A large group of more than 500 different natural phytochemicals that serve as micronutrients in plants are known as polyphenols. They provide protection from multiple threats and are also responsible for the color of plants. Humans can get the benefits of polyphenols by consuming plants in their diet.

Some scientists claim that polyphenols found in plants provide major health benefits, due to their strong antioxidant action. Of all polyphenols, flavonoids have been the best researched, even if they are a massive sub-group of thousands of compounds. Almost any food supplies a mixture of flavonoids, which have various effects on human health and metabolism. Eating fruits and vegetables is the easiest way to include polyphenols in your regular diet.

Tannins, which are found as either condensed tannins or hydrolyzable tannins, and lignins are the two other major classes of polyphenols, besides flavonoids. Every plant has at least several polyphenols in its composition. Tannins for example are found in large amounts in wine, as well as in fruits and black tea.

Polyphenols are very effective antioxidants, with the ability to neutralize free radicals in the body and prevent the diseases caused by them. Free radicals are blamed for a large number of conditions, from premature aging to some types of cancer. Tannins and other polyphenols can also kill pathogens when they come in direct contact with them.

Tannins have strong effects, which can be easily noticed. The name of this group of chemicals actually comes from one of these effects: when applied on leather tannins change its color to a tan, or brown one. Besides plants, tannic acid is naturally found in the water of some lakes and rivers, especially where cypress trees grow in tropical parts of the world. While related to the polyphenol tannins, tannic acid is actually a different compound. In some cases, this chemical can be toxic to the human body.

Polyphenols have well known health benefits but the mechanisms behind them are poorly understood and scientists are not sure how these work. Some polyphenols don’t provide any health benefits and can actually damage the body in various ways. Many compounds from the tannins group are known to be toxic. Many other polyphenols have an uncertain status, since their effects are poorly researched and more studies are needed to establish their impact on human health.

Modern medicine generally considers polyphenols to be benefice but there is no consensus about what the actual benefits are, due to a lack of clinical trials. Polyphenol antioxidants usually get the credit for the health effects of wine, tea, vegetables or fruits. Even if the mechanism is not known, diets rich in fruits, vegetables and natural beverages are universally recommended.

Types of polyphenols

Polyphenols have been included by chemists in a single group because they share a specific structure that resembles a ring. They can have multiple rings and various special molecules that attach to them. Based on the chemical structure, polyphenols are divided into four different categories: flavonoids, phenolic acids, stilbenes, and lignans.

Some of the most common polyphenols are phenolic acids. They are found in many fruits and vegetables, as well as some cereals. The foods richest in phenolic acids are tea, coffee, red wine, cherries, grapes, kiwi fruits, plums or apples.

A regular diet can provide large amounts of phenolic acids, which are quite abundant. Most natural foods will provide a good supply and they are quickly digested, being absorbed through the intestinal walls. Phenolic acids provide useful antioxidant effects but some of them can also reduce inflammation.

Another type of flavonoids with both antioxidant and anti-inflammatory properties are flavonoids. This is actually a generic term for a large number of compounds that include several distinct sub-groups: isoflavones, flavones, flavonols, flavanones, catechins, anthocyanidins and chalcones.

Flavonoids are also known under the alternative name bioflavonoids. They are found in most foods with a vegetal origin, especially red wine, green tea and most legumes, fruits and vegetables. Even if they are widespread in a normal diet, they can be taken as supplements as well.

A small group of plant polyphenols are known as stilbenes. The most famous chemical of this group is resveratrol, which is a component of red wine but also found in a few other foods like cranberries, blueberries and peanuts. Its action is said to explain the benefits of these products on heart health.

The actual properties of resveratrol have never been proven and it's unknown if it actually provides these benefits. No conclusive trials on humans have been done so far but tests on lab animals have shown that it works as an antioxidant and anti-inflammatory agent, when the dosage is high enough.

Another group of polyphenols, known as lignans, are found in the highest concentrations in the seeds of flax or sesame but can also be sourced from legumes, vegetables, cereals, grains, fruits and algae.

The effect of lignans on human health have not been well researched either. A diet rich in these compounds does appear to improve the condition of the cardiovascular system. High amounts of lignans can't be supplied by a normal diet and require either consuming flax seeds or nutritional supplements.

Health benefits

Polyphenols are known for their strong antioxidant effect and the ability to prevent diseases by destroying the free radicals that can harm tissues. Free radicals are a natural by-product of the metabolism but they can accumulate in large amounts due to poor diets, stress or pollution. Unless they are neutralized, these chemicals can damage and mutate cells.

While the benefits of antioxidants remain quite controversial, studies have proven they can reduce the risk of many serious diseases, including diabetes and cancer. Polyphenols are effective antioxidants, so ingesting a larger amount as part of your diet can counter oxidative stress and reduce the risk of some serious conditions.

A diet rich in polyphenols might also decrease the risk of several heart issues. Heart diseases are caused by many possible factors however, so a healthy diet is not enough to prevent them. In the modern world, cardiovascular conditions are among the most common causes of death.

Polyphenols have been investigated by scientists as a potential natural treatment against heart diseases of all types. The American Journal of Clinical Nutrition has published the results of a study on humans focused on consuming flavonoids, which are one of the main polyphenol groups. The study revealed that people with a high intake of flavonoids have a 18 percent lower risk of death compared to the people who consumed the lowest amounts. Polyphenols can neutralize free radicals and reduce chronic inflammation, which might explain their benefits on heart diseases.

Inflammation is a natural defensive mechanism of the human body. Even in its acute form, it can protect from infections and some types of injury. However, long periods of chronic inflammation can have devastating effects. It can lead to cancer, diabetes, cardiovascular dysfunction and other lethal conditions. Eventually, the immune system can start attacking its own healthy cells.

Inflammation is reduced by polyphenols because they reduce the oxidative stress that causes it. This anti-inflammatory effect can be very useful against many diseases that share this symptom, such as inflammatory bowel disease, rheumatoid arthritis or lupus. Polyphenols can also make the body healthier by preventing diseases in general.

With aging, blood clots can become a serious health risk for many people. The platelets that are a normal component of human blood can start to bind together, a process known as platelet aggregation, forming dangerous blood clots. This is actually a normal mechanism designed to close wounds and prevent bleeding. However, it can also lead to serious diseases like pulmonary embolism, deep vein thrombosis and especially strokes.

Polyphenols are some of the natural compounds currently investigated for preventing platelet aggregation. Many recent studies have focused on resveratrol, a polyphenol found in the composition of red wine, as well as the skin of some berries. It has been tested in vitro and on animals, with the results proving that it can indeed reduce the risk of blood clots by interfering with platelet aggregation.

Polyphenols are mainly known for their benefits on cardiovascular health but scientists have recently started to consider them as potential weapons against cancer, since they can inhibit the growth of tumors. In vitro studies have proven that the growth of cancer cells can be reduced by several types of polyphenols, especially flavanols, flavanones, phenolic acids and anthoncyanins.

Most of the foods that are known to help in the fight against cancer are rich in both antioxidants and polyphenols. This is further evidence that they are good for human health and should be included in your diet. The best sources of polyphenols are leafy green vegetables, fresh herbs and spices, forest berries and fruits from the citrus family.

When the level of glucose in the blood becomes too high, the initial symptoms are weight loss, general fatigue and frequent urination. If blood sugar is not controlled, it can cause more serious health problems on the long term. The most common is diabetes, which in turn leads to poor vision, damaged nerves or slow wound recovery.

Blood glucose levels can be balanced in a natural way with the help of some polyphenols. Multiple in vitro studies completed in Australia in 2016 have found that an increased intake of polyphenols can reduce dangerous spikes of blood sugar levels. This is achieved by an increased insulin secretion, as well as the inhibition of some enzymes that transform dietary starches into glucose. The British Journal of Nutrition has also published a recent study that associates a reduced risk of type 2 diabetes with a diet rich in polyphenols.


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