Free radicals are molecules that freely attack other molecules and cause radical alteration to the stability and function of cells. Understanding these chemical interactions can shed light on how pollutants, pesticides and drugs can be detrimental to health.
Don't worry – we'll keep it simple:
Quick Chemistry Refresher
Atoms have protons and neutrons at the centre, surrounded by orbiting electrons*. It's the interaction of electrons that creates chemical reactions and these small particles bond atoms together to form molecules. When electrons interact, molecules are formed. Molecules bond together to form cells, and cells form the human body.
Zooming back in to the molecular level, you can imagine atoms as a shell. Each shell can hold a certain number of electrons, and they fill up from the central shell (closest to the protons and neutrons) outwards. If the outer shell of an atom contains the maximum number of electrons it can hold, then that atom is stable. It's happy, fulfilled, and is unlikely to interact with other atoms.
However, if the outer shell isn't full, the atom is unstable. The electrons in the unfilled outer shell are said to be unpaired. All atoms want to be stable and they'll do anything to get that way [7][8].
Depending on the number of electrons and which shell is involved, the atom will:
- Give away electrons so that its outer shell becomes empty, thereby making the next-shell-down the full, stable shell
- Take electrons from other atoms to fill its outer shell
Or
- Bond with another atom by share electrons with it, forming a molecule.
(* Science has discovered that quarks and quasars are involved on an even deeper level, but we're years away from understand how they affect electron charges or human health!)
The Birth of Free Radicals
Once atoms are bonded together to form molecules, they don't normally split apart in a way that leaves an unpaired electron. But it does happen – weak bonds can split and result in unstable, highly reactive molecules called free radicals. These molecules are volatile and relentless, and their charge is strong. Free radicals will react with the nearest molecule and take its electron. The molecule it reacts with will lose an electron from its outer shell in this exchange, and become a free radical itself. This process cascades from molecule to molecule and can eventually disrupt the function of a living cell – free radical cascades affect lipids, proteins, and DNA within the body [7][8].
Types of Free Radicals
Radicals are defined as containing at least one unpaired electron. These include:
- Nitrogen dioxide [10]
- Superoxide ion radical
- Oxygen radical
- Hydroxyl radical
- Alkoxyradical
- Peroxyl radical
- Nitric oxide (nitrogen monoxide)
There are other compounds that are not technically free radicals but can easily cause a cascade of free radical activity in the body.
These include:
- Singlet oxygen molecules
- Hydrogen peroxide
- Ozone
- Peroxynitrite
- Nitroxyl anion [10]
Where Do Free Radicals Come From?
Free radicals are created in normal metabolic processes such as:
- Energy production.
- Immune cells create free radicals to attack pathogens.
- The P-450 liver detoxification pathway.
- Inflammatory processes. [10]
Generally speaking, the free radicals produced by these processes are for the benefit of the body and are quickly balanced out by antioxidant activity or further metabolism. However, exposure to environmental free radicals can tip the scales and cause an imbalance, leading to a cascade of free radical activity.
Environmental free radicals include:
- Industrial chemicals
- Pollution
- Radiation (e.g. UV, x-rays, gamma radiation when flying)
- Cigarette smoke
- Some medications and recreational drugs
- Pesticides and herbicides
- Alcohol [8][9]
Oxidative Stress – How Free Radicals Cause Disease
Oxidative stress is a term for an imbalance of free radical activity in the body. When free radical cascades overpower the available reserves of antioxidants, damage is unstoppable and cell function becomes impaired and can even shut down completely. When a number of cells are affected, health of the body tissue or organ can become compromised. An escalation of oxidative stress naturally occurs as the body ages but further acceleration can cause disease.
Some diseases that involve oxidative stress include:
- Atherosclerosis: A hardening of the arteries occurs when cholesterol and artery walls come under free radical attack. Heart disease, stroke and high blood pressure also involve oxidative stress [10].
- Cancer : Research on cancer suggests it may be a “free radical disease” because cell signalling and regulation of cell growth can be disturbed when free radicals damage DNA [2][3][5] [10].
- Inflammatory diseases : Free radicals are involved in inflammatory diseases including arthritis, lupus erythematous, and asthma [10].
- Neurological disorders: Alzheimer's disease, M.S., Parkinson's disease and muscular dystrophy may involve damage from oxidative stress [10].
It's not all bad news – free radicals can be stopped!
How Antioxidants Stop Free Radicals
You've heard of acai, blueberries and turmeric – foods that are rich in nutrients that act as free radical scavengers. These nutrients are called antioxidants. Not all antioxidants are nutrients, but many are. Antioxidants neutralise the activity of a free radicals via a few different mechanisms including:
Electron donation. Some antioxidants stop the free radical cascade by donating an electron, giving the free radical what it wants, and stabilising the molecule so it doesn't cause any further damage. Despite donating an electron, antioxidants don't become free radicals themselves because their core is more stable than a free radical's.
Hydrogen donation. Similar to electron donation, but these antioxidants donate a hydrogen atom to create a strong bond with the free radical, neutralising it and making it non-reactive.
Decomposing peroxides. Some larger antioxidant molecules can initiate chemical reactions that decompose some free radicals into lipids or water.
Thioredoxin System. Thioredoxins are small proteins that support DNA and protein repair following oxidative stress. [10] [11]
(* Did you know that the sleep molecule, melatonin, is an antioxidant?)
Five Key Antioxidant Nutrients
Before we get into our top 5 powerful nutrients, be aware that all antioxidants work as a team. Research has shown that antioxidants are at their best when working in combination with each other, rather than as individual supplements.
Vitamin E – Abundant and highly effective, vitamin E is a fat-soluble antioxidant that can act in fatty environments like the brain to protect against oxidative damage and lipid oxidation.
Vitamin C – This vitamin is severely underrated and one of the best free radical scavengers in existence. It is the most abundant water-soluble antioxidant in the human body, and is particularly effective against free radical damage from cigarettes and pollution.
Carotenoids – These types of nutrients, including beta-carotene and astaxanthin, show powerful singlet oxygen quenching activity. Many anti-ageing beauty products include carotenoids, as some signs of ageing are due to the increase of oxygen species of free radicals after UVA sun exposure.
As carotenoids quench the oxygen species, they may act as key anti-ageing nutrients [1].
Flavanoids – This class of antioxidants are found in all fruits and vegetables. Key flavanoids include quercetin from apples and onions, genestein from soy, resveratrol from red wine, and anthocyanins from blueberries. Along with carotenoids, they are responsible for the rich colours of plants and quenching free radicals throughout the body. Research has shown the antioxidant effects of diets rich in flavonoids may protect against ovarian cancer [2], oesophageal cancer [3], non-Hodgekin's lymphoma [4], and colorectal cancer [5].
Polyphenols - Ferulic acid from brown rice and coffee, chologenic acid in tomatoes, and salicylic acid found in most vegetables have all been shown to act as antioxidants by scavenging singlet oxygens and hydrogen peroxide molecules. Research suggests that polyphenol foods may help to prevent chronic disease onset [6].
Other antioxidant nutrients include selenium, leutine, lycopene, allyl sulphides, and many, many more! The best way to keep your free radicals in balance is to eat a diet rich in colourful fruits and veggies.
References
- Terero, J., et al. (2010) Singlet molecular oxygen-quenching activity of carotenoids: relevance to protection of the skin from photoaging. J Clin Biochem Nutr., 48:1, 57 – 62. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3022065/
- Hua, X. (2016) Association among Dietary Flavonoids, Flavonoid Subclasses and Ovarian Cancer Risk: A Meta-Analysis. PLoS ONE, 11:3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4784737/
- Cui, L., et al. (2016) Flavonoids, Flavonoid Subclasses, and Esophageal Cancer Risk: A Meta-Analysis of Epidemiologic Studies. Nutrients, 8:6, 350. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4924191/
- Frankenfeld, C. L., et al. (2008) Dietary flavonoid intake and non-Hodgkin lymphoma risk. American Society for Clinical Nutrition, 87:4, 1439 – 1445. http://ajcn.nutrition.org/content/87/5/1439.full
- He, X. & Sun, L. (2016) Dietary intake of flavonoid subclasses and risk of colorectal cancer: evidence from population studies. Oncotarget, 7:18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042003/
- Pandey, K. B. & Rizvi, S. I. (2009) Plant polyphenols as dietary antioxidants in human health and disease. Oxid Med Cell Longev., 2:5, 270 – 278. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2835915/
- Pham-Huy, L. A., et al. (2008) Free Radicals, Antioxidants in Disease and Health. Int J Biomed Sci., 4:2, 89 – 96. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3614697/
- Lobo, V., et al. (2010) Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Review., 4:8, 118 – 126. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/
- Rahman, K. (2007) Studies on free radicals, antioxidants, and co-factors. Clin Interv Aging., 2:2, 219 – 236. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684512/
- Phaniendra, A., et al. (2015) Free Radicals: Properties, Sources, Targets, and Their Implication in Various Diseases. Indian J Clin Biochem., 30:1, 11 – 26. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4310837/
- Lu, J. & Holmgren, A. (2014) The thioredoxin antioxidant system. Free Radical Biol Med., 66, 75 – 87. https://www.ncbi.nlm.nih.gov/pubmed/23899494
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