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Oxidative stress and Nutrition

The human body constantly produces τthe so-called free radicals during its metabolic processes.

Free radicals derived from oxygen are called free oxygen radicals (ROS-reactive oxygen species) and have one or more unbound electrons in their outer shell, as a result, they are extremely unstable and reactive.


Free radicals can easily oxidize proteins, unsaturated fatty acids and DNA causing damage so they have been linked to diseases such as cancer, infertility, neurodegenerative diseases, aging and other.

On the other hand, in small concentrations, they not only do not cause damage, but are considered necessary and useful for the body because they affect the regulation and completion of biochemical processes and are considered necessary for cell growth, the immune response against infections, embryogenesis, sperm maturation and are also necessary in the process of myocyte regeneration and muscle hypertrophy after training.


For free radicals, which in certain concentrations can become extremely harmful, the body has provided with two antioxidant systems which protect it. One of the systems refers to enzymatic antioxidants, which are endogenous, such as superoxide dismutase (SOD), catalase, and glutathione peroxidase. The second system includes non-enzymatic antioxidants, which are basically vitamins and trace elements that the body supplies mainly through food. Vitamin C (L-ascorbic acid), tocopherol or otherwise vitamin E, glutathione, various flavonoids and phenolic compounds, zinc, selenium and others belong to this category of antioxidants. With these mechanisms, the body achieves the balance of oxidation (redox), however, some exogenous factors have the ability to affect this balance and cause oxidative stress. Such as:

  • Alcohol

  • Smoking

  • Radiation

  • Obesity

  • Exercise (the free radicals that come from exercise have, in addition to negative, positive effects. Exercise increases antioxidant activities in skeletal muscle, heart, and liver and strengthens the antioxidant defense system)


Nutrition:

Antioxidant supplements: excessive consumption of antioxidants has opposite effects than expected.

Examples:

  • Vitamin E despite its antioxidant effect, it is confirmed that higher doses of it in the body are toxic.

  • Vitamin A: as an antioxidant has an inhibitory effect on cancer, however, it seems to act in exactly the opposite way in smokers.

  • Vitamin C: in low concentrations was found to be associated with oxidative stress and DNA damage, but it causes the same effects when found in high concentrations.

These examples fully explain the so-called “antioxidant paradox”


The human body derives non-enzymatic antioxidants mainly from food.
  • Vitamin C or ascorbic acid: citrus fruits and vegetables such as tomato and potato

  • vitamin E: olive oil, leafy vegetables (e.g. spinach) and nuts.

  • Antioxidants are also present in meat and dairy products such as carnitine and coenzyme Q10 which is found in meat, fish and whole grain products.

  • Polyphenols: antioxidant and anti-inflammatory properties with the result that they act positively against diseases such as cancer. Curcumin, resveratrol, catechins (e.g. epigallocatechin) etc.

  • Zinc: trace element found in red meat, poultry and oysters.

  • Selenium: seafood, nuts, meat and dairy products.

  • Folic acid: leafy vegetables, nuts, beans, dairy products, meat and eggs.


Conclusion: oxygen free radicals (ROS) have confirmed positive and negative effects depending on their concentration. The body itself has mechanisms to fight free radicals and achieve the required balance. In cases of disturbance of this balance for any reason, in addition to the antioxidants that humans get from food every day, it may be recommended to take antioxidant supplements. Special attention is needed here, because larger doses of antioxidants are most often harmful to the body (antioxidant paradox). A balanced diet covers the need for antioxidants and only in exceptional cases may additional exogenous intake be needed.

Bibliography:

  • Forman HJ, Zhang H. Targeting oxidative stress in disease: promise and limitations of antioxidant therapy. Nat Rev Drug Discov. 2021 Sep;20(9):689-709. doi: 10.1038/s41573-021-00233-1. Epub 2021 Jun 30. Erratum in: Nat Rev Drug Discov. 2021 Aug;20(8):652. PMID: 34194012; PMCID: PMC8243062.

  • Teleanu DM, Niculescu AG, Lungu II, Radu CI, Vladâcenco O, Roza E, Costăchescu B, Grumezescu AM, Teleanu RI. An Overview of Oxidative Stress, Neuroinflammation, and Neurodegenerative Diseases. Int J Mol Sci. 2022 May 25;23(11):5938. doi: 10.3390/ijms23115938. PMID: 35682615; PMCID: PMC9180653.

  • Cory, H. et al. (2018) ‘The Role of Polyphenols in Human Health and Food Systems: A Mini-Review’, Frontiers in Nutrition, 5(September), pp. 1–9. doi: 10.3389/fnut.2018.00087.

  • Henkel, R., Sandhu, I. S. and Agarwal, A. (2018) ‘The excessive use of antioxidant therapy: A possible cause of male infertility?’, Andrologia, (September), p. e13162. doi: 10.1111/and.13162.

  • Kawamura, T. and Muraoka, I. (2018) ‘Exercise-Induced Oxidative Stress and the Effects of Antioxidant Intake from a Physiological Viewpoint’, Antioxidants, 7(9), p. 119. doi: 10.3390/antiox7090119.

  • Sir Elkhatim, K. A., Elagib, R. A. A. and Hassan, A. B. (2018) ‘Content of phenolic compounds and vitamin C and antioxidant activity in wasted parts of Sudanese citrus fruits’, Food Science & Nutrition, 6(5), pp. 1214–1219. doi: 10.1002/fsn3.660.


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