Free radicals, reactive oxygen and nitrogen species (RONS)
A free radical is basically a molecule with an unpaired electron. Since electrons like to travel in pairs, a molecule with one missing is highly reactive and may treat to ‘steal’ electrons from elsewhere. Free radicals are highly unstable molecules that are naturally formed when we exercise and when our body converts food into energy, which can cause damage to biological molecules and cell structures, such as proteins, lipids, DNA and cell membranes. While the body does need some free radicals to function, if there are too many built up in a person’s system then the damage can become irreparable and may lead to diseases such as cancer, cardiovascular disease, liver disease, and many others.
About 60 years ago the discovery of reactive oxygen species (ROS) in biology started an era in which the scientific community’s attempt to understand the impact of the unpaired electron of ROS molecules in biological pathways, which were eventually noted to be harmful.
ROS are a group of small reactive molecules that play key roles in the regulation of various cell functions and biological processes. In the vascular system, physiological levels of ROS are essential for normal vascular functions including endothelial homeostasis and smooth muscle cell contraction.
While free radicals are any atom with an unpaired electron, ROS are all the free radicals that are commonly found in biology that involve oxygen. So ROS’s are free radicals, specifically involving oxygen.
Nowadays is known that the formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism, and that RONS also act as messengers via redox regulation of essential cellular processes. RONS are produced in biological system because of redox reactions. The imbalance in pro-oxidant and antioxidant homeostasis leads to the production of toxic RONS like hydrogen peroxide, organic peroxides, hydroxyl radicals, superoxide anion and nitric oxide. Inactivation of metabolic enzymes, oxidation of biomolecules and cellular damage are some of the prominent characteristics of RONS.
While certain levels of free radicals and RONS result from normal metabolism, some factors such as smoking, poor diet, and exposure to radiation, air pollution, sunlight, solvents, among others, can increase the formation of free radicals. Uncontrolled overproduction of RONS results from an imbalance of their generation and elimination. Excessive ROS cause vascular cell damage. Evidence from a large number of studies has revealed that ROS and oxidative stress are involved in the initiation and progression of numerous vascular diseases including hypertension, atherosclerosis, restenosis and abdominal aortic aneurysm.
Oxidative stress is the result of the imbalance between RONS formation and enzymatic and non-enzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. Oxidative stress is thought to play a role in a variety of diseases including cancer, cardiovascular diseases, diabetes, Alzheimer’s disease, Parkinson’s disease, and eye diseases such as cataracts and age-related maculardegeneration.
The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy.
Oxidative stress and aging
Aging is a complex phenomenon and its impact is becoming more relevant due to the rising life expectancy and because aging itself is the basis for the development of age-related diseases. Recent years of scientific research have brought up different theories that attempt to explain the aging process. So far, there is no single theory that fully explains all facets of aging. The damage accumulation theory is one of the most accepted ones due to the large body of evidence found over the years. Damage accumulation is thought to be driven, among others, by oxidative stress. This condition results in an excess attack of oxidants on biomolecules, which lead to damage accumulation over time and contribute to the functional involution of cells, tissues and organisms. If oxidative stress persists, cellular senescence is a likely outcome and an important hallmark of aging.
Unlike free radicals, antioxidants are stable molecules. They can prevent, reduce or repair the damage caused by free radicals by means of different mechanisms. The toxicity of reactive species is balanced by the integrated antioxidant systems, which include enzymatic and non-enzymatic antioxidants. Antioxidant therapies or defenses protect the biological sites by removing or quenching the free radicals (prooxidants).
Antioxidant molecules have been shown to counteract oxidative stress in laboratory experiments. However, there is controversy as to whether consuming large amounts of antioxidants in supplement form actually benefits health. There is also some concern that consuming certain antioxidant supplements in excessive doses may be harmful. In contrast, vegetables and fruits are healthy foods and rich sources of antioxidants whose intake has not raised safety concerns. Typical antioxidants include vitamins A, C and E, minerals zinc, copper, selenium and manganese, and plant pigments such as flavonoids, anthocyanins and beta-carotene.
But using the term “antioxidant” to refer to substances is not clear at all. It is a chemical property, namely, the ability to act as an electron donor. Some substances may act as antioxidants in one situation, and to be pro-oxidants—electron grabbers—in different chemical milieu. Also, antioxidants are not interchangeable. Each one has unique chemical behaviors and biological properties. They almost certainly evolved as parts of networks, with each different substance (or family of substances) playing slightly different roles. This means that no single substance can do the work of all.
While increased oxidative damage is involved in the pathophysiology of most age-dependent diseases and markers of oxidative damage tend to increase with age, such correlation does not support causality and unfortunately, many intervention trials with antioxidants have failed to extend health span and to prevent diseases.
Experimental and observational studies
Experiments studies have shown that antioxidants interacted with free radicals and stabilized them, thus preventing the free radicals from causing cell damage. These results support the thesis that antioxidants can correct or prevent oxidative stress-related diseases,.
Observational studies on the typical eating habits, lifestyles, and health histories of large groups of people have shown that those who ate more vegetables and fruits had lower risks of several diseases, including cardiovascular disease, stroke, cancer, and cataracts. Observational studies can provide ideas about possible relationships between dietary or lifestyle factors and disease risk, however, they cannot show causal relationships. For example, people who eat more antioxidant-rich foods might also be more likely to exercise and less likely to smoke. It may be that these factors, rather than antioxidants, account for their lower disease risk.
A diet high in antioxidants may reduce the risk of many diseases, including heart disease and certain cancers. Antioxidants scavenge free radicals from the body cells, and prevent or reduce the damage caused by oxidation. The protective effect of antioxidants continues to be studied around the world. For instance, men who eat plenty of the antioxidant lycopene (found in tomatoes) may be less likely than other men to develop prostate cancer. Lutein, found in spinach and corn, has been linked to a lower incidence of eye lens degeneration and associated blindness in the elderly. Flavonoids, such as the tea catechins found in green tea, are believed to contribute to the low rates of heart disease in Japan.
There is increasing evidence that antioxidants are more effective when obtained from whole foods, rather than isolated from a food and presented in tablet form – and some supplements can actually increase cancer risk. For instance, vitamin A (beta-carotene) has been associated with a reduced risk of certain cancers, but an increase in others, such as lung cancer in smokers, if vitamin A is purified from foodstuffs.
A well-balanced diet, which includes consuming antioxidants from whole foods, is best. If you insist on taking a supplement, seek supplements that contain all nutrients at the recommended levels.
Well-designed clinical studies still generate controversial results. Studies involving more than 100,000 people combined have tested whether antioxidant supplements can help prevent chronic diseases, such as cardiovascular diseases, cancer, and cataracts. In most instances, antioxidants did not reduce the risks of developing these diseases. Chronic treatment with antioxidants failed to show benefits in the prevention of diseases or health complications resulting from oxidative stress. On the contrary, some clinical studies have shown that such long-term treatment with certain antioxidants (high doses of Vitamin E, β-carotens in lung cancer) may be harmful. Several factors can be associated to these results, including the following:
- The dual role of RONS in living organisms which have been conformed to the presence of RONS and, in retrospect, have adapted to the bioactive molecules generated by such species on proteins, lipids, and DNA. Also, RONS have undergone a shift from being molecules that invoked oxidative damage in regulating signaling pathways that impact on normal physiological and redox response to be considered as cellular oxidants involved in the maintenance of redox homeostasis in redox regulation of normal physiological functions, while higher levels may have an essential role in several diseases.
- The beneficial health effects of a diet high in vegetables and fruits or other antioxidant-rich foods may actually be caused by other substances present in the same foods, other dietary factors, or other lifestyle choices rather than antioxidants.
- The effects of large doses of antioxidants used in supplementation studies may be different from those of the smaller amounts of antioxidants consumed in foods.
- Differences in the chemical composition of antioxidants in foods versus those in supplements may influence their effects.
- For some diseases, specific antioxidants might be more effective than the ones that have been tested. So, to prevent eye diseases, antioxidants that present in the eye, such as lutein, might be more beneficial than those not found in the eye, such as beta-carotene.
- The relationship between free radicals and health may be more complex than has previously been thought. Under some circumstances, free radicals actually may be beneficial rather than harmful, and removing them may be undesirable.
- The methods used to evaluate oxidative stress in humans, with lack of consensus concerning the validation, standardization, and reproducibility of methods which assess: RONS in leukocytes and platelets by flow cytometry; markers based on RONS-induced modifications of lipids, DNA, and proteins; enzymatic players of redox status, and total antioxidant capacity of human body fluids, being suggested that should be better to use indexes of oxidative stress that include more than one marker.
In light of these facts, the clinical usefulness of taking antioxidant supplements in general is under debate.
Sources of antioxidants
Some antioxidants are produced in the body, but many are not and need to be obtained through the diet. Antioxidants are found in a number of foods and may prevent free radicals from damaging your cells some of the damage caused by free radicals by neutralizing them. These include the nutrient antioxidants, vitamins A, C and E, and the minerals copper, zinc and selenium.
Other dietary food compounds, such as the phytochemicals in plants, are believed to have greater antioxidant effects than vitamins or minerals. These are called the non-nutrient antioxidants and include phytochemicals, such as lycopenes in tomatoes and anthocyanins found in cranberries.
Vegetables and fruits are rich sources of antioxidants. There is good evidence that eating a diet that includes plenty of vegetables and fruits is healthy. Research has shown that people who eat more vegetables and fruits have lower risks of several diseases; however, it is not clear whether these results are related to the amount of antioxidants in vegetables and fruits, to other components of these foods, to other factors in people’s diets, or to other lifestyle choices.
Good sources of specific antioxidants include: allium sulphur compounds ( leeks, onions and garlic); anthocyanins (eggplant, grapes and berries); beta-carotene (pumpkin, mangoes, apricots, carrots, spinach and parsley); catechins ( red wine and tea); copper ( seafood, lean meat, milk and nuts); cryptoxanthins (red capsicum, pumpkin and mangoes); flavonoids (tea, green tea, citrus fruits, red wine, onion and apples); indoles (cruciferous vegetables such as broccoli, cabbage and cauliflower); isoflavonoids (soybeans, tofu, lentils, peas and milk); lignans (sesame seeds, bran, whole grains and vegetables); lutein (green, leafy vegetables like spinach, and corn); lycopene (tomatoes, pink grapefruit and watermelon); manganese (seafood, lean meat, milk and nuts); polyphenols – (thyme and oregano); selenium (seafood, offal, lean meat and whole grains); vitamin A (liver, sweet potatoes, carrots, milk, and egg yolks); vitamin C (oranges, blackcurrants, kiwifruit, mangoes, broccoli, spinach, capsicum and strawberries); vitamin E (vegetable oils, such as wheat germ oil, avocados, nuts, seeds and whole grains); zinc (seafood, lean meat, milk and nuts)
High-dose antioxidant supplements may be harmful in some cases. For example, the results of some studies have linked the use of high-dose beta-carotene supplements to an increased risk of lung cancer in smokers and use of high-dose vitamin E supplements to increased risks of hemorrhagic stroke (a type of stroke caused by bleeding in the brain) and prostate cancer. Not all trials of beta-carotene show this harmful effect, however. In the Physicians’ Health Study, which included few active smokers, no increase in lung cancer or any other adverse effect was seen even after 18 years of follow-up.
Like some other dietary supplements, antioxidant supplements may interact with certain medications. For example, vitamin E supplements may increase the risk of bleeding in people who are taking anticoagulant drugs (“blood thinners)
It is recommended that people eat a wide variety of fresh fruits, vegetables, whole grains, lean meats and dairy products every day. Your diet should include five daily serves of fruit and vegetables. It is also considered that antioxidants and other protective constituents from vegetables, legumes and fruits need to be consumed regularly from early life.
Do not use antioxidant supplements to replace a healthy diet or conventional medical care, or as a reason to postpone seeing a health care provider about a medical problem.
If you are considering a dietary supplement, first get information on it from reliable sources. Keep in mind that dietary supplements may interact with medications or other supplements and may contain ingredients not listed on the label
In all cases, tell all and request advisement from your health care providers.
Oxidation in the body can produce free radicals and RONS which attack lipids, proteins, DNA, cell membranes and organs. Antioxidants in the diet may help counteract such action. The link between oxidative stress and a group of diseases is proven. Experimental studies have demonstrated the benefits of administered antioxidants against oxidative stress-induced cell damage, but clinical studies have failed to find benefits for lowering the risk of chronic diseases. New research is still ongoing on such regard. not proven from different sources. Keep in mind that the important thing is to maintain a healthy lifestyle, including a diet with abundant vegetables and fruits, among other nutrients. In some cases, taking supplements may also be helpful, but should preferably be done under the guidance of a healthcare practitioner.
Albanes D, Heinonen OP, Taylor PR, et al. Alpha-tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance. J Natl Cancer Inst. 1996; 88:1560-70
Hercberg S, Galan P, Preziosi P, et al. The SU.VI.MAX Study: a randomized, placebo-controlled trial of the health effects of antioxidant vitamins and minerals. Arch Intern Med. 2004; 164:2335–42.
Lonn E, Bosch J, Yusuf S, et al. Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial. JAMA. 2005; 293:1338–47
Lee IM, Cook NR, Gaziano JM, et al. Vitamin E in the primary prevention of cardiovascular disease and cancer: the Women’s Health Study: a randomized controlled trial. JAMA. 2005; 294:56–65
Cook NR, Albert CM, Gaziano JM, et al. A randomized factorial trial of vitamins C and E and beta carotene in the secondary prevention of cardiovascular events in women: results from the Women’s Antioxidant Cardiovascular Study. Arch Intern Med 2007; 167:1610–1618.
Grodstein F, Kang JH, Glynn RJ, Cook NR, Gaziano JM. A randomized trial of beta-carotene supplementation and cognitive function in men: the Physicians’ Health Study II. Arch Intern Med. 2007; 167:2184–90.
Bartlett HE, Eperjesi F. Effect of lutein and antioxidant dietary supplementation on contrast sensitivity in age-related macular disease: a randomized controlled trial. Eur J Clin Nutr. 2007; 61:1121-27
Hercberg S, Ezzedine K, Guinot C, et al. Antioxidant supplementation increases the risk of skin cancers in women but not in men. J Nutr. 2007; 137:2098-105
Sesso HD, Buring JE, Christen WG, et al. Vitamins E and C in the prevention of cardiovascular disease in men: the Physicians’ Health Study II randomized controlled trial. JAMA. 2008; 300:2123–2133
Lippman SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers. JAMA. 2009; 301:39–51
Song Y, Cook NR, Albert CM, et al. Effects of vitamins C and E and beta-carotene on the risk of type 2 diabetes in women at high risk of cardiovascular disease: a randomized controlled trial. Am J Clin Nutr.2009; 90:429–437.
Lin J, Cook NR, Albert C, et al. Vitamins C and E and beta carotene supplementation and cancer risk: a randomized controlled trial. Je National Cancer Institute. 2009; 101:14–23
Gaziano JM, Glynn RJ, Christen WG, et al. Vitamins E and C in the prevention of prostate and total cancer in men: the Physicians’ Health Study II randomized controlled trial. JAMA. 2009; 301:52–62
Christen WG, Glynn RJ, Sesso HD, et al. Age-related cataract in a randomized trial of vitamins E and C in men. Arch Ophthalmol.2010; 128:1397–1405.
Crowe FL, Roddam AW, Key TJ, et al. Fruit and vegetable intake and mortality from ischaemic heart disease: results from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Heart Study. Eur Heart J. 2011; 32:1235–1243
Goodman M, Bostick RM, Kucuk O, et al. Clinical trials of antioxidants as cancer prevention agents: past, present, and future. Free Rad Biol Med 2011; 51:1068–1084.
Jerome-Morais A, Diamond AM, Wright ME. Dietary supplements and human health: for better or for worse? Mol Nutr & Food Res.2011; 55:122–135.
Klein EA, Thompson IM Jr, Tangen CM, et al. Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2011; 306:1549–1556
Dysken MW, Sano M, Asthana S, et al. Effect of Vitamin E and Memantine on Functional Decline in Alzheimer Disease: The TEAM-AD VA Cooperative Randomized Trial. JAMA. 2014; 311:33-44
Marrocco I, Altieri F, Peluso I. Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans. Oxid Med Cell Longev 2017; 2017:6501046. doi: 10.1155/2017/6501046. Epub 2017 Jun 18.
Egea J, Fabregat I, Frapart YM, Ghezzi P, Görlach A, et al for the COST Action BM1203 (EU-ROS) consortium. European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS). Redox Biol 2017; 13:94-162.
Höhn A, Weber D, Jung T, Ott C, Hugo M, Kochlik B, Kehm R, König J, Grune T, Castro JP. Happily (n)ever after: Aging in the context of oxidative stress, proteostasis loss and cellular senescence. Redox Biol. 2017; 11:482-501