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what are free radicals including the free radicals definition and free radical theory of cancer

Free radicals and oxidative stress have been linked to some of the top leading causes of death in America including cancer, diabetes, and cardiovascular diseases.

Free Radicals

In the past few years, an increasing amount of health news has focused on the potential dangers of free radicals. They are often discussed alongside cancer, and are considered a complex factor in disease development.

But many of us lack a clear understanding as to what are free radicals exactly and how do they play a role in our everyday health.

The most common free radicals’ definition is any unstable molecule with one or more unpaired electrons which is formed through normal cell metabolism.1,3

Free radicals are also highly reactive and are associated with many disease states. They can lead to the formation of larger groups, also known as reactive oxygen species (ROS). These groups cause DNA damage and other harmful effects.1

Where Do Free Radicals Come From?

For all the discussion on the importance of free radicals, how are free radicals formed is often not highlighted. Free radicals can be formed by internal or external sources. Below, we take a look at some of the most common examples of free radicals.

Does exercise cause free radicals? – Exercise has been shown to be a source of internally generated free radicals and short term oxidative stress.1

Internal Free Radicals
Within the body, free radicals are produced though natural metabolic processes, such as converting food into energy.1 Internal sources may also include inflammation, or reperfusion injuries.1

Alcohol and Free Radicals
According to the National Institute on Alcohol Abuse and Alcoholism, with increased consumption of alcohol, free radicals become more active and are produced in increased amounts. Alcohol appears to reduce levels of antioxidants, which help neutralize free radicals and are a part of the body’s natural defense.4

Foods and Free Radicals
While many health foods contain antioxidants that work to neutralize free radicals, some foods may promote free radicals to form in the body. Wondering what foods cause free radicals and how to avoid them? The simple answer is to be aware of what kind of cooking oil you are using. According to the Cleveland Clinic, the type of oil we cook with can make both a nutritional and health difference. While all oils have an oxidation rate, some are lower than others and considered healthier. Oxidation promotes increased free radicals to form and may contribute to our overall exposure.6

Mental Stress and Free Radicals
The connection between mental stress and free radicals is also becoming increasingly clear. Recent findings have established a connection between oxidative stress in the brain and anxiety disorders, depression and nervous system impairment.7

External Sources of Free Radicals
Common external sources of free radicals include radiation, cigarette smoke, select drugs, X-rays, and environmental pollutants. Pesticides and industrial solvents are also considered external sources and may leave free radicals on skin exposed to the products.1

Free Radical Theory

The free radical theory of aging has come to light in recent years as a way to explain how free radicals may influence our long-term health. The free radical theory proposes that the human life span is dependent on cumulative levels of free radicals and antioxidants in the body. It explains that as we age, the number of free radicals in the body increases and causes DNA and oxidative damage at a cellular level.1,2 Research has noted that free radicals have a significant influence on the aging process and Functional DNA damage is linked to the aging process, along with several disease states.

Thus, increased levels of free radical scavengers, also known as antioxidants are believed to protect proper cell function and promote longevity.2

However, aging is a multi-faceted process, that is caused by many factors. While one of the most popular theories of aging, it does not establish a definitive relationship and cannot be described as the only cause of aging.

Why are Free Radicals Bad?

In the body, free radicals attack proteins, lipids and nucleic acids.1 While scientists are still investigating how the free radical mechanism works, it can promote DNA impairment, proteins becoming cross-linked and increase age pigmentation (cellular wear and tear) on important organs.2

Excessive levels of ROS have been connected to various human conditions, such as: diabetes, cardiovascular diseases, Parkinson’s disease, Alzheimer’s disease, various forms of cancer, cataracts, inflammation and emphysema.1,4

When individuals are exposed to constant internal or external sources of free radicals, it can accumulate into oxidative stress, an imbalance of potential harmful free radicals and antioxidants. Chronic oxidative stress can lead to increased production of harmful ROS.1

Free Radicals and Cancer

Beyond causing cell death, how do free radicals cause cell damage? Free radicals have been shown to cause permanent damage to the DNA. It’s believed that with chronic increases of free radicals, cancer development may become more likely. Increasing research shows that free radicals not only promote carcinogenesis, but may also be associated with cancer progression.1,7

The free radical theory of cancer suggests that individuals can reduce the risk of harmful free radicals and disease by increasing dietary antioxidants, practicing caloric restriction and minimizing foods that promote free radical reactions, such as polyunsaturated fats.8

Examples of free radicals including alcohol free radicals and what foods cause free radicals

Free radicals can come from a variety of everyday sources. Help prevent free radical damage by boosting antioxidants and reducing exposure to external harmful chemicals.

How to Avoid Free Radical Damage

Often, exposure to external sources of free radicals such as x-rays and environmental toxins are a part of everyday life. Although we have limited control over some free radical sources, one of the most effective ways individuals can take matters into their own hands is by increasing their free radical protection. For the most effective ways to reduce free radical damage, consider these six, easy lifestyle changes to strengthen your antioxidant defenses.

1. Free Radical Scavenger Supplements

Free radical scavenger supplements help boost antioxidant defenses and deliver nutrients that users may not be receiving through diet alone. Numerous studies show that antioxidant micronutrients like vitamin E, vitamin C and β-carotene have been shown to beneficially affect the risk of cardiovascular disease.9

How do antioxidant minerals stabilize free radicals? – In the body, antioxidants fight free radicals by acting as scavengers that help prevent tissue and DNA damage caused by free radicals. They also help prevent the formation of free radicals and the oxidation of unsaturated fats.1

2. Antioxidant-Rich Foods

Antioxidants can be derived from synthetic or natural sources. Since natural sources are more stable and preferred, there’s a growing interest in foods that reduce free radicals. Research has shown that various fruits and berries such as cherries, acai, prunes and some citrus fruits have notable antioxidant activity. Vegetables such as carrots, broccoli and tomatoes also contain a variety of beneficial active compounds.1

Various plants used in Ayurveda, such as Indian aloe vera, onion and garlic have been noted to contain antioxidants. Additionally, green and black tea have been extensively studied for their antioxidant properties.1

3. Avoid Smoking and Second-Hand Smoke

Cigarette smoke has been identified as a direct cause of free radical exposure and has even been shown to contain not one, but two different types of free radicals. In vitro studies have noted that the tar in cigarettes react with DNA and promote lipid oxidation.5 Lower levels of antioxidants have also been recorded in individuals exposed to second-hand smoke.10

4. Drink in Moderation

In the body, alcohol has been shown to stimulate enzymes that contribute to free radical damage. When this occurs in liver cells, it can play a key role in promoting alcoholic liver disease.4 Limiting the consumption of alcohol is a simple lifestyle choice that can keep your body healthy.

5. Use Natural Cleaners and Pesticides

To lower your exposure to external free radicals, avoid using harsh, chemical cleaners and pesticides. At low levels, even common cleaners such as hydrogen peroxide can cause DNA damage.11 Instead, reach for all-natural cleaners to avoid increased exposure.

6. Eat Organic Food

External free radicals can come in a variety of forms and can build up in our bodies over repeated exposure. Ongoing animal research has identified that deltamethrin, a pesticide used in agriculture and urban settings, increases free radical formation and damage in the brain.12 Switching to organic foods help limit exposure to potentially harmful pesticides. Fruits and vegetables without a protective layer, such as apples, spinach or strawberries are more likely to be exposed to pesticides. Each year, produce is ranked by the Environmental Working Group (EWG) who creates the ‘Dirty Dozen’ list, the top 12 fruits and vegetables that rank highest for levels of pesticide.13 Switching to organic produce helps reduce ongoing exposure to these pesticides.

7. Use Healthy Cooking Oils

When it comes to cooking, chefs should think twice about the oils they use. When cooking, oils become oxidized and promote free radical formation in the body. To combat this, choose oils that contain natural antioxidants and healthy fats. Extra-virgin olive oil is recommended as one of the oils with a low oxidation rate.6Oils high in trans-fat are considered to have higher oxidation rates and should be avoided.

Take it one step further by sautéing foods rather than deep frying to reduce free radical exposure. Making sure oil is fresh and stored in a cold, dark place can also reduce the rate of oxidation.7

Scientific Research Referenced in this Article

  1. Lobo, V., Patil, A., Phatak, A., & Chandra, N. (2010). Free radicals, antioxidants and functional foods: Impact on human health. Pharmacognosy Reviews4(8), 118. doi:4103/0973-7847.70902
  2. Wickens, A. P. (2001). Ageing and the free radical theory. Respiration Physiology128(3), 379-391. doi:1016/s0034-5687(01)00313-9
  3. National Cancer Institute. (n.d.). NCI Dictionary of Cancer Terms – Free radical. Retrieved September 26, 2017 from https://www.cancer.gov/publications/dictionaries/cancer-terms?cdrid=44030
  4. Wu, D. & Cedarbaum, A.I. (2004). Alcohol, Oxidative Stress, and Free Radical Damage. National Institute on Alcohol Abuse and Alcoholism. Retrieved September 26, 2017 from https://pubs.niaaa.nih.gov/publications/arh27-4/277-284.htm
  5. Church, D. F., & Pryor, W. A. (1985). Free-Radical Chemistry of Cigarette Smoke and Its Toxicological Implications. Environmental Health Perspectives64, 111. doi:2307/3430003
  6. Cleveland Clinic. (2014, June 3). 7 Things You Should Know About Cooking With Oil. Retrieved October 4, 2017 from https://health.clevelandclinic.org/2014/06/7-things-you-should-know-about-cooking-with-oils/
  7. Dreher, D., & Junod, A. (1996). Role of oxygen free radicals in cancer development. European Journal of Cancer32(1), 30-38. doi:1016/0959-8049(95)00531-5
  8. Black, H. S. (2004). Reassessment of a Free Radical Theory of Cancer With Emphasis on Ultraviolet Carcinogenesis. Integrative Cancer Therapies3(4), 279-293. doi:1177/1534735404270612
  9. Kris-Etherton, P. M. (2004). Antioxidant Vitamin Supplements and Cardiovascular Disease. Circulation110(5), 637-641. doi:1161/01.cir.0000137822.39831.f1
  10. Office of Smoking and Health (2006). MORITSUGU, K. (2007). Toxicology of Secondhand Smoke In The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Retrieved November 20, 2017 from https://www.ncbi.nlm.nih.gov/books/NBK44321/
  11. Phaniendra, A., Jestadi, D. B., & Periyasamy, L. (2014). Free Radicals: Properties, Sources, Targets, and Their Implication in Various Diseases. Indian Journal of Clinical Biochemistry30(1), 11-26. doi:1007/s12291-014-0446-0
  12. Li, H., Wu, S., Ma, Q., & Shi, N. (2011). The pesticide deltamethrin increases free radical production and promotes nuclear translocation of the stress response transcription factor Nrf2 in rat brain. Toxicology and Industrial Health27(7), 579-590. doi:1177/0748233710393400
  13. Pou, J. (2010, May 13). The dirty dozen and clean 15 of produce. Retrieved November 20, 2017 from http://www.pbs.org/wnet/need-to-know/health/the-dirty-dozen-and-clean-15-of-produce/616/
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