We often heard about ‘antioxidants’ and ‘free radicals’. These terms are inarguably no stranger to health enthusiasts who constantly look for health food and supplements to promote general health. However, some people are only familiar with the terms but not quite sure about what they really are and most importantly – how it works.
Here, we are putting together the basics of antioxidants and free radicals backed by science and clinical research as well as food ingredients that are packed with antioxidants.
What is free radical?
Our body cells use oxygen to generate energy. This process yielded a natural by-product, namely free radicals. As a result of normal cellular metabolism, free radicals are not entirely a ‘bad thing’. When present in small amounts, free radicals exert beneficial effects on cellular responses and immune function. However, when present in high concentration, free radicals tend to be unstable and highly reactive which lead to oxidative stress (a condition which makes a significant contribution in ageing, cancers, inflammation, atherosclerosis, high blood pressure, diabetes and many others).1-3
Apart from being an inevitable outcome of normal metabolic process, free radicals can be derived from external sources such as exposure to radiation, air pollution, cigarette smoke, alcohol, certain drugs, heavy metals and industrial chemicals.
What is antioxidant?
An antioxidant is a molecule acts to counterbalance the effects of overloaded free radicals in one of two main ways. First, antioxidants break the chain reaction until a free radical formed is stabilized or until it turns into an inoffensive product. The other way is preventing the formation of free radicals before it can initiate a chain reaction by scavenging the free radicals.1
Similar to free radicals, many antioxidants are produced in the body such as glutathione, coenzyme Q10, melatonin, uric acid, etc. While for antioxidants which cannot be produced by the body and need to be obtained through foods and supplements (also known as dietary antioxidants) are vitamin C, vitamin E, carotenoids, trace metals (selenium, manganese, zinc), flavonoids, omega 3 and omega 6 fatty acids. It is believed that numerous chronic and degenerative illnesses are closely associated to deficiency of dietary antioxidants.1
The other source of antioxidants
It is not surprising to see that many food and plant-based ingredients are packed with antioxidants. Apart from the above-mentioned antioxidants, take a glance on the other 10 ingredients that are in our Top 10’s list.
Grape seed has always been on the top list when comes to plant-based antioxidant supplements. It was found that grape seed possesses the highest antioxidant capacity, followed by the grape skin and then the flesh.4 Flavonoids found in grape seed are the key compounds that exert an antioxidative property.
One of the most widely studied flavonoids found in grape seed, proanthocyanidin has shown to inhibit the generation of oxidized LDL (low-density lipoproteins, often referred as ‘bad’ cholesterol) in blood vessel walls that may contribute to arteriosclerosis.5 Another study conducted on 40 female volleyball players in Iran concluded that supplementation with grape seed extract for 8 weeks had beneficial effects on some biomarkers of oxidative stress and insulin parameters.6
Royal jelly is a white or yellowish substance secreted from the glands of worker honeybees. It is a food for young bees for the first 3 days of their lives and continues to become the sole food for queen bees.7 The prominent constituents found in royal jelly such as fatty acids, unique proteins and flavonoids have made it a promising antioxidant supplement for supporting healthy ageing.
A study conducted on 46 type 2 diabetic patients aged 25-65 years noted a decreased homeostasis model assessment for insulin resistance (HOMA-IR) and increased total antioxidant capacity in royal jelly supplemented group.8 Another latest article published in 2019 supported the intake of royal jelly for 8 weeks showed an increase in total antioxidant capacity in overweight adults. The same study also demonstrated a positive effect on subjects’ cholesterol profile, satiety, negative mood and inflammation.9
Spirulina is a type of blue-green algae naturally grows in high-salt alkaline water reservoirs in countries such as America, Mexico, Asia and Central Africa.10 It is rich in vitamins, minerals, protein, carotenoids, phycocyanins, essential fatty acids and other bioactive molecules. Several studies reported the beneficial effects of supplementing spirulina in protecting against oxidative damage.
One of the human studies conducted on type II diabetic patients suggested spirulina as a promising functional food for diabetes management due to the favourable results in antioxidant capacity and lowering effect on triglyceride concentration.11 The same positive outcome was also demonstrated in another study involved 78 healthy elderly aged around 60 – 87 years.12
Native to Asia and Africa, moringa is a plant best known for having a remarkable range of medical uses throughout the world. Various parts of the plant such as the leaves, fruit, roots and seeds have been long studied in the past due to the presence of both macro- and micronutrients as well as natural antioxidant molecules.13
The plant has reported being effective in improving the lipid profile and blood glucose level of type II diabetic patients by increasing the HDL (‘good’ cholesterol), lowering the LDL (‘bad’ cholesterol) and fasting blood glucose levels.14,15 In another human study shown that supplementing moringa leaf powder among postmenopausal women successfully improved the antioxidant capacity and blood glucose levels.16
Unlike other ingredients mentioned here, alpha lipoic acid (ALA) is neither food nor plant. It is an organosulfur compound produced from plants, animals, humans and exists in nature. As a strong antioxidant, it serves several roles in our body systems, namely acting as a free radical scavenger, removes heavy metals from the bloodstream and helps to regenerate other antioxidants such as glutathione, vitamin C and vitamin E internally.17 Obtain ALA from diet and supplementation is important due to human body only able to produce it in a low amount which is hardly enough to fulfil the energy requirement of the cell.17
Effects of ALA on diabetes-related neuropathy have been supported by numerous clinical studies. One of the studies suggested that type II diabetic patients with symptomatic polyneuropathy responded well with improvement in neuropathic symptoms to the administration of ALA mainly through reducing oxidative stress.18
Generally known as wolfberry, it is a bright orange-red berry with a sweet and tangy flavour and regarded as a functional food in many Asian countries. The bioactive compounds found in goji berries such as polysaccharide, carotenoids (zeaxanthin) and flavonoids possess a high antioxidant capacity.
By inhibiting the production of free radicals and increasing the functional abilities of antioxidants, polysaccharides in goji berry help to alleviate dry eye symptoms.19 Another study also confirmed the beneficial effect on macular health of elderly subjects with the increase in plasma zeaxanthin and antioxidant levels after supplementation with goji berry for 90 days.20
Many people often linked cranberry products to alternative remedy for urinary tract infection (UTI). Numbers of scientific evidence proposed stated that the active compounds in cranberry interfere the bacteria adhesion to the urinary tract and thereby protect against infection.21 Also, cranberry is particularly high in bioactive constituents such as proanthocyanidins, anthocyanidins and phenolic acids which contributed to antioxidant properties.
Both human and animal studies found that consumption of cranberry juice/powder increased antioxidant capacity and significantly reduced lipid oxidation which is favourable in preventing cardiovascular health issue.22-24
The date palm tree is one of the oldest cultivated plants of humankind. The fruit of the plant – dates are widely used as staple food in the Middle East, Africa and Southeast Asia countries.25 Dates are berry with a sweet flavour and provide excellent nutritional values. Numbers of medicinal properties have been demonstrated for dates such as antioxidant activity, anti-inflammatory activity, antitumor effect, neuroprotective effect and many others.
A recent study was conducted to evaluate the antioxidant, anti-inflammatory, and the antitumoral effects of dates shown a favourable result due to the high content of phytochemical compounds and its high free radical scavenging capacities.26 Besides, ferulic acid and protocatechuic acid are phenolic compounds found to reduce the oxidative damage that leads to degeneration of nervous system such as Alzheimer’s disease.27
Lycopene, the red pigment that gives the tomato its bright red colour is a predominant carotenoid found in tomatoes and tomato products. It is a more potent antioxidant than α or β-carotene.28
Besides lycopene, tomatoes do contain other carotenoids such as phytoene, phytofluene and β-carotene. A study conducted on healthy men and women found that even a low intake of carotenoids from tomato products is sufficed to observe the improvement in cellular antioxidant protection.29 Some products containing lycopene have been marketed as a health supplement for men which is mainly due to numerous promising evidence of the capability of lycopene in fighting against oxidative stress-related infertility and reducing prostate cancer risk.30,31
Turmeric is a vibrant yellow spice derived from the rhizome of the plant. It has a long history of use in traditional medicines and cookery in China and India.32 In recent years, turmeric has become one of the most popular ingredients. The active constituent in turmeric, namely curcumin has been extensively studied for its antioxidative and anti-inflammatory effects.
Lipid peroxidation is the main cause of many cardiovascular diseases. Curcumin acts as a free radical scavenger is effective in increasing levels of antioxidant and reducing malondialdehyde (MDA) level, a well-known end product of lipid peroxidation.33 Hence, curcumin supplementation is useful for prevention and reducing the risks of atherosclerosis.34 The same positive result was also reported in a study involved 22 healthy and active male participants whereby one-week oral supplementation of curcumin increased antioxidant capacity and alleviated markers of oxidative stress following an intensive endurance-like exercise.35
- Pham-Huy LA, He H, Pham-Huy C. Free radicals, antioxidants in disease and heath. Internation Journal of Biomedical Science. 2008;4(2):89-96.
- Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: impact on human health. Pharmacogn Rev. 2010;4(8):118-126.
- Birben E, Sahiner UM, Sackesen C, Erzurum S, Kalayci O. Oxidative stress and antioxidant defense. World Allergy Organization. 2012;5:9-19.
- Xia EQ, Deng GF, Guo YJ, Li HB. Biological activities of polyphenols from grapes. International Journal of Molecular Sciences. 2010;11:622-646.
- Sano A, Uchida R, Saito M, Shioya N, Komori Y, Tho Y, et al. Beneficial effects of grape seed extract on malondialdehyde-modified LDL. J. Nutr. Sci. Vitaminol. 2007;53:174-182.
- Taghizadeh M, Malekian E, Memarzadeh MR, Mohammadi AA, Asemi Z. Grape seed extract supplementation and the effects on the biomarkers of oxidative stress and metabolic profiles in female volleyball players: a randomized, double-blind, placebo-controlled clinical trial. Iranian Red Crescent Medical Journal. 2016;18(9):e31314.
- Kunugi H, Ali AM. Royal jelly and its components promote healthy aging and longevity: from animal models to humans. International Journal of Molecular Science. 2019;20(4662):1-26.
- Shidfar F, Jazayeri S, Mousavi SN, Malek M, Hosseini AF, Khoshpey B. Does supplementation with royal jelly improve oxidative stress and insulin resistance in type 2 diabetic patients?. Iran J. Public Health. 2015;44(6):797-803.
- Petelin A, Kenig S, Kopinc R, Dezelak M, Bizjak MC, Praznikar ZJ. Effects of royal jelly administration on lipid profile, satiety, inflammation, and antioxidant capacity in asymptomatic overweight adults. Evidence-Based Complementary and Alternative Medicine. 2019; https://doi.org/10.1155/2019/4969720.
- Deng R, Chow TJ. Hypolipidemic, antioxidant and anti-inflammatory activities of microalgae spirulina. Cardiovasc. Ther. 2010;28(4):e33–e45. doi:10.1111/j.1755-5922.2010.00200.x.
- Lee EH, Park JE, Choi YJ, Huh KB, Kim WY. A randomized study to establish the effects of spirulina in type 2 diabetes mellitus patients. Nutrition Research and Practice. 2008;2(4):295-300.
- Park HJ, Lee YJ, Ryu HK, Kim MH, Chung HW, Kim WY. A randomized double-blind, placebo-controlled study to establish the effects of spirulina in elderly Koreans. Ann. Nutr. Metab. 2008;52(4):322-328.
- Luqman S, Srivastava S, Kumar R, Maurya AK, Chanda D. Experimental assessment of moringa oleifera leaf and fruits for its antistress, antioxidant, and scavenging potential using in vitro and in vivo Evidence-Based Complementary and Alternative Medicine. 2012; doi:10.1155/2012/519084.
- Kumari J. Hypoglycaemic effect of moringa oleifera and azadirachta indica in type 2 diabetes mellitus. An International Quartery Journal of Life Sciences. 2010;5(2):211-214.
- Nambiar, VS. Guin P, Parnami S, Daniel M. Impact of antioxidants from drumstick leaves on the lipid profile of hyperlipidemics. Journal of Herbal Medicine and Toxicology. 2010;4(1):165-172.
- Kushwaha S, Chawla P, Kochhar A. Effect of supplementation of drumstick (moringa oleifera) and amaranth (amaranthus tricolor) leaves powder on antioxidant profile and oxidative status among postmenopausal women. Journal of Food Science and Technology. 2014;51:3464-3469.
- Salehi B, Yilmaz YB, Antika G, Tumer TB, Mahomoodally MF, Lobine D, et al. Insights on the use of α-lipoic acid for therapeutic purposes. Biomolecules. 2019;9(356): doi:10.3390/
- Garcia-Alcala H, Santos Vichido CI, Macedo SI, Genestier-Tamborero CN, Minutti-Palacios M, Tamez OH, et al. Treatment with α-lipoic acid over 16 weeks in type 2 diabetic patients with symptomatic polyneuropathy who responded to initial 4-week high-dose loading. Journal of Diabetes Research. 2015; http://dx.doi.org/10.1155/2015/189857.
- Chien KJ, Horng CT, Huang YS, Hsieh YH, Wang CJ, Yang JS, et al. Effects of lyceum barbarum (goji berry) on dry eye disease in rats. Molecular Medicine Reports. 2018;17:809-818.
- Bucheli P, Vidal K, Shen L, Gu Z, Zhang C, Miller LE, et al. Goji berry effects on macular characteristics and plasma antioxidant levels. Optom. Vis. Sci. 2011;88(2):257-262.
- Blumberg JB, Camesano TA, Cassidy A, Kris-Etherton P, Howell A, Manach C, et al. Cranberries and their bioactive constituents in human health. Adv. Nutr. 2013;4:618-632.
- Pedersen CB, Kyle J, Jenkinson AMcE, Gardner PT, McPhail DB, Duthie GG. Effects of blueberry and cranberry juice consumption on the plasma antioxidant capacity of healthy female volunteers. European Journal of Clinical Nutrition. 2000;54:405-408.
- Basu A, Betts NM, Ortiz J, Simmons B, Wu MY, Lyons TJ. Low-calorie cranberry juice decreases lipid oxidation and increases plasma antioxidant capacity in women with metabolic syndrome. Nutr. Res. 2011;31(3):190-196.
- Kim MJ, Kim JH, Kwak HK. Antioxidant effects of cranberry powder in lipopolysaccharide treated hyperchlolesterolemic rats. Prev. Nutr. Food Sci. 2014;19(2):75-81.
- Rahmani AH, Aly SM, Ali H, Babiker AY, Srikar S, Khan AA. Therapeutic effects of date fruits (phoenix dactylifera) in the prevention of diseases via modulation of anti-inflammatory, anti-oxidant and anti-tumour activity. Int. J. Clin. Exp. Med. 2014;7(3):483-491.
- Abed HE, Chakroun M, Koubaa ZA, Drira N, Marrakchi N, Mejdoub H. Antioxidant, anti-inflammatory, and antitumoral effects of aqueous ethanolic extract from phoenix dactylifera l. parthenocarpic dates. BioMed Research International. 2018; https://doi.org/10.1155/2018/1542602.
- Subash S, Essa MM, Braidy N, Awlad-Thani K, Vaishnav R, Al-Adawi S. Diet rich in date palm fruits improves memory, learning and reduces beta amyloid in transgenic mouse model of Alzheimer’s disease. Journal of Ayurveda & Integrative Medicine. 2015;6(2):111-120.
- Di Mascio P, Kaiser S, Sies H. Lycopene as the most efficient biological carotenoid singlet oxygen quencher. Arch. Biochem. Biophys. 1989;274(2):532-538.
- Porrini M, Riso P, Brusamolino A, Berti C, Guarnieri S, Visioli F. Daily intake of a formulated tomato drink affects carotenoid plasma and lymphocyte concentrations and improves cellular antioxidant protection. British Journal of Nutrition. 2005;93:93-99.
- Gann PH, Ma J, Giovannucci E, Willett W, Sacks FM, Hennekens CH. Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis. Cancer Research. 1999;59:1225-1230.
- Hekimoglu A, Kurcer Z, Aral F, Baba F, Sahna, Atessahin A. Lycopene, an antioxidant carotenoid, attenuates testicular injury caused by ischemia/reperfusion in rats. J. Exp. Med. 2009;218:141-147.
- Hatcher H, Planalp R, Cho J, Torti FM, Torti SV. Curcumin: from ancient medicine to current clinical trials. Cell. Mol. Life Sci. 2008;65:1631-1652.
- Alizadeh M, Kheirouri S. Curcumin reduces malondialdehyde and improves antioxidants in humans with diseased conditions: a comprehensive meta-analysis of randomized controlled trials. BioMedicine. 2019;9(4):10-22.
- Bosca AR, Carrion Gutierrez MA, Soler A, Puerta C, Diez A, Quintanilla E. Effects of the antioxidant turmeric on lipoprotein peroxides: implications for the prevention of the atherosclerosis. Age. 1997;20:165-168.
- Roohi BN, Moradlou AN, Bolboli L. Influence of curcumin supplementation on exercise-induced oxidative stress. Asian J. Sports Med. 2017;8(1):e35776.