One more reason to drink wine in moderation, according to research

Research shows that the occasional glass of wine has numerous health benefits. The polyphenols—resveratrol, anthocyanins, and catechins—are the highest-profile antioxidants found in wine, and are much-touted for their health effects.

According to a review published in Nutrients, resveratrol, for instance, “is active in the prevention of cardiovascular diseases by neutralizing free oxygen radicals and reactive nitrogenous radicals; it penetrates the blood-brain barrier and, thus, protects the brain and nerve cells. It also reduces platelet aggregation and so counteracts the formation of blood clots or thrombi.”

Although resveratrol garners the lion’s share of attention with respect to phytochemicals of health interest found in wine, there are other beneficial compounds of note. Tannins are non-flavonoid polyphenols that also decrease the risk for chronic disease. Researchers are just beginning to uncover the importance of tannins.

In celebration of National Wine Day—yes, it's today!—let’s take a closer look at tannins.

What are tannins?

Tannins are polyphenols that are astringent and found in different parts of herbs and plants. They are characterized as condensed (ie, non-hydrolyzable) or hydrolyzable tannins. Condensed tannins are more common in nature and are found in legumes, stems, trees, and forages. On the other hand, hydrolyzable tannins are found in fruits, bark, wood, and seedpods.

In addition to grapes, fruits that are high in tannins include berries, dates, pomegranates, apples, bananas, peaches, and plums. Along with wine, tannins are well-represented in many of the foods and beverages including tea, beer, ice cream, and chocolate. 

Health benefits of tannins

As detailed in an article published in Toxin Reviews, tannins offer multifarious health benefits. Among them, tannins:

• Decrease the risk of diabetes by increasing glucose uptake and lowering blood sugar. 

• Encourage wound healing by forming a protective covering against bacteria. Diluted solutions of tannins are used to treat skin ulcers and lesions due to sore throat.

• In condensed form can treat allergies, including allergic rhinitis, asthma, and hypersensitive pneumonitis

• Possess anti-inflammatory, antineoplastic, antiallergic, and anthelmintic properties.

• Boast antihemorrhoidal and antidiarrheal properties.

• Decrease risk of heart disease (antioxidant properties of tannins prevent cholesterol oxidation, which forms plaques in blood vessels). In their proanthocyanidin form, tannins inhibit the production of peptides that result in artery hardening.

• Possess various antiviral properties. In particular, those in red wine inactivate enteric virus, herpes simplex virus, poliovirus, and more. Tannins also battle HIV.

• Boast antimicrobial activity against H. pylori, S. aureus, C. botulinum, and more.

• Have anticarcinogenic properties, as well as antimutagenic activity versus alfatoxinB, 2-aminofluorene, and Benzo-(a)-pyrene.

In a review published in Phytochemicals, the authors stressed that the anticancer effects of tannins are well-supported in the research. Tannins facilitate various signaling pathways involved in tumorigenesis.

According to the authors, “In vivo and in vitro studies provide evidence that anti-cancer effects of various tannins are predominantly mediated through negative regulation of transcription factors, growth factors, receptor kinases, and many oncogenic molecules.”

On a related note, experts point out that tannins have low bioavailability. In order to become more bioavailable, microbiota in the gut play a crucial role, according to the authors of a review published in Microorganisms.

“Microbiota-mediated hydrolysis of tannins produces highly bioaccessible metabolites, which have been extensively studied and account for most of the health effects attributed to tannins,” the authors wrote. 

Bottom line

Although resveratrol gets most of the attention for the health benefits of wine, tannins and other non-flavonoids also contribute. The importance of tannins is emerging in the research, and perhaps provides another good reason to drink wine—in moderation, of course. And for those who don’t imbibe alcohol, tannins are also found in a variety of other foods and beverages.