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The Truth about Antioxidant & Free Radicals

Antioxidants work in the body by neutralizing and eliminating free radicals.

The dictionary defines antioxidants in a very clear way:

an·ti·ox·i·dant

–noun

Biochemistry: an enzyme or other organic substance, as vitamin E or beta carotene, that is capable of counteracting the damaging effects of oxidation in animal tissues.

According to US Department of Health and Human Services / National Institute of Health, National Center for Complementary and Alternative Medicine, There is limited scientific evidence to support the use of antioxidant supplements to prevent disease. Observational studies (which track a group of people without changing their activities or providing special treatments) have shown that a higher intake of antioxidant-rich vegetables and fruits is associated with a reduced risk of certain chronic diseases. It is not clear, however, that the benefits are due to the antioxidants.

Reminders:

Do not use antioxidant supplements as a replacement for a healthful diet or conventional medical care, or as a reason to postpone seeing a doctor about a medical problem.

In the early 1990's, antioxidants began to gain attention and momentum when scientists realized that cancer, vision loss, clogged arteries and many other conditions were related to the damage caused by "free radicals". Early studies showed that people who did not consume enough fruits and vegetables were at greater risk of atherosclerosis, diabetes and other diseases. Those who ate plenty of fresh fruits and vegetables, rich in antioxidants, appeared to avoid these chronic and sometimes life-threatening conditions. Researchers are continuing to find that many diseases are prevented or improved with the help of antioxidants, either from a healthful of diet or from supplements.

There are many products now that claim that they are antioxidants. They claimed that they are the best among others. Others claimed that they are very effective for different disease, very effective in treating cancer. They use tri-media to promote its health benefits and to expand their business. Those claims or hype usually are based on personal testimony or experiences in using such products. These claims are exciting, but it’s important to note that these products do nothing in terms of prevention unless combined with a healthy lifestyle.

Claims regarding specific health issues are strictly regulated by local and foreign health institution of the government like the FDA of America and our own FDA Philippines formerly known as BFAD.

The Hype:

Antioxidants are a “magic pill” that will cure and prevent illness, disease and aging. When the initial research showed promising results, many people latched on to antioxidants, hoping they would be the cure for everything from wrinkles to cancer. They also hoped that antioxidants would slow the aging process, allowing lifespans of a hundred years or more.

Many of these products were carried by networking companies who made the hype for antioxidants but focused merely in the networking and earning potentials and not on the benefits of the products they are selling.

The Hope:

International case studies have offered encouraging results. Antioxidants appear to play a major role in preventing many conditions commonly associated with aging such as Alzheimer's, cancer, atherosclerosis, macular degeneration and many more. They also appear to boost the immune system, prevent cancer and relieve the symptoms of diabetes and other chronic conditions. Antioxidants contain the hope of a longer life expectancy and a greater quality of life. For example, mice engineered to produce high levels of an antioxidant enzyme live 20% longer and had less heart and other age-related diseases. Studies are underway to see if those results translate to similar results in humans. If this is true, people could live beyond 100 years and enjoy a healthier life.

What to believe?

Recent studies have shown that antioxidants are effective in boosting the immune system, preventing and treating cancer, Alzheimer's, and many other chronic conditions. Studies have also shown a difference between natural antioxidants found in fruits and vegetables and synthetic antioxidants found in laboratories and manufactured supplements. The results presented support the belief that antioxidants are essential for good health and when consumed in the right amounts and combinations can greatly enhance the quality of healthy living.

Antioxidants

Antioxidants are chemical and or natural compounds that can bind to free oxygen radicals preventing these radicals from damaging healthy cells.

The use of antioxidants supplements has become very popular in our country with influence from tri media and our quest for healthier life. Researchers are continuing to find that many diseases are prevented or improved with the help of antioxidants, either form a healthful diet or from taking antioxidant supplements.

Glutathione, lipoic acid, and CoQ10 are antioxidants formed naturally by the body but their levels decline with age, and further affected if your taking any medications for high blood pressure and diabetes. Vitamins C and E are necessary anti-oxidants but not produced by the body and must be obtained from the diet by taking citrus and other vitamin C rich foods like green pepper.

The most common antioxidants are the vitamins A, C, and E. Additional antioxidants are natrol, found in grapes and wine; selenium; and melatonin that also effective to induce sleep. Flavonoids consist of a large family of antioxidant compounds found in fruits and vegetables that helps to absorb vitamin C and other nutrients important to our immune system. Among the well-studied flavonoids in terms of cancer prevention are catechins from green tea,

genistein from soy, curcumin from turmeric, anthocyanosides from blueberries, and quercetin from yellow vegetables. More recent studies have added acai berry to the list of foods high in antioxidants and essential fatty acids.

The Process of Oxidation

Take a look at antioxidants in action. When you cut open an apple, the flesh of the apple will become brown rather quickly due to the oxidation process and free radical formation. Rub lemon juice (which contains vitamin C - a powerful antioxidant) on the apple, it won't brown as quickly. That's what happens in your body, on a cellular level, when you consume antioxidants to protect yourself from free radical damage.

Free radicals are naturally produced in the body through the normal metabolism of amino acids and fats. These free radicals are unstable molecules that can freely react with and destroy healthy cells. They can bind to and alter the structure of DNA thus leading to mutations and eventually to cancer. Besides cancer, this oxidative stress on the cells can lead to heart, eye, and neurological diseases.

Sources of Free Radicals

Free radicals are produced in the energy production within our cells. Normally, free radicals are produced in the abnormal oxidation and breakdown of fats or the poly unsaturated fatty acid, from the breakdown of hydrogen peroxide and from normal metabolism. These free radicals can damage proteins, fats and nucleic acids or our DNA and RNA and could lead to more serious problems in our body.

There are a number of known free radicals that occur in our body, such as superoxide radicals and hydroxyl radicals, hypochlorite radicals, hydrogen peroxide, various lipid peroxidases and nitric oxides. These are oxygen derive free radicals that are produce by our exposure to various agents and in the normal metabolic processes in our body.

There are pro-oxidants in our digestive tract that leads to production of more free radicals this includes:

  • traces of heavy metals – lead, cadmium, mercury, arsenic and possibly other toxic substances like pesticide residues, fungicides, herbicides, etc that even at acceptable levels, they are still able to participate in lipid peroxidation

  • Peroxidized poly unsaturated fatty acids (PUPAs), present in most fried foods in various concentrations. If cooked meat is stored, the level of PUPAs increases dramatically

  • Copper and iron ions that can be freed during digestion from various food products, especially if iron fortified food is consumed

  • Haem, a part of meat foods,

  • Nitrates, especially from smoked products; and sometimes these foods are contaminated with E.coli and salmonella that leads to more damage and more free radical production

  • Various aldehydes formed as a result of lipid peroxidize decomposition

  • Traces of mycotoxins from food like nuts

  • Selenite as source of selenium if used as supplement like sodium selenite, this can stimulate free radical production in the intestine

  • Alcohol

  • The ph and temperature, as well as the presence of oxygen in the stomach, could favour lipid peroxidations that leads to free radical productions

We are also exposed to a variety of factors that increase our free radical production or exposure, Ionizing radiation from the sun that too much exposure may results to free radical production that could result in skin cancer, wrinkles, and cataracts. X-rays, mammograms, CT-scan, and other medical test equipments have a cumulative effect.

High energy radiation is dangerous. It can cause mutations, cancer, atherosclerosis, brain damage, immune system damage, etc. Nearly all high energy radiation causes damage by creating dangerous, highly reactive free radicals. According to Dr. Denham Harman, originator of the free radical theory of aging, we cannot escape free radical damage by avoiding radiation, because chemical reactions in our bodies create free radicals too.

There are many environmental or industrial pollutants that contribute to the burden with toxic metals like mercury, arsenic, lead and others. Smoking and tobacco are among the best to produce free radicals, just a single puff contains literally trillions of free radicals. It could burns away antioxidant vitamins like vitamin C & E and other nutrients. Smoking and tobacco contains potent carcinogens that cause not only inflammation of the lungs and cancer but all sorts of tumor.

Pharmaceutical medications also create free radicals. People with chronic diseases such as diabetes generate more free radicals than a healthy individual. Athletes produce more free radicals as a by-product of exercise. Smoking, alcohol, fried foods, and high fat diets are sources of toxic free radicals.

Not all free radicals are bad. Free radicals produced by our immune system destroy viruses and bacteria. There are free radicals that are involved in producing vital hormones and activating enzymes that are needed for life. We need free radicals to produce energy and various substances that the body requires.

Antioxidant Enzyme System

Our bodies have a built-in antioxidant system that produces natural antioxidants that give us protection against damaging effects of free radicals. These systems are mineral dependent to work efficiently, minerals such as selenium, manganese, zinc and copper are needed to make our enzyme system work and give us protection against free radicals.

These enzyme system include catalase, superoxide dismutase (SOD), and glutathione peroxidase. We need to consume mineral rich foods and/or take mineral supplements to support these enzyme systems. We need to avoid those that deplete us with minerals like distilled water and carbonated drinks.

Our soils in the Philippines are very rich in selenium. We don’t need to worry about food sources and supplements that are rich in selenium, just eat more of locally grown or produced vegetables and fruits to maintain our selenium level in the body. Unlike in America, their soils are selenium-depleted that’s why they need to take supplemental selenium. Just make sure, we take organically grown produce or if not wash thoroughly any fruits and vegetables before eating to minimize exposure to chemical residues.

Manganese, zinc and copper can be obtained by also taking fruits and vegetables especially the dark colored produced. The darker, the more nutrients and the more antioxidant protection we can get.

Liver, kidney, whole grains and nuts are also good sources of manganese. Shellfish, eggs and poultry are good sources of copper as well as organ meats. These foods are also good sources of zinc.

ORAC Value

ORAC stands for Oxygen Radical Absorbance Capacity. It is a method of measuring antioxidant capacities of different foods.

The ORAC test is currently the standardized method used by the USDA for testing foods and supplements anti-oxidant properties. The basic understanding of the ORAC test is that the higher the ORAC value of s food the higher the food's antioxidant level.

The recommended daily antioxidant dose should add up to 5000 ORAC units each day. In reality, 80% of the population is consuming less than 1,000 ORAC units a day. Remember the saying "eat 5 fruits and vegetables a day" and you'll have your needed "vitamins". The truth is that with those servings, you will get an ORAC content of about 1,750 units.

When comparing ORAC data, care must be taken to ensure that the units and food being compared are similar. Some evaluations will compare ORAC units per gram of dry weight, others will evaluate ORAC units in wet weight and still others will look at ORAC units per serving. Under each evaluation, different foods can appear to have higher ORAC values. For example, although a raisin has no more antioxidant potential than the grape from which it was dried, raisins will appear to have a higher ORAC value per gram of wet weight than grapes due to their reduced water content. Likewise, large water content in watermelon can make it appear as though this fruit is low in ORAC. Similarly, the typical quantity of food used should be considered; herbs and spices may be high in ORAC, but are applied in much smaller quantities than for other foods.

Numerous health food and beverage companies and marketers have capitalized on the ORAC rating by promoting products claimed to be "high in ORAC". As most of these ORAC values have not been independently validated or subjected to peer review for publication in scientific literature, they remain unconfirmed, are not scientifically credible, and may mislead consumers.

We have to be very careful when reviewing ORAC values of foods and supplements. First we have to make sure that it states, next to the ORAC score, the unit for the report. You can for example find ORAC scores given per serving, per gram, per 100 grams, etc. This is there were some companies play a game number by not indicating the unit.

Many people and companies use the published ORAC data for comparison purposes but according to Brunswick Laboratory, the leader in ORAC testing, it is not proper to compare products based on ORAC Value. We can used that to compare fruits or vegetables themselves but not products made from them. Different processes will create different results for two products using the same fruit or vegetable.

The ORAC value was not meant to be used as a comparison point between different products! Due to the limited sample sizes and varieties, the published ORAC values of vegetables and fruits are not comprehensive. Importantly, the most published ORAC results are obtained using the old method; therefore they are not valid anymore. Furthermore, the naturally occurring antioxidants actually are the secondary metabolites of natural products; Mother Nature has a profound influence on their biosynthesis pathways. For instance, the geographic locations, weather conditions and the varieties of the species have been determined to influence the antioxidant property chemically and physiologically.

The United States Department of Agriculture create and publish a general list of food items sorted by their antioxidant power. The USDA tested the fruits or vegetables themselves and not products made with them. The ORAC value was intended to be used as internal quality control for companies to make sure that from one batch of a product to another, the anti-oxidant properties are not degrading.

Antioxidants work synergistically in giving protection against free radical damage, so it is better to take smaller doses of several different antioxidants than a large amount of only one.

Fruits and Berries are the most common and excellent source of antioxidants.

Antioxidant Foods

1. Garlic and Allium Family

Garlic contains sulfhydryl (sulfur and hydrogen) compounds that are potent chelators of toxic heavy metals to be excreted in our body by binding to them. These are also effective protectants against oxidation and free radicals. Garlic helps in the detoxification of peroxidases like hydrogen peroxide and in the oxidation of fats. It also contains vitamin A and C.

Garlic, onions, leeks and chives contain flavonoids that stimulate the production of glutathione (the tripeptide that is the liver's most potent antioxidant). Glutathione enhances elimination of toxins and carcinogens, putting the Allium family of vegetables at the top of the list for foods that can help prevent cancer.

Other benefits of garlic

  • Lowers total cholesterol (but raises HDL—"good"—cholesterol)

  • Lessens the risk of atherosclerosis (hardening of the arteries)

  • Lowers blood pressure

  • Reduces the risk of blood clots (cause of the majority of strokes and heart attacks)

  • Destroys infection-causing viruses and bacteria

  • Reduces the risk of certain cancers, in particular, stomach cancers

  • Produces more "natural killer" cells in the blood to fight tumors and infections

  • Helps fight against neurological diseases such as Alzheimer's

2. Acai Berry

The acai berry is an inch-long reddish, purple fruit. It comes from the acai palm tree (Euterpe oleracea), which is native to Central and South America. Açaí is packed full of antioxidants, amino acids and essential fatty acids.

Research has shown that in addition to the anthocyanins and essential fatty acids, acai also contains a healthy dose of plant sterols, another class of phyto-chemicals that have been shown to reduce cholesterol, protect the immune system, and relieve prostate enlargement.

The fatty acid content in açaí resembles that of olive oil, and is rich in monounsaturated oleic acid. Oleic acid is important for a number of reasons. It helps omega-3 fish oils penetrate the cell membrane; together they help make cell membranes more supple. By keeping the cell membrane supple, all hormones, neurotransmitter and insulin receptors function more efficiently. This is particularly important because high insulin levels create an inflammatory state, and we know, inflammation causes aging.

3. Barley

Barley is a low-glycemic grain, it is high in both soluble and insoluble fiber. Soluble fiber helps the body metabolize fats, cholesterol and carbohydrates, and lowers blood cholesterol levels. Insoluble fiber—commonly called "roughage"—promotes a healthy digestive tract and reduces the risk of cancers affecting it (e.g., colon cancer).

Barley is sold in many forms, all of which are nutritious. But hulled barley, in which the outer hull (the bran) is left intact, is richer in fiber and contains more fiber and nutrients than other forms, such as pearl barley or Scotch barley. Eating hulled barley on a regular basis:

  • Lowers blood cholesterol levels

  • Protects against cancer because its high fiber content helps speed food through the digestive tract, and because its a good source of selenium, shown to significantly reduce the risk of colon cancer

  • Is a good source of niacin, the B vitamin that is cardio-protective

  • Slows starch digestion, which may help keep blood sugar levels stable

  • Provides high concentrations of tocotrienols, the "super" form of Vitamin E

  • Provides lignans, phytochemicals that function as antioxidants. Women who consume lignans (also present in high levels in flaxseed) are less likely to develop breast cancer.

4. Beans and Lentils

Beans are low in fat (except for soybeans), calories, and sodium, but high in complex carbohydrates and dietary fiber, and they offer modest amounts of essential fatty acids—mostly omega-6s (only soybeans have significant amounts of omega-3 fatty acids). They are also an excellent source of protein, needing only to be combined with grains such as barley or oats to provide all the amino acids necessary to make a complete protein for vegetarians who do not have other sources of protein for their meals.

Beans are extremely beneficial in an anti-diabetes diet because they rank low on the glycemic scale, which means that they do not cause the inflammatory, hunger-inducing spike in blood sugar levels associated with refined grains and baked goods. Beans offer ample fiber (one cup of cooked beans can provide as much as 15 grams of dietary fiber, more than half the recommended “daily value” of 25 grams and are released into the bloodstream slowly, providing energy and satiation for a sustained period.

5. Barley Grass, Wheat Grass and Other Green Foods

“Green foods," referred to a group of foods that includes young cereal grasses like barley grass and wheat grass, as well a blue-green algae known as BGA. Nutritionally, they are close cousins to dark green leafy vegetables, but offer far greater levels of "nutrient density." In other words, an ounce of these concentrated green foods contains much more of the beneficial phytonutrients found in an ounce of green vegetables.

Chlorophyll, the phytochemical that gives leaves, plants and algae their green hues, is the plant equivalent of the oxygen-carrying red pigment hemoglobin in red blood cells. Dietary chlorophyll inhibits disease bacteria and exerts therapeutic effects on bad breath and internal odors.

There is very little nutritional difference between wheat grass and barley grass, although it is important to note that barley grass acts as a free radical scavenger that also reduces inflammation and pain, and wheat grass contains P4D1, a "gluco-protein" that acts like an antioxidant, reducing inflammation. It is also thought to be able to help the body attack cancer cells. You can get cereal grasses in powder or tablet form. Dried cereal grasses are certainly easier to handle than fresh, which must be juiced. However, fresh grass juice contains healthful enzymes not found in dried grass powder, and is likely to be higher in just about every phytonutrient found in cereal grass.

6. Chili Peppers

Peppers—whether sweet bell or hot chili—are members of the plant genus "capsicum" (cap-sih-kum), a term that comes from the Greek word kapto, which means "to bite." All peppers contain compounds called capsaicinoids. This is especially true of chili peppers, which derive their spicy heat—as well as extraordinary anti-inflammatory, analgesic, anti-cancer, heart-healthy effects—from very high levels of capsaicinoids, the most common form of which is capsaicin. In addition to capsaicin, chilies are high in antioxidant carotenes and flavonoids, and contain about twice the amount of vitamin C found in citrus fruits. Almost any dish, from homemade soups, stews and chili to stir fries, salads, and salsas, can benefit from small amounts of hot peppers.

7. Sprouts

Sprouts are a highly nutritious food. Grown locally year round, sprouts are a good source of protein and vitamin C. A sprout is produced when a seed starts growing into a vegetable. Sprouts can grow from the seeds of vegetables, grains, legumes, buckwheat, and beans.

Sprouts vary in texture and taste. Some are spicy (radish and onion sprouts), some are hardy and often used in Asian cuisines (mung bean), while others are more delicate (alfalfa), and add texture and moistness to salads and sandwiches.

Sprouts are a concentrated source of the living enzymes and "life force" that is lost when foods are cooked or not picked fresh from your own garden. Additionally, due to their high enzyme content, sprouts are also much easier to digest than the seed or bean from which they came.

All nutrients necessary for life are contained in seeds—a food category that includes grain kernels, beans, legumes, and nuts. Because sprouts are so fresh, and do not sit for days or weeks in warehouses, we know that we are getting optimum nutrition.

8. Green Tea

Green tea contains polyphenols, including phytochemicals that have antioxidant, antibacterial, antiviral, and health enhancing properties.

Epigallocatechin gallate (EGCG), a polyphenol in green teahave shown that it is able to penetrate the body’s cells and shield DNA from hydrogen peroxide, a potent free radical.

Green tea protects against cancer, lower cholesterol levels, and reduces the clotting tendency of the blood.

Antioxidant supplements

1. Glutathione

Glutathione is an antioxidant that helps in slowing down the oxidation of substances, thereby protecting the body's cell from harmful effects of free radicals. Chemically, it is a protein made up of three basic amino acids - cysteine, glycine, and glutamic acid. There are two forms of glutathione, namely, reduced-type (monomer) and oxidized-type (dimer). The former is the active type, whereas the latter is acted upon by reductase enzyme to convert into active molecules.

Glutathione is synthesized by the human body on its own, and it is present in every cell including those of the immune system. During the synthesis of glutathione, the body first extracts the three amino acids from the food items. The amino acids are then combined to form glutathione. Medical researches have revealed that this antioxidant regulates the functioning of the immune system and stimulates the generation of lymphocytes (present in white blood cells). A deficiency of this antioxidant may lead to nervous system disorders such as lack of coordination and mental problems, while speeding up the process of aging.

Food items that contain high amounts of glutathione are asparagus, orange, grapefruit, watermelon, potato, tomato, strawberries, spinach, cabbage, parsley, broccoli, and meat. Whey protein is another rich source of glutathione. This antioxidant is available commercially as a dietary or nutritional supplement in the form of white powder. One of the drawbacks of this antioxidant supplement is that there is no significant effect of external or oral administration of glutathione in the intracellular level. The gastrointestinal tract of humans does not absorb glutathione, when taken orally. Some studies claim that ingestion of glutathione supplement in a high dose (about 3 grams) can raise the intracellular level. An effective method of increasing glutathione in the body is by means of intravenous injections.

According to studies, patients with cancer, heart disease, and other chronic health problems show comparatively lower amount of glutathione than a normal healthy person. Considering this, glutathione supplement is prescribed for treating various diseases and disorders. Some of the common diseases treated by using glutathione antioxidant are cancer, eye problems (especially cataract), Parkinson's disease, heavy metal poisoning, Alzheimer's disease, HIV, and infertility. Apart from these, some people opt for this antioxidant to detoxify the body, whiten skin, and improve the overall health. Very often, physicians recommend glutathione inhalation for treating airway restriction.

Similar to other dietary supplements, those containing glutathione may cause certain adverse effects. Possible side effects of glutathione supplements are difficulty in breathing, tightness in the chest, chest pain, and other allergic reactions such as itching, hives, skin inflammation, etc. An individual allergic to dietary supplements should abstain from glutathione. As there is no standard regulation for manufacturing nutritional supplements, it is always advisable to purchase dietary products containing glutathione from reliable sources. This simple approach will help in avoiding unpredictable results. Also, make sure to check the label for any additives like sugar, starch, and silica in the product.

A far as restriction of glutathione supplement is concerned, this product is not recommended for pregnant women, those planning a pregnancy, and breastfeeding mothers. Patients of hypertension, heart disease, and those with a compromised immune system should not ingest glutathione without the supervision of a qualified physician. To be on the safer side, one should incorporate glutathione rich foods in the diet plan instead of relying on the antioxidant supplements. This will help in preventing the potential side effects of taking excess glutathione.

2. Acai Berry Juice

Acai berry is becoming a popular ingredient in many nutritional supplements on the market. Many health experts agreed that the Acai berry was the number one super food in the world. The Acai berry has also been featured on Oprah, Wall Street Journal. There are a variety of ads and publications praising the many health benefits that the Acai berry offers. Experts agree that the Acai berry seems to be one of the most nourishing natural foods found on Earth today. The Acai berry can help you stay young and healthy while feeling your best.

Acai berries are harvested in the rainforests of Brazil and taste like a combination of berries and pomegranate. It has a sweet and tangy flavor with undertones of bitter dark chocolate. Although most berries have antioxidant properties, the Acai berry is packed with antioxidants, amino acids and essential fatty acids. The small purplish blue berry has become a popular choice for detoxing and maintaining the pH levels of the body which improves the immune system.

The acai berry is gaining so much popularity because of its nutritional properties which not only purge the body of free radicals which prematurely age the body but this little berry also provides much of the essential vitamins and minerals that the body depends on everyday. The acai berry packs in plenty of omega fatty acids, amino acids, fiber and iron.

Brazilian natives have been eating acai berries for hundreds of years and they revere the fruit for its healing powers. The essential fatty acids found in the acai berry coupled with omega fatty acids are known to lower cholesterol levels. They also combat the free radicals floating around within the body causing premature aging.

As a dietary supplement acai berry works by providing the body with protein, unsaturated lipids and carbohydrates. This is the recipe for energy and muscle building an asset for any diet and exercise regiment. Many Brazilian sports clubs, gyms and beach resorts serve acai berries for this specific reason. It is a health addition to any muscle sculpting and weight loss regiment.

Health Benefits

  • Better Digestion

  • Better Mental Health

  • Detoxification

  • Healthier Skin

  • Healthy Heart

  • Improved Circulation

  • Improved Sleep Cycle

  • More Energy

  • Stronger Immune System

  • Weight Loss

  • Youthful Appearance

3. Coenzyme Q10

Coenzyme Q10 is a naturally-occuring compound found in every cell in the body. Coenzyme Q10's alternate name, ubiquinone, comes from the word ubiquitous, which means "found everywhere."

CoQ10 plays a key role in producing energy in the mitochondria, the part of a cell responsible for the production of energy in the form of ATP.