Antioxidant

    From Longevity Wiki

    Antioxidants are compounds that can prevent or slow down the oxidation of other molecules. Oxidation is a chemical reaction that can produce free radicals, leading to chain reactions that may damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates and inhibiting other oxidation reactions. They do this by being oxidized themselves, making them crucial in the body's defense against oxidative stress.[1]

    Known dietary antioxidants are vitamins A, C, and E, but the term antioxidant has also been applied to numerous other dietary compounds that only have antioxidant properties in vitro, with little evidence for antioxidant properties in vivo.[2] Dietary supplements marketed as antioxidants have not been shown to maintain health or prevent disease in humans.[2]

    Types of Antioxidants

    There are several types of antioxidants, each playing a distinct role in combating oxidative stress:

    • Enzymatic Antioxidants: These include enzymes such as superoxide dismutase (SOD), catalase, and glutathione peroxidase, which directly neutralize ROS.
    • Non-enzymatic Antioxidants: This group includes Vitamin C, Vitamin E, and glutathione. These small molecule antioxidants scavenge free radicals and contribute to the repair and regeneration of oxidized antioxidants.
    • Metal-Binding Proteins: Proteins such as ferritin and ceruloplasmin that sequester free iron and copper ions, which can catalyze the production of free radicals, thus reducing oxidative stress.

    Dietary Sources of Antioxidants

    Diet is a significant source of antioxidants. Foods high in antioxidants include:

    • Fruits and Vegetables: Berries, citrus fruits, and leafy greens are high in vitamins C and E, as well as various phytochemicals.
    • Nuts and Seeds: These are sources of vitamin E and selenium, another important antioxidant.
    • Whole Grains: Whole grains contain antioxidants like vitamin E and phytochemicals.
    • Tea and Coffee: Rich in flavonoids, these beverages contribute significantly to the total antioxidant intake.

    Antioxidant Supplements

    Antioxidant supplements have gained popularity as potential aids in combating oxidative stress and its related aging processes. These supplements are concentrated forms of antioxidants that can be taken in addition to a regular diet. However, antioxidant supplements have not shown preventive effects and may be harmful with unwanted consequences to our health. The optimal source of antioxidants seems to come from our diet, not from antioxidant supplements.[3]

    Older observational studies and some randomized clinical trials with high risks of systematic errors ('bias') have suggested that antioxidant supplements may improve health and prolong life. A number of randomized clinical trials with adequate methodologies observed neutral or negative results of antioxidant supplements. Recently completed large randomized clinical trials with low risks of bias and systematic reviews of randomized clinical trials taking systematic errors ('bias') and risks of random errors ('play of chance') into account have shown that antioxidant supplements do not seem to prevent cancer, cardiovascular diseases, or death. Even more, beta-carotene, vitamin A, and vitamin E may increase mortality.[4] Some recent large observational studies now support these findings. According to recent dietary guidelines, there is no evidence to support the use of antioxidant supplements in the primary prevention of chronic diseases or mortality.[5][3]

    List of Antioxidant Supplements

    Here's a list of some widely used antioxidant supplements:

    • Vitamin C (Ascorbic Acid): A water-soluble vitamin known for its role in boosting the immune system and scavenging free radicals.
    • Vitamin E (Tocopherol): A fat-soluble vitamin that protects cell membranes from oxidative damage, especially in lipid-rich areas of the body.
    • Beta-Carotene: A precursor to vitamin A and a powerful antioxidant, particularly effective against singlet oxygen.
    • Selenium: A trace mineral that is a component of antioxidant enzymes like glutathione peroxidase.
    • Zinc: Essential for the functioning of several antioxidant enzymes and immune function.
    • Coenzyme Q10 (CoQ10): An important molecule in energy production and also acts as an antioxidant in cell membranes and lipoproteins.
    • Flavonoids: A diverse group of phytonutrients found in many fruits and vegetables, known for their antioxidant properties.
    • Lycopene: A carotenoid found in tomatoes, watermelon, and other red fruits and vegetables, known for its antioxidant capacity.
    • Resveratrol: Found in the skin of red grapes, berries, and peanuts, resveratrol is studied for its antioxidant and anti-aging properties.
    • Curcumin: The active ingredient in turmeric, curcumin possesses strong antioxidant and anti-inflammatory properties.
    • Alpha-Lipoic Acid: A compound that works with mitochondria and the body's natural antioxidant defenses.
    • Green Tea Extract: Rich in catechins, green tea extract is renowned for its antioxidant properties.

    Antioxidant Stress

    Main article: Oxidative Stress § Antioxidative Stress

    The concept of antioxidative stress may best be described by excessive or detrimental nutritional consumption of a diet rich in antioxidants, unbalancing the immune systems' pathogenic response processes. Serious health conditions can result if these processes are chronically unbalanced, ranging from acute to chronic. Immunological stress by over-supplementation of antioxidants facilitates adverse health effects specifically including allergies, asthma, and physiological alterations (especially of the skin).

    Oxygen Radical Absorbance Capacity (ORAC)

    Measurement of polyphenol and carotenoid content in food is not a straightforward process, as antioxidants collectively are a diverse group of compounds with different reactivities to various reactive oxygen species. In food science analyses in vitro, the oxygen radical absorbance capacity (ORAC) was once an industry standard for estimating antioxidant strength of whole foods, juices and food additives, mainly from the presence of polyphenols.[6][7] Earlier measurements and ratings by the United States Department of Agriculture were withdrawn in 2012 as biologically irrelevant to human health, referring to an absence of physiological evidence for polyphenols having antioxidant properties in vivo.[8] Consequently, the ORAC method, derived only from in vitro experiments, is no longer considered relevant to human diets or biology, as of 2010.[8]

    Legal

    Other than for dietary antioxidant vitamins—vitamin A, vitamin C and vitamin E—no food compounds have been proved with antioxidant efficacy in vivo. Accordingly, regulatory agencies such as the Food and Drug Administration of the United States and the European Food Safety Authority (EFSA) have published guidance forbidding food product labels to claim or imply an antioxidant benefit when no such physiological evidence exists.[9][10] This guidance for the United States and European Union establishes it is illegal to imply potential health benefits on package labels of products with high ORAC.

    See Also

    References

    1. Sies H et al.: Oxidative Stress. Annu Rev Biochem 2017. (PMID 28441057) [PubMed] [DOI]
    2. Jump up to: 2.0 2.1 Antioxidants: In Depth, https://www.nccih.nih.gov/health/antioxidants-in-depth
    3. Jump up to: 3.0 3.1 Bjelakovic G et al.: Antioxidant supplements and mortality. Curr Opin Clin Nutr Metab Care 2014. (PMID 24241129) [PubMed] [DOI]
    4. Bjelakovic G et al.: Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA 2007. (PMID 17327526) [PubMed] [DOI]
    5. Bjelakovic G et al.: Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2012. (PMID 22419320) [PubMed] [DOI] [Full text]
    6. Cao G, Alessio HM, Cutler RG; "Oxygen-radical absorbance capacity assay for antioxidants" , https://zenodo.org/record/1258621 , https://doi.org/10.1016/0891-5849(93)90027-R
    7. Ou B, Hampsch-Woodill M, Prior RL; "Development and validation of an improved oxygen radical absorbance capacity assay using fluorescein as the fluorescent probe" , https://doi.org/10.1021/jf010586o
    8. Jump up to: 8.0 8.1 Withdrawn: Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 (2010), http://www.ars.usda.gov/services/docs.htm?docid=15866
    9. Guidance for Industry, Food Labeling; Nutrient Content Claims; Definition for "High Potency" and Definition for "Antioxidant" for Use in Nutrient Content Claims for Dietary Supplements and Conventional Foods U.S. Department of Health and Human Services, Food and Drug Administration, Center for Food Safety and Applied Nutrition, June 2008
    10. "Scientific Opinion on the substantiation of health claims related to various food(s)/food constituent(s) and protection of cells from premature aging, antioxidant activity, antioxidant content and antioxidant properties, and protection of DNA, proteins and lipids from oxidative damage pursuant to Article 13(1) of Regulation (EC) No 1924/20061" , http://www.efsa.europa.eu/en/efsajournal/pub/1489 , https://doi.org/10.2903/j.efsa.2010.1489