping normal dairy products can relieve period symptoms. But why?

In the latest episode of my podcast and YouTube video, I discuss the inflammatory effects of A1 casein and how a mast cell histamine response can drive period problems such as premenstrual mood symptoms, heavy bleeding, and pain.

Also available wherever you get your podcasts.


For some women, stopping normal dairy products can relieve period symptoms. A big reason is that (for some women) stopping normal A1 dairy can dial down a mast cell and histamine inflammatory response to the dairy protein A1 casein.

Welcome back to the podcast. I’m your host, Lara Briden, a naturopathic doctor and author of the books Period Repair Manual and Hormone Repair Manual. It has been a long time since my last episode; sorry about that—2023 was big for me.

For one thing, I went to Greenland. If you’re watching the video version of the podcast, this is a shot of me on a 12-day wilderness trek in Greenland. Going there had been my lifelong dream ever since I was a teenager, really. And I can’t quite articulate why except to say that everything is bigger in the Arctic. The land is vast, and the light is shimmering, and it’s truly like nowhere else. On the Greenland trip, we slept in tents, we swam in the fjords, we ate wild blueberries and took turns watching through the night for the polar bear who was in the area. I’m very grateful for the entire experience, and we did not encounter the bear, by the way.

Also, in 2023, I wrote my third book. It’s all about metabolic health and is coming in May, so stay tuned for more about that. Also, stay tuned for the food addiction episode I promised at the end of my previous episode but was not yet ready to record.

Instead, today, we’re going to talk about the dairy protein casein and its possible role in mast cell activation, histamine, and period problems. The first thing to understand is that I’m speaking specifically about A1 casein from Holstein Friesian cows. They’re the dominant dairy cow breed in North America, the UK, Northern Europe, Australia, and New Zealand, but they’re not the dominant breed everywhere. So, dairy from other places may not—and, in my experience, does not—cause the same inflammatory response. In some people (but not everyone), A1 casein from Holstein cows metabolizes in the human digestive tract to an opioid peptide called casomorphin or, specifically, to an inflammatory casomorphin called BCM7. There are other casomorphins that don’t come into this discussion. BCM7 can then cause inflammation via several mechanisms including by activating mast cells, which then release histamine and other inflammatory mediators.

Now. There’s no A1 casein in the dairy from goats, sheep, or various other kinds of cows, such as Jersey cows. In some places (including here in New Zealand), milk without A1 casein is referred to as A2 dairy because it has only A2 casein. Plus, there are other types of dairy proteins, including whey, of course, and those are present in all types of dairy. Fortunately, most people are fine with A2 casein and whey, and we’ll come back to whey in a few minutes. And many people—I would say at least half of people—are also fine with A1 casein because they do not metabolize it to BCM7. So they do not get an inflammatory histamine reaction. Variation between individuals is why there was such a diversity of responses to a recent survey I ran on my social media. I asked people if they had ever tried coming off dairy for period problems. And of all the people who said they had tried coming off dairy, not quite half said they felt better for it—which fits with my clinical experience, actually. Only about half of people seem to need to avoid A1 dairy.

So, how do you know if that’s you? How do you know if it’s worth trying some time off normal dairy? Well, first, you want to consider the nature of your period symptoms. So, avoiding dairy is not just a blanket treatment for any period problem. It can be specifically helpful for a few things, including hormonal acne; see episode 8 for more about acne. But today, I’m going to talk about how avoiding A1 dairy can be helpful for allergic-type or allergy-type premenstrual symptoms like fluid retention, hives, itching, headaches and nausea. Avoiding A1 dairy can also be helpful for premenstrual brain fog and anxiety because histamine is not just an inflammatory mediator; it’s also a stimulating, anxiety-causing neurotransmitter and potentially plays a big role in some types of PMS and PMDD. Finally, avoiding normal A1 dairy can be helpful for breast pain, period pain, and heavy periods because there are a lot of mast cells in the breasts and in the uterine lining.

According to an intriguing paper by Dr Tania Dempsey and other authors (the citation in the show notes), mast cell activation can cause heavy periods because mast cells release not only histamine but also heparin, which is a natural anticoagulant, which—by preventing the normal clotting mechanisms, can increase menstrual flow. To be fair, Dr Dempsey’s paper does not talk about avoiding casein as a natural antihistamine strategy. Instead, she looks at using antihistamine medication to lighten menstrual flow, which it really can do. I’ve seen that clinically. Seeing this research was a real light-bulb moment for me. I looked at it, and I thought, “Oh my goodness. Maybe that’s why coming off dairy can lighten periods.”

So, in short, it can be worth trying a few months off dairy if you have those symptoms I listed earlier— including heavy periods plus, if you have a history of childhood immune problems like recurrent tonsillitis, ear infections, or allergies. I always ask my patients about childhood immune problems, and I usually interpret them as early signs of an A1 dairy sensitivity in combination with, obviously, genetics and microbiome and other factors. Most people will outgrow childhood immune symptoms only to go on to develop adult symptoms like digestive issues, skin inflammation, and, of course, period problems, the topic of today.

In a 2023 paper called “Childhood asthma, allergies and risk of premenstrual disorders in young adulthood,” researchers linked food allergies in childhood to premenstrual mood symptoms in adulthood. They don’t actually say dairy is one of the main food allergies they’re observing, but I would say it has to be. The link to that paper is also in the show notes.

So, food sensitivities in general—and sensitivity to A1 dairy in particular—can potentially set you up for period problems. One of the mechanisms by which A1 dairy sensitivity will do that is by activating mast cells in the brain, breasts, and uterus— which then release inflammatory cytokines, heparin, and histamine, contributing to the symptoms mentioned earlier.

Of course, dairy is not the only activator of mast cells. Others include stress, alcohol, gut problems, and estrogen—which is why these histamine-type period problem symptoms track with the menstrual cycle. Symptoms typically worsen during the two estrogen peaks in the cycle, so just before ovulation and then midway through the luteal phase. Histamine-type period symptoms can also worsen near the end of the luteal phase when progesterone drops and you lose progesterone’s natural antihistamine effect.

So, complicate things even further, it might not just be mast cells. You could also be reacting to high histamine or amines in food itself, including… there can be amines in some dairy foods like aged cheese. Or you could have higher levels of histamine from food because you have low activity of a gut enzyme called DAO, which normally helps to break down histamine.

So, just to try to be clear: histamine from mast cells is mast cell activation syndrome and histamine from food, and the gut is histamine intolerance. And dairy can play a role in both and there’s a lot of overlap between those two conditions.

If you think your period symptoms might be at least in part from a mast cell reaction to A1 casein, the plan is to avoid all normal dairy— all A1 dairy continuously—as in, every day, not just during the bleed—for at least three menstrual cycles. That means avoiding all normal milk, yoghurt, and cheese. Butter, ricotta, and whey protein should be fine because they have very little casein. You can probably still have goat, sheep, buffalo, or A2 (e.g. Jersey cow) products. But not lactose-free dairy products because they still contain casein. And not low-fat dairy because that accomplishes nothing because dairy fat is good for periods. Depending on where you live, it should be quite easy to access goat, sheep and Jersey products. You could also try some of the plant-based dairy substitutes; just try to avoid products with added sugar, emulsifiers, or vegetable oil.

And the reason I recommend persisting for at least three menstrual cycles is because that’s how long it can take to get a good sense of whether it’s helping or not. After your third period, assess. How were your menstrual-premenstrual symptoms, for example? How was your period pain? And did your flow lighten?

And then there’s the question of, “Why did avoiding dairy help your period?” Was it really the A1 casein, as I’m saying? Or was it something else like whey? As mentioned, my clinical observation is that most people are fine with whey, whether that’s from a whey protein powder or a whey cheese like ricotta. But some people feel they do react to whey, and also, for what it’s worth, whey does increase insulin directly after eating it, but I don’t necessarily see that as a big problem.

Or was it the hormones in dairy, such as the naturally occurring growth hormone IGF-1? My understanding is that the levels of IGF-1 in dairy—all types of dairy—are relatively low compared to our normal baseline levels. So, I’m not sure how much of an effect it really has, IGF-1 has on the menstrual cycle. But we can all watch the research on that one.

Or was it a problem with lactose? It’s interesting because, of course, A2 milk does contain lactose, yet many people who think they’re lactose-sensitive or have been told they’re lactose-sensitive find they can tolerate A2 milk, suggesting the problem all along was possibly casein and not lactose. There’s also the fact by avoiding A1 casein, you reduce inflammation in the gut which can actually improve levels of lactase enzyme and improve lactose tolerance.

You may also be wondering if you can improve symptoms simply by switching to raw or organic A1 dairy—normal dairy. So, my experience is that the mast cell-histamine-type symptoms I’ve been discussing in this podcast cannot be improved by switching to organic or raw. Basically, because the A1 casein is still present in those milks. However organic milk is good for other reasons, such as being higher in omega-3 fatty acids compared to conventional milk. So, if you’re having organic milk and enjoy it, then that could be okay as long as you’re not also having these A1 casein histamine symptoms.

Importantly, there are lots of other ways to stabilise mast cells and reduce histamine and improve period problems. Examples include:

  • Antihistamine medication, as we saw in Dr Dempsey’s paper. It can work quite well to both lighten periods and relieve premenstrual mood symptoms.
  • Fixing the gut is another strategy, which usually means addressing SIBO. A healthier gut will dial down—potentially—that casein mast cell reaction, plus it can increase levels of DAO, the enzyme that helps to break down histamine.
  • Progesterone can relieve symptoms, in part, thanks to its natural antihistamine effects. Progesterone has other benefits for periods, obviously. And I’m referring here to natural or body-identical progesterone, not the progestins of hormonal birth control. So, you can see my other podcasts and writing to hear more about the difference between progesterone and progestins.
  • Avoiding alcohol can really help.
  • So can reducing stress because stress plays a big role in mast cell activation.
  • And finally, vitamin B6 can greatly relieve premenstrual mood symptoms—partly because of how it reduces histamine and partly because of how it boosts serotonin and GABA. There are some safety considerations for vitamin B6, which I discuss in episode 7 of the podcast, which is a deep dive into premenstrual mood symptoms, including all the other drivers or factors. It’s not just about histamine.

You might also want to check out episode 2, which is all about heavy periods and, again, about all the different possible causes of heavy periods. I do talk about dairy in that episode.

And if you want to know more about the science of A1 casein and its inflammatory casomorphin metabolite, see scientist Keith Woodford’s 2021 review paper titled “Casomorphins and gliadorphins have diverse systemic effects spanning gut, brain and internal organs.” The link is in the show notes.

Finally, tell me about your experience with dairy, either as a comment on the blog that’s associated with this episode or in my forum. I hope that’s been helpful, and thanks so much for listening. Please share and leave a review. And I’ll see you next time when I will finally tackle the topic of food addiction.

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