Polyphenols – Lifespan Essentials

By Dr Harold Gunatillake
Health Writer

Polyphenols have recently been termed “lifespan essentials”, and they actively participate in the body to prevent diseases from occurring. Polyphenols are antioxidants from plant foods that work in the body to enhance health in complex ways, and as such they are not simply antioxidants. Their specific health-promoting actions are still being actively researched, and it is generally recognized that they can reduce the risk factors for cardiovascular disease and basically help to protect many body systems from the risks or ravages of many types of chronic disease. Boosting one’s intake of antioxidant polyphenols on a daily basis is easy to do, and can be a tasty, gourmet adventure.

They are also antioxidant micronutrients containing a poly-phenolic or natural substructure.

There are over 4000 of them and most of them have antioxidant activity in vitreo, meaning studies in the laboratory. They also have the function of signaling from cell to cell, receptor sensitivity and gene regulation.

These polyphenols found in plants are natural metabolites that have antioxidant properties in humans as mentioned before. The U.S. Department of Agriculture has not yet established a recommended daily intake for polyphenols or calculated current average polyphenol consumption in America. Polyphenols are categorized as phenolic acids, flavonoids or tannins, all of which are antioxidants. Only eating a variety of food sources of polyphenol provides access to all three types.

Polyphenols are abundant micronutrients in our diet, and their role in preventing degenerative diseases, including cancer has come to light in recent studies, and their role in the prevention of various diseases associated with oxidative stress, such as cancer, cardio-vascular disease and neurodegenerative diseases. In addition being functioning as antioxidants these polyphenols have other functions found in medicinal plants, modulate the activity of a wide range of enzymes and cell receptors in this way.

In human usage of these polyphenols they may not be absorbed with equal efficacy. They are extensively metabolized by intestinal and hepatic enzymes and by the intestinal micro flora. Knowledge of the bioavailability and metabolism of the various polyphenols is necessary to evaluate their biological activity within target tissues.

There are several thousands of phenol molecules having phenolic structure, (i.e., several hydroxyl groups on aromatic rings) have been identified in higher plants, and several hundred are found in edible plants. These molecules are secondary metabolites of plants and are generally involved in defense against ultraviolet radiation or aggression by pathogens.

These polyphenols are flavonoids, stilbenes, isoflavones, proanthocynadins, catechins and anthocyanidins.

Flavonoids: and flavonols

Flavonols are the most ubiquitous flavonoids in foods, and the main representatives are quercetin and kaempferol. They are generally present at relatively low concentrations of ?15–30 mg/kg fresh wt. The richest sources are onions (up to 1.2 g/kg fresh wt), curly kale, leeks, broccoli, and blueberries. Red wine and tea also contain up to 45 mg flavonols/L. These compounds are present in glycosylated forms.

Flavones are much less common than flavonols in fruit and vegetables. Flavones consist chiefly of glycosides of luteolin and apigenin. The only important edible sources of flavones identified to date are parsley and celery. Cereals such as millet and wheat contain C-glycosides of flavones. The skin of citrus fruit contains large quantities of polymethoxylated flavones: tangeretin, nobiletin, and sinensetin (up to 6.5 g/L of essential oil of mandarin). These polymethoxylated flavones are the most hydrophobic flavonoids.

In human foods, flavanones are found in tomatoes and certain aromatic plants such as mint, but they are present in high concentrations only in citrus fruit. The main aglycones are naringenin in grapefruit, hesperetin in oranges, and eriodictyol in lemons. Flavanones are generally glycosylated by a disaccharide at position 7: either a neohesperidose, which imparts a bitter taste (such as to naringin in grapefruit), or a rutinose, which is flavorless. Orange juice contains between 200 and 600 mg hesperidin/L and 15–85 mg narirutin/L, and a single glass of orange juice may contain between 40 and 140 mg flavanone glycosides

Lignans

The richest dietary sources of this polyphenol is linseed. which contains secoisolariciresinol (up to 3.7 g/kg dry wt) and low quantities of matairesinol. Other cereals, grains, fruit, and certain vegetables also contain traces of these same lignans, but concentrations in linseed are ?1000 times as high as concentrations in these other food sources. Lignans are metabolized to enterodiol and enterolactone by the intestinal micro flora.

Stilbenes

Stilbenes are found in only low quantities in the human diet. One of these, resveratrol, for which anticarcinogenic effects have been shown during screening of medicinal plants and which has been extensively studied, is found in low quantities in wine (0.3–7 mg aglycones/L and 15 mg glycosides/L in red wine) However, because resveratrol is found in such small quantities in the diet, any protective effect of this molecule is unlikely at normal nutritional intakes.

Fruits:

Fruits are a good source of polyphenols, further classified as flavonoids and tannins. Dark red fruits seem to have more polyphenols, particularly dark plums, cherries and berries.

Strawberries, blueberries and raspberries are a good source of ellagic acid, tannin. Apples, grapes, pears, cantaloupe and cranberries are also good sources of polyphenol antioxidants.

Vegetables:

Veggies have a lower concentration of polyphenols than fruits. Onion, broccoli, cabbage, celery, and parsley are reliable sources of flavones and flavonols, types of flavonoids. Red-tinted vegetables like beets, cabbage and rhubarb are highest among vegetables in overall polyphenol content.

Grains and Legumes:

Both grains and legumes are good sources of polyphenols. Most legumes, including beans, peas and nuts, contain flavonoids. Soybeans are a common source of isoflavones, another type of flavonoids. Whole grain foods, oats and rye also contain polyphenols, particularly phenolic acids.

Chocolate and Coffee:

These also have been found to have phenolic acids, a type of polyphenol. In fact, after grain products, coffee is believed to be the greatest source of polyphenols in the American diet. Coffee and cacao are rich in caffeic acid and ferulic acid, two polyphenol antioxidants. The polyphenol content in chocolate is directly related to its cacao content, with dark chocolate having much more than milk chocolate.

Red Wine:

Another favorite source of polyphenol antioxidants is red wine. White wine does not sit on the skins of the grapes and therefore does not receive nearly as much of the phytonutrients as occur in red wine. Of course, all alcohol products have to be consumed in moderation. Nevertheless, the tannins and flavonoids available in red wine are believed to explain why the French have low incidence of heart disease despite a diet high in saturated fat.

The many analytic studies of polyphenols in foods that have been conducted to date provide a good indication of polyphenol distribution. Fruit and beverages such as tea, red wine, and coffee constitute the principal sources of polyphenols, but vegetables, leguminous plants, and cereals are also good sources. Polyphenol concentrations in foods vary according to numerous genetic, environmental, and technologic factors, some of which may be controlled to optimize the polyphenol content of foods. The main tasks ahead are identifying the plant varieties that are the richest in the polyphenols of interest, improving growing methods, and limiting losses during the course of industrial processing and domestic cooking.