What are DAO enzymes?

Educational information only: This article is provided for general educational purposes and has not been evaluated by the Food and Drug Administration. It is not medical advice and is not intended to diagnose, treat, cure, or prevent any disease. Please talk with a qualified healthcare provider about your individual health needs before starting any supplement or changing your diet or medication.

DAO is a digestive enzyme, found mainly in the lining of the small intestine and in the kidneys, that uses copper to help break down the histamine naturally present in food.¹ That's dietary histamine — different from the histamine your immune system releases during a true allergic reaction. For most people this process runs quietly in the background. For others, it doesn't keep pace, and dietary histamine can build up enough to be noticeable.

Below, we're answering the questions we hear most often about DAO enzymes — from the nutrients that support them, to the vitamins tied to histamine balance, to what is most important when looking for a DAO enzyme supplement.

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What depletes the DAO enzyme?

A handful of factors are consistently linked to lower DAO activity:

• Alcohol — especially wine and beer, among the most consistently cited DAO blockers
• Black tea and mate tea
• Energy drinks
• Certain medications — some antihistamines, mucolytics, antiemetics, and NSAIDs have been associated with reduced DAO activity in various studies¹

Eating a large amount of high-histamine food in one sitting can also outpace whatever DAO activity is available, even when DAO itself isn't technically "depleted." If you take a prescription medication and are concerned it may affect your DAO activity, ask your healthcare provider or pharmacist rather than stopping or changing a medication on your own.

How can I increase my DAO enzyme naturally?

Genetics and diet both play a role in DAO activity, which is part of why responses vary so much from person to person.¹³ What you can do is make sure your body has the nutrients DAO relies on to function well, and avoid the habits most likely to work against it.

Nutrients tied to DAO function

• Copper, zinc, and iron — found in whole grains, sweet potatoes, chicken, and potatoes
• Vitamin B6 — found in oats, tuna, and rice
• Vitamin C — found in bell peppers, broccoli, and Brussels sprouts
• Phosphorus and magnesium — found in turkey, eggs, and dark leafy greens

Habits worth limiting

It's just as important to avoid working against your own DAO activity — see "What depletes the DAO enzyme?" above for the main culprits. Green tea is generally considered the exception among teas, since it doesn't carry the same association as black or mate tea.

Because diet alone can't guarantee your DAO activity is where you'd like it, many people pair these habits with a daily DAO enzyme supplement to help support the breakdown of dietary histamine before meals.*

How do I know if I need a DAO enzyme?

There's no simple at-home test for DAO activity — it's genuinely difficult to measure, even in a lab setting.¹ Instead, most people start paying attention to patterns: noticing that certain higher-histamine foods — aged cheese, cured meats, wine, fermented foods, leftovers — seem to bring on the same cluster of reactions again and again, especially when eaten in larger amounts or close together.

It's worth noting that this cluster of reactions, often called histamine intolerance, isn't currently recognized as a distinct medical condition by the American Academy of Allergy, Asthma, and Immunology, and researchers are still working out exactly what causes it in different people.¹ If you notice a recurring pattern, it's worth bringing it up with a healthcare provider rather than self-diagnosing — they can help rule out other causes and talk through whether a DAO enzyme supplement, taken before meals, makes sense to try alongside dietary changes.*

One small pilot study followed 28 people with HIT who took DAO capsules before meals for four weeks: symptoms across 22 tracked measures improved significantly during supplementation, then increased again once participants stopped.² It's a promising early signal, though worth reading with its limits in mind — the study was open-label with no placebo group, so it doesn't confirm cause-and-effect on its own.*

What is the best DAO enzyme supplement?

Not all DAO supplements are built the same way. A few things worth comparing:

• Potency — measured in HDU (HDU is how DAO activity is standardized across products)
• Source — porcine-derived DAO is the form used in the published human clinical research, while pea-derived DAO is more common in plant-based formulas but has less human data behind it
• Release format — a delayed-release capsule is designed to reach the small intestine, where DAO does its work, rather than breaking down too early
• Testing and manufacturing — third-party testing and GMP-registered facilities

OmneDiem's DAO enzyme line was built around this exact checklist: porcine-derived DAOgest® (the clinically studied form), delayed-release capsules, GMP-registered manufacturing, and a choice of three potency tiers so you can match the dose to your needs.*

Third-party review

Independent review site Innerbody named OmneDiem's Histamine Digest PureMAX its “Best High-Dose” pick in its roundup of DAO supplements for histamine intolerance, pointing to its 40,000 HDU per capsule — the highest DAO activity among the supplements it reviewed.

Read the full review on Innerbody

OmneDiem has been a pioneer in DAO enzyme supplementation, and its line is built around DAOgest® — developed in partnership with Bioiberica, a European nutraceutical manufacturer with more than 20 years of experience producing ingredients under strict GMP standards.⁴ DAOgest is a standardized, transparently-sourced porcine-derived DAO extract — the same form of DAO used in the human clinical research on DAO supplementation²:

• Histamine Digest — 30,000 HDU per capsule, an everyday option
• Histamine Digest PureMAX — 40,000 HDU of pure DAO per capsule, for those wanting a higher-potency option
• Histamine Complete — 15,000 HDU per capsule, combined with bromelain, quercetin, vitamin C, and stinging nettle leaf for broader seasonal and dietary histamine support*

Third-party review

Independent review site Lifespan Vault called OmneDiem's Histamine Digest “the highest-potency DAO enzyme in the direct-to-consumer aisle,” rating it Premium tier at 30,000 HDU per serving. The review also notes it's best suited for people already working with a clinician on dietary histamine, rather than as a first step for self-diagnosing — guidance we'd echo as well.

Read the full review on Lifespan Vault

What are HDUs?

HDU stands for Histamine-Degrading Units — it's the standard measurement used to describe a DAO enzyme supplement's potency, similar to how CFUs are used to measure probiotic strength. The number reflects how much histamine-breakdown activity is packed into a single capsule: a 30,000 HDU capsule and a 40,000 HDU capsule both contain DAO enzyme, but the second has a higher concentration of active enzyme per serving.

HDU is one of the clearest ways to compare DAO supplements side by side, alongside the enzyme's source (porcine vs. pea, covered below) and whether the product is third-party tested.

Porcine vs Pea DAO

DAO supplements are made from one of two sources: porcine (pig) kidney or pea shoots. The two aren't interchangeable from a research standpoint. Porcine-derived DAO is the form used in the published human clinical studies on DAO supplementation, while pea-derived DAO is more commonly chosen by people following a vegetarian or vegan diet, though it has less direct human research behind it. OmneDiem's DAO enzyme line uses DAOgest®, a standardized porcine-derived DAO extract, for that reason. A recent review of DAO-rich supplements found meaningful differences between enzyme sources, reinforcing why it's worth checking where a supplement's DAO actually comes from.³

For a deeper breakdown of the two sources, see our full guide: Porcine-Derived DAO vs. Pea-Derived DAO.

Which is better, quercetin or DAO?

These two ingredients get mentioned together often, but they work at different points in the process. DAO enzyme works in the gut to help break down dietary histamine that's already present in food, before it's absorbed. Quercetin is a flavonoid antioxidant sometimes described as a mast cell stabilizer — researchers have studied whether it may help calm the release of histamine from mast cells in the first place, rather than breaking down histamine that's already there.¹

So it's less a question of which one is "better," and more a question of which stage of the process each one supports.* That's the thinking behind OmneDiem's Histamine Complete, which combines DAO enzyme with quercetin, bromelain, vitamin C, and stinging nettle leaf in one formula, for support across both mechanisms.*

What vitamin deficiency causes high histamine?

DAO doesn't work alone — it needs copper as a direct cofactor, and research has also pointed to vitamin B6 as playing a supporting role in healthy DAO activity.¹ When levels of these nutrients run low, some researchers believe it may be associated with reduced DAO function, which in turn could make it harder for the body to keep up with dietary histamine. It's an association worth knowing about, not a confirmed cause-and-effect — and it's not a substitute for having nutrient levels checked by a healthcare provider if you're concerned.

Hormones and Histamine: What's the Connection?

Histamine isn't only a dietary story. Hormones play a role too, particularly estrogen and progesterone, both of which interact with mast cells — the immune cells that release histamine. Estrogen is generally associated with increased mast cell activity and with histamine lingering longer in the body, while progesterone is thought to have more of a calming effect on mast cells.

This may be part of why some people notice histamine-related reactions shifting around hormonal changes — before a period, around ovulation, or during perimenopause, when progesterone typically declines first and estrogen fluctuates unpredictably. For those who already run sensitive to dietary histamine, this hormonal shift may add to the picture. We've written about this pattern before: see The Histamine Hormone Trend.

Reactions described as overlapping between histamine activity and perimenopause include flushing, itchy skin or hives, digestive upset, a racing heart on standing, brain fog, fatigue, mood changes, and cyclical head pressure that tracks with the menstrual cycle. It's worth saying plainly: this connection is considered biologically plausible, but it hasn't been confirmed through controlled clinical trials. It's best treated as a pattern worth raising with a healthcare provider — ideally one familiar with both hormone health and histamine — rather than a confirmed diagnosis.

What are the signs of too much histamine in your body?

After eating higher-histamine foods, people who are sensitive to dietary histamine commonly report a cluster of reactions, including:

• Flushing or facial warmth
• Itchy skin or hives
• Head pressure or a pounding, uncomfortable feeling in the head
• Nausea
• Digestive upset, including diarrhea
• A faster-than-usual heartbeat
• Nasal congestion

Which vitamin lowers histamine?

Vitamin C is the one most often discussed in connection with histamine balance. Some research suggests it may help support the body's normal handling of histamine, though the evidence so far is preliminary and mixed rather than conclusive.* Vitamin B6 is also worth keeping in adequate supply, given its supporting role in DAO activity discussed above.

As always, no single vitamin is a stand-in for a full picture of diet, nutrient status, and (when needed) guidance from a healthcare provider — but making sure you're not running low on either one is a reasonable, low-risk place to start.

Taken together, this is why OmneDiem's DAO enzyme line is worth a look if you're weighing options: a pioneer in DAO enzyme supplementation, built on DAOgest® in partnership with Bioiberica, using the same porcine-derived form studied in published human research, manufactured under GMP standards, available across three HDU tiers to match different needs, and independently recognized by both Innerbody ("Best High-Dose") and Lifespan Vault (Premium tier, highest-potency in its category).*

Ready to support your DAO levels?

Explore OmneDiem's full line of DAO enzyme supplements, including Histamine Digest, PureMAX, and Histamine Complete. Subscribe & Save ships free in the US and saves 10% on every order.

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. The information in this article is for educational purposes only and is not a substitute for professional medical advice. Talk to your healthcare provider before starting any new supplement, especially if you are pregnant, nursing, have a kidney condition, or take prescription medication.

1. WebMD, “What to Know About Diamine Oxidase and Histamine Intolerance”

2. Schnedl WJ, Schenk M, Lackner S, Enko D, Mangge H, Forster F. “Diamine oxidase supplementation improves symptoms in patients with histamine intolerance.” PMCID: PMC6859183.

3. ScienceDirect, review of diamine oxidase biology, genetic and dietary factors, and supplementation strategies in histamine intolerance.

4. Bioiberica, “DAOgest.”