Essential Nutrients: Antioxidants

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One of the fundamentals of healthy living.

It is well known that regular consumption of a diet rich in plants such as fruits, vegetables and grains is an important part of a healthy lifestyle.[3] One of the reasons for this is because plant sources are rich in antioxidants. Spices, herbs and supplements are the richest source of antioxidants, but berries, fruits, vegetables and their products also have high antioxidant values.[2] Even chocolate and coffee have some antioxidant properties! The knowledge around antioxidants dates back to the late 19th Century, and they have long been featured in many health blogs and supplement brands across the internet, due to the claims about their health benefits. So is there any substance to these claims, and can antioxidants improve any specific conditions, or just general health? 

What are Antioxidants?

The function of antioxidants is to reduce oxidative stress within the body. Oxidative stress is a state of imbalance between oxidants (oxygen and nitrogen molecules that react inside your body) and antioxidants in favour of the oxidants, which leads to damaging effects.[8] Overproduction of oxidants can damage large biomolecules such as lipids, DNA, and proteins, in particular.[1] The majority of antioxidant activity in plant sources comes from phytochemicals, but fruits and vegetables contain many different compounds that have antioxidant properties (such as vitamin C and vitamin E, whose activities have been established in recent years).[1,5] Phytochemicals are compounds produced and used by plants as their chemical defence against natural enemies. When consumed as food they are recognised as key components for preventing human diseases and maintaining good health.[2] The major antioxidant phytochemicals in plants are carotenoids, phenolic compounds and glucosinolates.[3] Polyphenols and carotenoids are the two main kinds of antioxidant phytochemicals, and they contribute the most to the antioxidant properties of foods/plants.[1] So what exactly are all these phytochemicals? To start, carotenoids are a group of natural pigments that are synthesized by plants and microorganisms.[2] They are responsible for the yellow, orange and red colours of many plants and act as photosensitisers in the photosynthesis of plants. They also help protect against photo-damage in plants. Phenolic compounds prevent fatty acids from oxidative decay and provide a defence against oxidative stress from oxidising agents and free radicals.[3] Free radicals are molecules within the body that have one unpaired electron, and they cause damage by trying to take electrons from other molecules. This is why it’s important that antioxidants scavenge for them and combat the damage they do. Phenolic compounds can be either flavonoids or non-flavonoids, depending on the number and arrangement of their carbon atoms.[3] Lastly, glucosinolates are a group of sulphur and nitrogen-containing compounds in plant species such as mustard and broccoli.[4] They are plants’ protectants against herbivores and stress.[4] 

Health Benefits

What are some of the benefits of antioxidants then? Recent studies have found that overproduction of oxidants in the human body can be responsible for the pathogenesis of some chronic diseases.[1] Since antioxidants reduce oxidants and their damaging effects, it wouldn't be outlandish to think that antioxidants could have a hand in protecting against some chronic diseases, because of the role of oxidants in creating them. As a result of that line of thinking, it has been demonstrated in some studies that fruits, vegetables and grains exert a protective effect against the development of chronic diseases such as cardiovascular diseases (CVD), diabetes and cancers.[1] Additionally, inflammation, hypersensitivity, and autoimmune conditions may result when antioxidant, free radical scavenging systems get overwhelmed.[6] Thankfully, most antioxidant phytochemicals have been found to have anti-inflammatory action.[1] It's also been found that people who eat higher amounts of fruits and vegetables have reduced by about one-half the risk of cancer and have lower mortality rates.[3] Now that's a reason to increase your antioxidant intake, if any!

It’s been mentioned that antioxidants can improve cardiovascular disease (CVD). Let's take a further look at that. Oxidative stress has been recognised as a key mechanism in the development of vascular damage, so it is understandable that antioxidants could work against that.[9] It has been shown that antioxidant polyphenols could improve endothelial function, and therefore play an important role in the prevention of CVD, especially since there are links between vascular inflammation, endothelial dysfunction and oxidative stress.[1, 7]. Endothelial function describes the work of the thin membrane that lines the heart and the blood vessels.[11] It controls the relaxation and contraction of the vessels, and releases enzymes that control blood clotting and platelets, along with helping the immune system.[11] So it’s pretty important! Other studies have concluded that antioxidant phytochemicals could be good candidates for preventing and treating CVD through direct antioxidant activity alongside their other bioactivities (such as anti-inflammation).[1] This is especially encouraging, as cardiovascular diseases are the leading cause of death worldwide except in Africa.[10] As well as improving the symptoms of full cardiovascular disease, antioxidants could possibly help prevent it, as one study shows that the oxidant scavenging action of antioxidants is able to bring improvement in blood pressure which, if continuously high, is a factor in the development of cardiovascular disease.[7] 

Although the positive effects of antioxidants has been theorised and generally accepted for some time, the recent research into conditions that antioxidants can help is really promising. Chronic diseases (particularly cardiovascular diseases, cancers, and diabetes, as mentioned above) affect many people across the globe, and impact their lives quite negatively. So to find that antioxidants can have a positive effect on improving these conditions is quite reassuring, especially for those who prefer natural remedies. Additionally, the fact that antioxidants are readily available in so many plant sources and supplements (due to their popularity) means that it is quite easy to get all the antioxidants necessary not only for those with chronic conditions, but also for those wishing to improve their health or continue looking after their body. 

References

1) Zhang Y, Gan R, Li S, Zhou Y, Li A, Xu D et al. Antioxidant Phytochemicals for the Prevention and Treatment of Chronic Diseases. Molecules [Internet]. 2015 [cited 13 June 2021];20(12):21138-21156. Available from: https://www.mdpi.com/1420-3049/20/12/19753

2) Li H, Tsao R, Deng Z. Factors affecting the antioxidant potential and health benefits of plant foods. Canadian Journal of Plant Science [Internet]. 2012 [cited 13 June 2021];92(6):1101-1111. Available from: https://cdnsciencepub.com/doi/full/10.4141/cjps2011-239

3) Ford ES, Bergmann MM, Kröger J, Schienkiewitz A, Weikert C, Boeing H. Healthy living is the best revenge: findings from the European Prospective Investigation Into Cancer and Nutrition-Potsdam study. Archives of internal medicine. 2009 Aug 1;169(15):1355-62.

4) Hansen M, Bengtsson GB, Borge GI, Berge L, Wold AB. Red cabbage, a vegetable rich in health-related glucosinolates. InV International Symposium on Brassicas and XVI International Crucifer Genetics Workshop, Brassica 2008 867 2008 Sep 8 (pp. 61-66).

5) García-Alonso M. Evaluation of the antioxidant properties of fruits. Food Chemistry [Internet]. 2004 [cited 13 June 2021];84(1):13-18. Available from: https://www.sciencedirect.com/science/article/pii/S0308814603001602?casa_token=cWVkOL7OXIgAAAAA:diAZhcWjG9x_SLprYKn4nPyivgQsDb6QIUwnAkh8khHUQ7Xw6LUz5-66A6v4iS6Cg4ambNfF

6) Matés J, Pérez-Gómez C, De Castro I. Antioxidant enzymes and human diseases. Clinical Biochemistry [Internet]. 1999 [cited 13 June 2021];32(8):595-603. Available from: https://www.sciencedirect.com/science/article/pii/S0009912099000752?casa_token=oyjLn9EpWA8AAAAA:OsJ-9mvksJffAfFcebrQC55roW4a1EdgO1-Nj9OzZIZkXUzS0UDapJaHKJO0PXGHT-Ws1qNu

7) Siti H, Kamisah Y, Kamsiah J. The role of oxidative stress, antioxidants and vascular inflammation in cardiovascular disease (a review). Vascular Pharmacology [Internet]. 2015 [cited 13 June 2021];71:40-56. Available from: https://www.sciencedirect.com/science/article/pii/S1537189115000427?casa_token=i_wTa0_LMMEAAAAA:6YhCshoyyeBkc8GjsmEP-g0AanL2jRB4e4x9-IEBu1xq9LnJEWujr9rAk_5Uqv1vZZBAGQ-C

8) Sies H. Oxidative stress: oxidants and antioxidants. Experimental Physiology [Internet]. 1997 [cited 13 June 2021];82(2):291-295. Available from: https://physoc.onlinelibrary.wiley.com/doi/abs/10.1113/expphysiol.1997.sp004024)

9) Minuz P, Fava C, Cominacini L. Oxidative stress, antioxidants, and vascular damage. British Journal of Clinical Pharmacology [Internet]. 2006 [cited 13 June 2021];61(6):774-777. Available from: https://bpspubs.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2125.2006.02681.x

10) Mendis S, Puska P, Norrving B. Global Atlas on Cardiovascular Disease Prevention and Control [Internet]. World Health Organization in collaboration with the World Heart Federation and the World Stroke Organization.; 2011 [cited 14 June 2021]. Available from: https://web.archive.org/web/20140817123106/http://whqlibdoc.who.int/publications/2011/9789241564373_eng.pdf?ua=1

11) Endothelial Function Testing | Cedars-Sinai [Internet]. Cedars-sinai.org. 2021 [cited 15 June 2021]. Available from: https://www.cedars-sinai.org/programs/heart/clinical/womens-heart/services/endothelial-function-testing.html

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