Recently, I interviewed Dr. Meg and we discuss the basics of histamine and its metabolism, symptoms of histamine intolerance, the connection between histamine and thyroid health, the impact of gut health, hormonal balance, and the microbiome on histamine levels, practical tips for managing histamine intolerance, and more. If you would prefer to listen to the interview you can access it by Clicking Here.
Dr. Eric Osansky:
I am super excited to chat with Dr. Meg Mill, as we will be talking about histamine and tying it into thyroid health. A lot to talk about when it comes to histamines.
Let me dive into Dr. Meg’s impressive bio here. Then we will start our conversation. Dr. Meg Mill is a Pharm.D. and certified functional medicine practitioner with over two decades of clinical experience. She is also a bestselling author, podcast host, summit host, and sought-after corporate wellness speaker.
Her virtual functional medicine practice has transformed the lives of hundreds of clients worldwide by connecting the dots between the diverse, unexplained, and often overlooked health struggles such as migraines, gut issues, chronic fatigue, skin reactions, anxiety, or allergies. She uses her EAT Method to uncover and resolve the underlying connections, whether it’s histamine intolerance, hormone imbalances, gut dysfunction, or MCAS (mast cell activation syndrome). Welcome, Dr. Meg.
Dr. Meg Mill:
Hi! Thank you so much for having me.
Dr. Eric:
It is a pleasure to have this conversation, talking about histamine. So many people have histamine imbalances. Many of these people don’t know they have histamine imbalances. Let’s first dive a little bit more into your background. How did you start helping people with histamine intolerance as well as MCAS?
Dr. Meg:
I actually have it myself. I didn’t realize it for so many years. I was the kid who had tons of allergies. I remember my parents actually redid a dresser for my room, had it painted, and I couldn’t keep my clothes in the dresser after it was painted because it would make me so sick. “My clothes make me sick.” My mom was like, “Why? What’s wrong with your clothes?” There are all these clues for people over time.
What I started to find was that histamine issues, MCAS, they are growing more. They are connecting a lot of different symptoms. I am saying I was someone who had allergies. I was highly reactive. Then I started having GI issues, where I couldn’t even eat anything. I was having so much stomach pain. I jumped around from gastroenterologist to gastroenterologist and was told I was fine, that I was the picture of health. Then I got anxiety, which led to insomnia. All of these things that started happening and building on each other seemed to me unrelated, but they all have this common link, which is histamine.
Sometimes, when you’re looking at it through the histamine lens, you start to connect all of these dots and think, “My anxiety and my allergies and my gut issues, they don’t all seem related.” But when we are looking at it from that point, if we can get the histamine to be lower, to get it under control, a lot of things will clear up.
I was having a lot of my own personal health issues. Then I also was not getting any answers and being told I was fine. Here I am in the health space, and I can’t get answers for myself, which led me to functional medicine.
I actually made a career change. I got certified in functional medicine and opened a functional medicine practice. Now I help people all over the world get to the root of their mystery health conditions. Looking at the connections of all of these different symptoms and how your body builds on the connections. We can just unwind it to get you feeling a lot better.
Dr. Eric:
Histamine issues can definitely be complex. It’s safe to say some people watching this are familiar with histamine. There are some people who aren’t familiar with histamine. That is my next question. For those who are asking what histamine is, can you explain what it is? We will go deeper. We are not going to get too much into MCAS. Or we could. It depends on you actually. I want them to know the basics of histamine and histamine metabolism.
Dr. Meg:
Histamine is the new cortisol. When you think of cortisol, you think of bad. When you think of histamine, you think of bad. But they do have purpose in your body.
Histamine is what we call a biogenic amine. When your immune system detects an allergen or invader, histamine is released primarily from your mast cells or basophils as part of your immune response.
In your immune system, we have two different systems. We have your innate immune system and your adaptive immune system. The mast cells are part of this innate immune system, so they are ready to go. They are ready to fight. They are not selective. Let’s get this.
One of the things they release is histamine in order to do things like increase permeability of the blood vessels, which allow immune cells to reach the area more quickly. Histamine helps with immune defense.
It helps with regulating your gastric acid secretion to break down food and aid in digestion.
It affects your neurotransmitters. It can affect serotonin, norepinephrine, acetylcholine. It can be involved in your wakefulness, your alertness, your cognitive function, your mood.
It’s a part of the allergic response. That’s what most of us think of when we think of histamine. It can also cause broncho restriction. It constricts your airways to prevent harmful airborne substances to enter too deep into the lungs.
And it actually also creates an inflammatory process. It actually creates inflammation. It recruits immune cells to the site of infection or injury through this increased vascular permeability and blood flow to create this inflammatory response.
However, when it’s excessive or not regulated, it can lead to chronic inflammation. That is when we start to get a lot of these symptoms and problems.
Dr. Eric:
I’m glad you mentioned an excess. Histamine by itself isn’t a bad thing. It’s important. We need histamine, just like inflammation by itself is not bad. It’s when it becomes excessive and chronic.
Let’s talk about histamine, especially the metabolism. There are different enzymes: diamine oxidase (DAO). I’ll let you take over because you are the histamine expert.
Dr. Meg:
Let’s use a bucket analogy. Think of your body like a bucket with holes in the bottom of the bucket. You’re filling it up, and it’s draining. You’re filling it up, and it’s draining. We keep doing that. Everything is fine. You feel good. You’re moving through life.
When we start to have these symptoms of histamine intolerance, we start to have one of two or both things happen. We are either pouring too much water into that bucket, and it’s overflowing. Or we plug the holes in the bottom of the bucket. Or both.
When we plug the holes, it fills up too much. When we fill it up too much, we fill it up too much. If we get this overflow, that is when we start to have all of these symptoms.
We will talk about what plugs the holes. You break down histamine by two different pathways in the body. One is diamine oxidase, which you mentioned. The other one is histamine n-methyl transferase (HNMT).
The diamine oxidase is the main enzyme responsible for breaking down histamine from foods in our intestinal tract. We will get into some of these histamine-producing foods that are often healthy foods. That can be really confusing sometimes because things you think are eating for certain purposes to help your body can also be high in histamine and create some of these problems.
We want to look at some of the other reasons that diamine oxidase can become compromised. First of all, people can have genetic variations. I am one of those people. I told you, I had some of these symptoms forever. Generally, they build because even if you have the genetic variations, we’ll get into how gut health can play a huge role. If everything is functioning properly, we can usually overcome some of the genetic variants. You can have genetic predisposition not to process histamine as well.
The main thing we see are imbalances in your microbiome. We need to have certain gut bacteria that can help us break down the histamine. Then we have bacteria that actually inhibits the DAO. We can have histamine-producing bacteria. We can have mast cell-activating bacteria. We can also have things start to happen that compromise this enzyme function.
Once we have compromised enzyme function, then we can’t break down histamine very well. Everyone pretty much knows about lactose. There are certain people with lactose intolerance. When you have lactose intolerance, you can’t eat dairy because you have problems breaking it down. It’s a very similar enzymatic reaction.
When we are eating histamine, we need diamine oxidase to break down those foods, so they are not affecting us. We can also see that once we start to get intestinal permeability or leaky gut, we can also get chronic inflammation. This inflammatory response can also downregulate the regulation of diamine oxidase, so the body can shift more toward resources for managing inflammation. Then it can further exacerbate histamine-related issues. We are seeing some of those things happen.
We can also see certain nutrient deficiencies. We know that certain nutrients are required to make diamine oxidase. Things like Vitamin B6, copper, and Vitamin C can also be a problem. I know I keep coming back to the gut, but sometimes, even if we are eating all those nutrients, but we can’t digest or absorb them, we may not really be getting the full effects of those.
We are looking at all of these things together to look at how well are you really breaking down histamine?
Another one that might be surprising to you is fluctuation in hormones. Estrogen can cause the mast cells to release histamine. Estrogen can also influence diamine oxidase activity. Higher levels of estrogen can lead to a reduced diamine oxidase activity.
Progesterone actually helps increase diamine oxidase.
When we start to become estrogen-dominant, having high estrogen to progesterone, we can also see hormones creating an imbalance that can affect it. That can play a role in one pathway.
We have another pathway, which is HNMT. You have probably heard of methylation at this point. Everyone is talking about that now, which is good. We are starting to see that we need methylated B vitamins. We need to be able to methylate in order to break down histamine.
Histamine is methylated into HNMT. It goes through this methylation process and is excreted in the kidneys.
One thing I just want to clarify is a lot of people are talking about MTHFR. A lot of people are talking about methylated B vitamins, which is great. That is not the only thing that is affected in this pathway. Sometimes, we actually need to look further down the pathway.
We can also see an MAO variant, monoamine oxidase, affect this pathway. You may need a riboflavin, B1, or B2. You can push some methylated B vitamins. If you feel worse, it might be because you have blocks further down that pathway. That’s something to keep in mind.
We also need certain vitamins and nutrients for that. We mentioned folate, B12, B6. Different nutrient deficiencies can play a role. Sometimes, we see poor liver function affecting the methylation pathway. Some drugs. We want to make sure that we really have those pathways open.
Dr. Eric:
I’m glad you shared that. I will summarize. There are two main enzymes that break down histamine. DAO, diamine oxidase, is the main one. HNMT, which is the other enzyme that can help with that. There are different factors that can influence these enzymes. You mentioned the importance of the gut microbiome and of course genetics. When you talk about genetics, it’s not just MTHFR. With HNMT, you mentioned methylation. You mentioned MAO.
One thing related to that is COMT. You also mentioned that COMT is involved in methylation. But you mentioned, and I am going down a rabbit hole here, estrogen can inhibit DAO. The COMT also plays a role in estrogen metabolism as well. If someone has a genetic variation in the COMT enzyme, can that also affect the breakdown of histamine at all?
Dr. Meg:
It can. A lot of these pathways we are seeing are interconnected. That is one of the main points of functional medicine, right? When you’re talking about something, you’re looking at this one thing, but I’m always telling people, this relates to that, and this is connected here. They’re all connected to each other in various ways. When we look at this, we are looking at it from a whole person perspective. We are looking at how each one of these pieces, your lifestyle, your genetic factors, all of your levels are playing a role into what’s going on in a unique way for you. A lot of different things can play in when looking at some of these pathways and breaking down.
Dr. Eric:
What are some of the more common symptoms people will experience when having a histamine intolerance?
Dr. Meg:
I think this is a tricky one for people to understand. We think of nasal congestion, sneezing, asthma, difficulty breathing. Then you’re thinking about highly reactive, maybe hives, rashes. Those all can be. But we can also see headaches and migraines. The people I work with with migraines, a high majority of people have histamine intolerance. We see fatigue, heart palpitations, dizziness, anxiety, depression, difficulty concentrating, PMS, irregular periods, flushing, joint pain, insomnia, high or low blood pressure. As you can see, there is a lot of different symptoms.
A lot of digestive difficulty. There is more and more research with IBS and histamine intolerance and the effect of mast cells. A lot of IBS symptoms are also coming from histamine issues, too, that are playing a part.
I think that’s one of the messages I’d love to hit home in this episode. Like we’re saying, it’s more than just allergies. When you’re talking about your thyroid, let’s say you could overlap some of these symptoms with thyroid. You can overlap some of these symptoms with a lot of different things. It’s really looking at what lens are you looking at it through? Could histamine be a part of this picture?
Dr. Eric:
Speaking of thyroid, would some of the relationships between histamine and thyroid that you’re aware of?
Dr. Meg:
Thyroid hormone, particularly T4 and T3, can influence the metabolism of histamine. We do want to make sure that we have proper thyroid function to help maintain balanced histamine levels. They can play a factor in the activity of the diamine oxidase and HNMT. Looking at making sure your thyroid levels are balanced.
We are talking about histamine intolerance as gut health. When we are looking at Hashimoto’s and thyroid, the leaky gut, gut health is really critical. We want to make sure that we are optimizing our microbiome, that we are looking at what good bacteria we have, what overgrowth we have, and really getting a balanced microbiome in order to optimize this function.
Also, we are going to talk more about- I can bring this up a little bit here, too. The mast cells. We sometimes can see mast cells present in the thyroid gland. Their activation can affect thyroid function.
We brought up mast cells. Histamine is released from mast cells. Some people can get what’s called MCAS. When we’re talking about filling the bucket, one of the things that starts to fill that bucket is MCAS.
When we start to have this, our body starts to go into what we call a cell danger response. We start to feel like our cells are under attack. Once we go into the cell danger response, we start to react to everything. If someone has MCAS, they are more likely to be someone who is reacting to a lot of different foods. Sometimes, we can react to heat, smells, sounds, EMFs. We start to be more hyperreactive. Our mast cells almost are getting angry, and they are firing for no reason.
An example I like to use here is if you’re smelling a rose, and you’re touching a stove at the same time, every time you smell the rose, you touch the stove. This beautiful smell is associated with this pain. Then the person tells you, “Smell the rose, but take your finger off the stove.” You can smell the rose and still feel that pain because your body is still associating that it’s in danger. It’s associating that the smell of that rose is going to cause you pain even though that’s not there anymore.
That’s what starts to happen in MCAS. Our body is starting to release these mast cells even when it’s not necessary, when we’re not in danger. In that case, we need to look at what is the root cause? What is happening to your body that is causing this excess release of mast cells?
We sometimes also need to work on nervous system rewiring, working on bringing our body back into that parasympathetic nervous system to feel calm, to feel safe, to be able to do some different exercises to rewire our body and feel safe in where we are.
Dr. Eric:
Not everyone who has a histamine intolerance has MCAS, correct? That’s more advanced, you would say? As you explained, if you have an abnormal amount of mast cells, and things go a little bit haywire.
Dr. Meg:
Yes, exactly. Not everyone who has histamine intolerance has MCAS. A lot of people that have MCAS will have histamine intolerance because one of the chemicals released from mast cells is histamine. One of the major symptoms of that are histamine issues.
You can just have simply an inability to break down histamine and maybe are putting too much histamine in your body with the inability to break it down well. All we really need to do is help you break it down, help you rebalance your gut microbiome through the lens of histamine intolerance. Look at some of these specific things and make sure some of these pathways are open. We can create balance very easily.
Dr. Eric:
Is there a way to differentiate the two? I don’t know if you officially diagnose histamine intolerance by looking at histamine and looking at DAO. I know there are ways to do that, or if it’s more looking at the whole picture and the symptoms. Similar with MCAS. Are there markers that you look at on a blood test or elsewhere?
Dr. Meg:
Yes. There are diagnostic criteria for MCAS. You have to do certain testing a few days in a row. There is often urine testing. There are more diagnostic criteria. It’s hard to do. A lot of people aren’t actually always getting the diagnosis. They just can feel the symptoms.
With histamine intolerance, we can test histamine levels in the blood, so that is a place to start. I personally don’t find that the end-all be-all marker because I see a lot of people with histamine issues who aren’t necessarily showing high blood histamine or DAO levels on a blood test.
I personally like more of the diagnostic criteria. We do stool tests. We look at the microbiome. We look at some of the different factors to see what the person needs.
I think that’s another frustrating feature of people who have this issue. Sometimes, even the testing isn’t showing up as something that is conclusive. You feel like, “I’m having these symptoms. I don’t feel well.” Everyone is saying, “You’re fine.” It’s not so clear. Listen to your body. If you’re saying, “Okay, I do have some of those symptoms. I do have a cluster of more than one thing. I want to see what’s going on. I do feel like I’m more reactive.” Listen to yourself, and start thinking of this.
It’s going up and up. We are seeing more and more cases. It’s becoming more mainstream because more people are really experiencing it than ever before.
Dr. Eric:
It’s a good point. Even if you are able to diagnose histamine intolerance or MCAS, you still need to address the cause of the problem. You mentioned that you do stool testing. You also mentioned earlier that you do things to balance the parasympathetic nervous system and some rewiring. People still want to have an answer. If they have type 2 diabetes, insulin resistance, it’s nice to see that on a blood test. When it comes to histamine intolerance, they may or may not get the answer. Either way, you want to do things to address the cause.
You mentioned earlier IBS. I don’t know if this still holds true, but I know at least a few years ago, there is an overlap between SIBO and IBS. Not all cases of SIBO are IBS. Maybe it’s a percentage. I guess there is that overlap with histamine intolerance and SIBO. The question I’m trying to ask is: When you see people with SIBO, a lot of those people then do have histamine intolerance? Or is that something that you see in a lot of SIBO patients?
Dr. Meg:
Yes, there is three different ways. Great question. First of all, when you start to have SIBO or IBS, you have a disruption in the mucosal layer of your gastrointestinal system. That is where diamine oxidase is produced. When we start to get this imbalance, we start to potentially have a compromised function of diamine oxidase. That’s one bucket.
We also know there are certain bacteria that are histamine producing. We have things like certain forms of Lactobacillus, Morganella, Pseudomonas, Citrobacter, Klebsiella. We have certain bacteria that can actually be histamine-producing and be behind some of these triggers on their own.
I am going to tell a side story because I think it’s very interesting. I worked with a man who had Urticaria, itching so bad for 20 years. He had to take hydroxyzine every day, which is a prescription antihistamine. It makes you very drowsy. As soon as it would start to wear off, he would just full body itch. He would have to take another one. He was getting shots. He had been to so many different doctors.
He had no GI symptoms. I said, “I want to do a stool test.” He said there was nothing wrong with his gut. I said, “Bear with me.” He had really high levels of Morganella. That is a histamine-producing bacteria. We treated the Morganella. Within 3-4 weeks, his itching was gone.
I think it’s such a profound story. It’s showing that 20 years of this really severe problem that had nothing to do with his gut health in his mind was really a histamine issue from some of these microbes. They are very powerful. We sometimes don’t realize that. I wanted to give you some context around some of the things that can be going on that you’re not even realizing from the microbes.
The third bucket is when we have SIBO, when we have a parasite, when we have H-pylori, when we have some of these invaders, that can be a root cause. “I have to create an immune response. I have to fight this invader all the time.” That’s stimulating your immune system. If you’re sensitive in your immune system, you can be releasing more mast cells to degranulate and create more histamine, more mast cell issues.
There is three different ways. All of them can be playing into this dynamic.
Dr. Eric:
All right. You gave the example of Morganella, but if you have other imbalances, like H-pylori or parasites or candida overgrowth. How about SIFO?
Dr. Meg:
Yes.
Dr. Eric:
When people are aware they have histamine intolerance, or they suspect it, some people just eliminate foods higher in histamine. That could in some cases make a big difference in the symptoms. It’s not addressing the cause of the problem, but do you still have people do that while they are addressing the cause of the problem, to avoid those foods, to do the low-histamine diet?
Dr. Meg:
I think it’s a very good tool to use. I love how you said that. I think people can get really caught up in the low histamine diet and the nuances and start to feel like this is how they need to live. I want to stress that’s not the end-all be-all. It’s not just stop eating all histamine foods forever. It can be a really good resource for you to start.
We want to start looking at different kinds of foods. We know there are certain foods that are high in histamine, such as cheeses, fermented foods, cured meats, alcohol.
We are talking a lot about gut health here. If you are looking at a generalized protocol for gut health, fermented foods and bone broth are generally on those protocols. We know they support the microbes and are good in general, but not for people with histamine intolerance. You just have to be careful that when you’re looking at this, you’re doing it through this lens. That can be very confusing. You might be stimulating some reactivity in yourself.
We also can see histamine liberating foods, like strawberries, tomatoes. We can have foods that limit diamine oxidase. Tea is a good example of that. Caffeine can block diamine oxidase.
The other interesting component here is that when it comes to this freshness count, you can actually have issues with histamine from cooked meats. If you’re a meal prepper, you might want to flash freeze. We have a lot of people have issues with leftovers because histamine can grow in cooked meat. Always make sure you are eating more fresh foods than leftovers or canned products.
Dr. Eric:
That makes sense. Be careful about some of the foods. Bone broth and fermented foods, you’re right. They’re healthy foods, but if someone has histamine intolerance, it could cause other problems from a symptomatic perspective. Also, you mentioned increased inflammatory pathways as well?
Dr. Meg:
Yes.
Dr. Eric:
Okay. Supplements. Just like how eliminating foods can help but not fix the cause of the problem, same things with supplements. There are certain ones like quercetin or DAO. What are your thoughts on those?
Dr. Meg:
I think they’re great tools. We want to calm down the mast cells. We want to reduce the histamine load. While we’re working on the root cause, I do think finding relief is really important.
You can get the DAO enzymes. I like some combinations of the quercetin with some other bromaline and nettles. There are different things we can put together that really are effective to bring some of these symptoms down. They can be very helpful for a lot of people.
Dr. Eric:
Gut microbiome, stress, adrenals. You mentioned nutrient deficiencies. Having healthy hormones because estrogen dominance can inhibit DAO. You mentioned the thyroid and the importance of having a healthy thyroid. A lot of different factors out there.
What would be the first steps people should take for someone who is thinking they might have a histamine intolerance? Should it be working with a practitioner like yourself? Are there things they can do on their own to get started?
Dr. Meg:
I would say start with the low histamine diet. I have a handout that lays that out nicely. A lot of low histamine diets out there maybe are inaccurate or confusing. I will give that to you as a resource. If anyone wants to go to that, it’s a lot of information on histamine and foods. You can follow that. It’s nice to have a road map in what to do. Start with this low histamine diet.
If you’ve done that and are still having issues, or if you don’t want to stay on this low histamine diet forever, people just do that alone for too long, and they start to react to foods when they start to put them back in. Then work with a practitioner to get to the root and put some of these pieces together. If you do, you can see a dramatic difference in the way you feel.
Dr. Eric:
You have a summit coming up. Before you talk about the summit, where can people find out more about you, like your website? Anything else you want to share?
Dr. Meg:
My website is MegMill.com. I do free discovery calls. If you want to learn more information, I’d love to get on the phone with you and talk through what you’re going through. You can book that on the website.
I am on Instagram @DrMegMill. I also have a podcast called A Little Bit Healthier, where we talk about all different health topics. I’d love to see you over there.
I’m really excited about this summit. It’s going to have so much great information. I’ve spent the last eight months working on this. There are over 50 experts in this field. We are going to talk about histamine intolerance, mast cells, and all of the different ways it can affect you.
It’s a free event, June 18-24. It’s with DrTalks. Go to DrTalks.com. Just sign up, and you can watch about 50 hours of education for free. That’s a great place to start. We will put a lot of these connections together and give you some great tangible tips.
Dr. Eric:
That’s going to be awesome. Check that out. Check out her website and podcast. Thank you so much. You shared some great information about histamine intolerance and MCAS. Looking forward to the summit as well.
Dr. Meg:
Thank you so much. Thank you for having me.