Polyphenols play a big part in wine's claim to health-benefit fame. But can you actually explain why wine's polyphenols are good for you? Or even what a polyphenol is? For those without degrees in organic chemistry, understanding these compounds can seem daunting.
Let's break it down.
What is a polyphenol?
Let's start with an even more common term in the wine-health lexicon: antioxidants, molecules that protect against the harmful effects of oxidation. Not to be confused with the flaws caused by wine oxidation (which is harmless to your health), oxidation in the human body is the breakdown of oxygen molecules caused by everyday occurrences such as exercise, metabolizing food and environmental factors such as exposure to air pollutants. Those chemical reactions generate free radicals, which can lead to aging, inflammatory diseases and even cancer.
"Free radicals are uncharged molecules, which are highly reactive because they have an odd number of electrons," explains Ginger Hultin, a Seattle-based registered dietitian and spokesperson for the Academy of Nutrition and Dietetics. "They can damage the outside of cells, or cellular membranes, as well as DNA, which is why we don't want too many of them bouncing around." Luckily, antioxidants can prevent this damage by lending their own electrons to stabilize free radicals. "There are a lot of different types of free radicals, so the body needs a lot of different types of antioxidants to quench them," Hultin adds.
Polyphenols are one such subset of antioxidants. They get their name from their structure: A "phenol" is a type of chemical compound; "poly" means there is more than one of those compounds that make up the molecule. There are thousands of different types of polyphenols that exist naturally in plants; the roles polyphenols play can vary from helping create pigment to providing protection against ultraviolet rays to repairing physical damage, depending on the specific needs of each plant type.
Wine's polyphenols come from grapes, mainly from the skins, and because the red-winemaking process involves more extended contact with the grape skins, those wines tend to contain a lot more polyphenols than white wines do. As a whole, red wine's polyphenol content has been praised by wellness-conscious drinkers, but there are also specific polyphenols in red wine that have been studied individually for their potential health benefits.
One of the most widely studied polyphenols in wine, resveratrol is naturally produced in plants in response to physical harm, or invasion by pathogens. Also found in high quantities in peanuts, blueberries and cacao, resveratrol is extracted from plant sources to create cosmetic products and dietary supplements.
In lab studies, scientists have found that resveratrol offers protective effects against many human health risks. Two of its chief benefits are its potential to fight different cancers, by inhibiting cancerous cell growth, and its potential to fight cardiovascular disease, by preventing blood-vessel damage, lowering bad cholesterol and raising good cholesterol.
Researchers have also found evidence that resveratrol may help battle neurodegenerative diseases such as Alzheimer's, by helping to slow the disease's progression and clearing out harmful plaque buildup in the brain. It may also stave off type 2 diabetes, by helping regulate insulin.
However, the amount of resveratrol used to test this polyphenol's healthy properties isn't always the amount that is found in an average serving of red wine. While some studies have shown that quantities of resveratrol found in just one or a few glasses of wine can confer some health benefits, many others have shown that the amounts of resveratrol used to produce other health benefits could require a person to drink as many as hundreds of glasses per day. Of course, heavy drinking (let alone the impossible task of drinking 100 glasses of wine in one day) is associated with negative health benefits, so consuming lots of wine just to get reap its resveratrol-related benefits is inadvisable.
For now, many scientists remain skeptical that humans could benefit from resveratrol just from moderately drinking wine; others believe that a glass of wine's resveratrol content still might lend a health boost.
If you know resveratrol, you may have also heard of quercetin. One of the most abundant polyphenols found in food sources, quercetin has significant anti-inflammatory properties that have been studied for their ability to alleviate lung disease and promote healing in arteries.
It also has antiviral properties, and is believed to reduce the risk of contracting the flu. Like resveratrol, it has also been studied for its potential to become a chemoprotective or chemotherapeutic agent for certain types of cancer.
Anthocyanins are pigments that can create red, purple or blue colors in plants and foods and beverages made from them, including red wine. Due to different chemical processes, these polyphenols can take different forms, many of which have been studied for their human health effects, including killing leukemia cells in lab tests, as well as helping with weight maintenance and erectile dysfunction.
Procyanidins are a subgroup of condensed tannins, and in red wine are found in higher concentrations than other commonly studied polyphenols like resveratrol. Research has shown that procyanidins are particularly beneficial for their ability to moderate production of endothelin-1, a peptide that in excessive amounts has been linked to heart disease.
In plants, ellagic acid serves many functions, from regulating plant growth to protecting against infections. Though this polyphenol hasn't received quite as much attention from health researchers, studies have found it could potentially play a key role in fat-burning and liver health, even in doses as small as those found in a few servings of wine. A few years ago, a series of studies found that ellagic acid could regulate blood glucose levels in mice, as well as burn fat in fatty liver tissues in lab tests.
Commonly touted as a healthy component in tea, catechins are also found in red wine (white wine too, at much lower quantities), as well as fresh fruits, cacao and beer. They are one of the few categories of polyphenols, alongside procyanidins and ellagic acid, that have been shown to have beneficial health effects in low doses.
Past studies have looked at catechins' abilities to delay tumor development, likely by helping form another polyphenol, acutissimin A, a potential anti-cancer treatment. Catechins have also shown promise as treatments for Alzheimer's.
Do certain red wines have more polyphenols than others?
We already know that red wines have far more polyphenols than white wines, but even among the former category, certain grapes have been proven to contain higher levels of some types of polyphenols than others, and therefore wines made with these grapes are also likely to have higher levels. Wines that are dark in color and high in tannins have been shown to naturally have higher-than-average polyphenol content. Specifically, wines with lots of procyanidins are made from tannic grapes including Tannat (prominent in Uruguay), Sagrantino (indigenous to Umbria), Petite Sirah, Marselan (a French cross between Cabernet Sauvignon and Grenache), Nebbiolo and Oseleta (a Veronese blending variety). Also, though many believe that resveratrol is found most commonly in thick-skinned grapes such as Cabernet Sauvignon, studies have shown that Pinot Noir, a very thin-skinned grape, has high levels of this polyphenol, too.
But while a wine’s polyphenol content may depend a lot on a grape’s genetics, it also has to do with where the grape is grown, and how the wine is made. Past studies comparing the polyphenol content of the same grape varieties grown in different regions displayed notably different results—largely because different climates and growing conditions affect the quantities of polyphenols that a plant needs to produce. The timing of when the grapes are picked can also play a role, as polyphenol levels vary depending on ripeness.
Then there are the factors during the winemaking process. In 2016, a study published in the research journal Materials showed that fermentation positively affected a wine's total polyphenol count, while adding sulfur dioxide negatively affected it.
Further, studies have shown that aging tends to lower polyphenol count, so younger wines will likely have more polyphenols than older ones.
The sum is more than its parts
Though there has been a lot more scientific interest in wine's health benefits in the last couple decades, we are still a long way from knowing how each of these polyphenols uniquely affects our health. For starters, there are so many different types of them in a single glass of wine—or cup of tea, or serving of fruit—that singling out the functions of just one of these compounds in the human body (plus all the other health and lifestyle factors that differ from person to person) is virtually impossible.
In fact, many experts believe that we shouldn't focus on the potential of individual polyphenols, but rather on what happens when they're consumed together. "Because there is still so much to learn about [polyphenols], I wouldn't suggest focusing on just one, [but] rather on a variety that we get from eating whole foods in our diet," Hultin says.
A big part of learning more about polyphenols is understanding how they are metabolized and then put to work in the human body. Bioavailability is a key issue when humans consume polyphenols. "When you consume a chemical compound in a food matrix, there is a long way from your mouth to a target tissue [such as the heart or liver]," explains Dr. Cesar Fraga, a researcher at U.C. Davis' nutrition department. "The compound—if any—that reaches a target tissue can be chemically different from what you consume."
Though wine-derived polyphenols are certainly healthy, they're not quite on the same level as other nutrients; there are no official recommendations for daily dietary consumption of polyphenols.
"There are efforts to determine daily recommendations for certain polyphenols," Fraga said. "The road for such determination [includes] observational studies, epidemiological data, clinical data, biochemical mechanistic data. Collecting all these data takes time and coordinated efforts; it has not been done with wine."
Hultin concurs. "Polyphenols and other antioxidants are more complicated than vitamins and minerals, which are considered 'essential nutrients,'" she said. "For example, we know how much calcium is needed to support bone health based on large, long-term population studies. With vitamins and minerals, deficiency has clear and severe health consequences. Is resveratrol potentially beneficial to health? Quite possibly! Will you die if you don't get enough? Likely not … but it's yet unclear."
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