What Exactly Are Tannins In Tea? Here's Everything You Need To Know

If you could drink only one thing for the rest of your life, what would it be? William Cole, IFMCP, DNM, D.C., leading functional medicine expert, says that his top choice would undoubtedly be tea. That's because all teas have antioxidant, antibacterial, anti-inflammatory, and antiviral properties, along with their own individual benefits, depending on what's in the tea. 

But tea also contains compounds called tannins—and there's a lot of confusion about what that means for you and your health. You may have heard that tannins in tea are good for you, or you may have been told that it's a better idea to stay away from them. So, what's the deal?

The short answer is: The tannins in teas have tons of health benefits, but there are some drawbacks, too.

Tannins are plant compounds that are classified as polyphenols (or more specifically, phenolics or phenolic compounds). They naturally have a bitter, astringent taste, and there's a reason for that. 

Because tannins are unpleasant, in theory, they're produced as a defense mechanism to make the plant less palatable to keep the animal (or human) away. But when it comes to the tannins in tea, many people actually enjoy that characteristic taste. That's probably why tea is one of the most common beverages in the world, second only to water.

Tea is one of the richest sources of tannins. You know that bitter taste and dry feeling you get after taking a sip of tea? That's due to the high concentrations of tannins in the tea leaves. In fact, a report that was published in the Research Journal of Recent Sciences in 2012 points out that most of the active compounds in black tea are tannins.

But black tea isn't the only type of tea that contains tannins. All tea contains tannins, and different types of tea have varying levels. According to a January 2015 report in the Journal of Chemical and Pharmaceutical Research, black tea has the highest concentration, followed by oolong tea and then green tea. White tea, which is made from young tea leaves and is the least processed, has the lowest levels. 

Other sources of tannins include:

Like all phytochemicals, the tannins in tea have a number of health benefits that range from combating inflammation to reducing your risk of heart disease:

One of the most well-known benefits of tannins is that they act like antioxidants, scavenging and neutralizing free radicals and combating oxidative stress. Their antioxidant activity is the reason for many of the health benefits of tannins, including protection against heart disease, cancer, and allergies, according to an April 2015 report in the International Journal of Pharma Research & Review.

Because of their antioxidant properties, tannins (like all phytochemicals) also help combat inflammation. Cole explains that polyphenols, specifically, have been shown to lower TNF-a, an inflammatory cytokine that also increases C-reactive protein (CRP), a protein that rises in response to chronic inflammation. 

In a 2018 review published in Current Medicinal Chemistry1, researchers wrote that another reason tannins are anti-inflammatory is that they can help balance the bacteria in your gut, shutting off inflammatory processes that come from your gastrointestinal tract.

Tannins have strong antibacterial effects, fighting off a number of pathogens that commonly plague the human digestive system. According to a September 2009 report in Molecular Nutrition & Food Research, ellagitannins stop the growth of Staphylococcus bacteria, Candida albicans, and Campylobacter jejuni, and other tannins in tea have shown antibacterial activity against Helicobacter pylori, one of the most common causes of stomach ulcers (that can eventually lead to stomach cancer).

When combined with antibiotics, tannins also fight off antibiotic-resistant bacteria, like methicillin-resistant Staphylococcus aureus (MRSA), according to a 2015 report in Natural Product Communications2.

What's even more interesting is that in lab tests, tannins were found to be resistant to acid treatment, meaning that they can still work effectively in the harsh acidic environment of your stomach.

Tannins protect your heart in several ways: They keep heart tissue healthy2, prevent elastin (one of the major components of your blood vessels) from breaking down, and prevent the buildup of calcium on the artery walls. They also help relax your blood vessels and help your blood clot normally.

In animal studies, tannins have been shown to help lower blood glucose levels2 while simultaneously increasing insulin levels. According to a 2018 review that was published in Phytomedicine3, tannins—specifically gallic acid, ellagic acid, catechin, epicatechin, and procyanidins—can also slow the progression of diabetes and related complications, like nerve damage, kidney damage, and heart and eye problems.

Specific types of tannins, like ellagitannins and ellagic acid, have been shown to protect against the development of cancer and suppress tumor formation. According to a May 2016 report in Toxins4, part of the reason tannins help prevent cancer and tumors is that they reduce inflammation, which has been shown to be a major factor in the development of cancer. 

Another tannin, called tannic acid, is resistant to medications and positively affects the immune system, so it also shows promise as an adjuvant therapy for cancer, according to an April 2020 review in Current Pharmacology Reports.

Tannins have been shown to slow the progression of neurodegenerative disorders like Parkinson's disease and Alzheimer's disease. One big reason is that they reduce inflammation and combat oxidative stress, two causative factors for these brain disorders, but they also help reduce brain lesions, according to a June 2019 report in Molecules5.

Because of their neuroprotective effect, tannins have also been classified as a strong antidepressant, helping boost mood and overall well-being.

But when it comes to tannins, it's not all good news. Tannins also act as anti-nutrients, meaning that they block and interfere with the absorption of certain nutrients. In this case, a big one is iron.

That's why, if you're iron deficient, your doctor may have advised that you either don't drink tea or only drink it in between meals rather than with an iron-rich meal. You can also reduce any potential negative effects by adding milk to your tea. The tannins bind with the milk protein, instead of the proteins in your gut, which prevents them from interfering with iron absorption. Eating vitamin-C-rich foods, like bell peppers, potatoes, cantaloupe, and/or oranges right before or after you drink your tea can also neutralize the tannins.

According to a July 2014 report in the International Journal of Nutrition and Food Sciences, tannins can also block the digestion and absorption of proteins by either inhibiting the enzymes that you need to break them down or by making the protein biologically unavailable. 

And since tannins interfere with the proper functioning of enzymes, it can mess with your digestion as a whole. On that note, Nour Zibdeh, M.S., RDN, a functional and integrative dietitian and nutritionist, also points out that if you have a sensitivity to tannins, they can constipate you. Overconsumption of tannins can also cause stomach upset and nausea. 

However, researchers from a January 2017 study that was published in Current Developments in Nutrition6 wanted to make it clear that most studies that demonstrate a negative effect of tannins, especially when it comes to iron absorption, use amounts that you wouldn't take in with average tea consumption.

For example, one 5-ounce cup of tea typically contains around 25 to 80 mg of tannins. That means, even if you drank three cups of tea per day, you would be taking in only 75 to 240 mg of tannins. Most studies exceeded this amount, some using up to 1,000-mg doses of tannins.

Tea has so many health benefits, from the tannins and beyond, that outweigh the potential downsides. And when it comes to how tannins affect your health, the dose really makes the poison, as they say. In other words, the amount of tannins you consume in a day is a determining factor in whether they act as antioxidants or anti-nutrients in your body. If you're concerned, make sure you're limiting yourself to a cup or two a day and sticking to green and white teas only.