Does Tea Block DAO? The Truth About Tea and Histamine

As I'm working through some courses on MCAS, I keep stumbling upon people saying that tea blocks DAO, so drinking it with food can be risky. DAO is the enzyme that breaks down histamine in the gut, so anything that interferes with it would matter. Yet some of the compounds in tea seem to be mast cell stabilizing. So off to PubMed I go!

What DAO Actually Does

Like I said above, DAO (diamine oxidase) is one of the main enzymes responsible for breaking down histamine, especially in the gut. When DAO activity is low or overwhelmed, histamine can build up and contribute to symptoms like:

↣ headaches

↣ skin flushing or itching

↣ digestive issues

↣ heart palpitations

↣ anxiety

So it makes sense that people are concerned about anything that might “block” it.

Where the “Tea Blocks DAO” Idea Comes From

Tea, especially green and black tea, contains compounds called polyphenols (like EGCG, a very popular one). Here’s where things get a little messy:

↣ Polyphenols can interact with enzymes in lab settings

↣ Some polyphenols can bind minerals like copper

↣ DAO is a copper-dependent enzyme

And somewhere along the way, that turned into: “That means Tea inhibits DAO”

The problem is… that leap skips a few important steps.

What the Research Actually Shows

Here’s what we do have evidence for:

1. Tea can reduce iron absorption

Tea polyphenols (tannins) can bind non-heme iron and reduce how much you absorb.

This is well-established in human research.

2. Tea polyphenols can bind metals in lab settings

Compounds like EGCG can interact with metals like copper in vitro.

But this doesn’t automatically translate to meaningful effects in the body.

3. Tea may actually lower histamine in other ways

This is the part that often gets overlooked:

↣ EGCG has been shown to reduce histamine production

↣ Tea compounds can help stabilize mast cells (which release histamine)

So instead of increasing histamine, tea may actually help reduce it in some cases.

So… Does Tea Inhibit DAO?

At this point, there is:

✖ no strong human evidence

✖ no clear enzyme kinetics data showing meaningful inhibition

✖ no consistent inclusion of tea in scientific lists of DAO inhibitors

So the most accurate answer is: We don’t have good evidence that drinking tea significantly inhibits DAO activity in the body.

Why Some People Still React to Tea

If tea doesn’t reliably block DAO, why do some people feel worse when they drink it?

There are a few more likely explanations:

↣ caffeine stimulating the nervous system

↣ sensitivity to plant compounds (like salicylates or phenols)

↣ underlying gut issues

↣ individual differences in how histamine is processed

So, a reaction doesn’t automatically mean DAO is being blocked, it could be for any number of reasons.

A Practical Approach

If you’re dealing with histamine symptoms, here’s a more evidence based way to think about tea:

↣ You don’t need to automatically eliminate it just because of DAO concerns

↣ If you’re taking iron (or possibly copper), it’s smart to separate tea by 1–2 hours

↣ Pay attention to your own response instead of relying on blanket rules

The Bigger Picture: Histamine Issues are More Than DAO

Histamine issues are rarely caused by one single enzyme.

They usually involve a combination of:

↣ gut health

↣ immune system signaling

↣ nutrient status

↣ nervous system regulation

↣ genetic differences in enzyme function

Focusing only on DAO can keep you stuck restricting foods without addressing the root cause.

So, it seems tea isn’t the histamine villain it’s often made out to be. For some people, it’s completely fine. For others, it’s a trigger, but not for the reasons they may have thought!

Want to Go Deeper?

If you’re trying to figure out your histamine patterns, guessing your way through food lists only gets you so far. This is exactly what I help clients take a shortcut.

Inside my Histamine Discovery Panel, I use the Fluids iQ Intestinal iQ to look at:

↣ histamine levels

↣ DAO activity

↣ gut barrier integrity (zonulin)

You’ll complete the at-home blood spot test, and I’ll connect your results with your symptoms to give you a clear, personalized breakdown and next steps.

Not even sure if histamine is an issue? If you've been chasing symptoms that don't have a clear explanation, histamine reactivity is worth ruling out. The quiz takes about two minutes and tells you whether it's likely part of your picture. Take the quiz →

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Disclaimer: I do not diagnose, treat, prevent, or cure any disease or condition. Nothing I share with my clients is intended to substitute for the advice, treatment or diagnosis of a qualified licensed physician. I may not make any medical diagnoses or claim, nor substitute for your personal physician’s care. It is my role to partner with you to provide ongoing support and accountability in an opt-in model of self-care and any changes should be done under the supervision of a licensed physician.