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Updated: Oct 31, 2020

What are antioxidants?

Antioxidants are molecules that fight free radicals in your body.

Understanding Free radicals

Free radicals are unstable molecules in your body that can damage DNA, cell membranes and other parts of the cell.

The reason why they can cause disaster is because they have an unstable number of electrons. The instability causes them to rip off electrons from other molecules, damaging them in the process. Free radicals thus adversely alter lipids, proteins, and DNA and trigger a number of human diseases.

Free radicals and other ROS (Reactive Oxygen Species) are derived either from normal essential metabolic processes in the human body or from external sources such as exposure to X-rays, ozone, cigarette smoking, air pollutants, and industrial chemicals.

The most important oxygen-containing free radicals in many disease states are hydroxyl radical, superoxide anion radical, hydrogen peroxide, oxygen singlet, hypochlorite, nitric oxide radical, and peroxynitrite radical.

Oxidative Stress

This is the term used to describe an imbalance between free radical production and antioxidant defenses.

The initiation, promotion, and progression of cancer, as well as the side-effects of radiation and chemotherapy, have been linked to the imbalance between ROS and the antioxidant defense system. ROS have been implicated in the induction and complications of diabetes mellitus, age-related eye disease, and neurodegenerative diseases such as Parkinson's disease.


Antioxidants neutralise free radicals by giving up some of their own electrons. In making this sacrifice, they act as a natural "off" switch for the free radicals. This helps break a chain reaction that can affect other molecules in the cell and other cells in the body. But it is important to recognise that the term "antioxidant" reflects a chemical property rather than a specific nutritional property.

Our body's cells naturally produce some powerful antioxidants including glutathione, ubiquinol, and uric acid which are produced during normal metabolism in the body. The foods you eat supply other antioxidants, such as vitamins C and E. Plants are full of compounds known as phytochemicals—literally, "plant chemicals"—many of which seem to have antioxidant properties as well. For example, after vitamin C has "quenched" a free radical by donating electrons to it, a phytochemical called hesperetin (found in oranges and other citrus fruits) restores the vitamin C to its active antioxidant form. Carotenoids (such as lycopene in tomatoes and lutein in kale) and flavonoids (such as flavanols in cocoa, anthocyanins in blueberries, quercetin in apples and onions, and catechins in green tea) are also antioxidants.

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 wheatgerm oil), avocados, nuts, seeds and whole grains

  • zinc – seafood, lean meat, milk and nuts


Lobo, V., Patil, A., Phatak, A., & Chandra, N. (2010). Free radicals, antioxidants and functional foods: Impact on human health. Pharmacognosy reviews, 4(8), 118–126.

Understanding antioxidants,

Carlsen, M. H., Halvorsen, B. L., Holte, K., Bøhn, S. K., Dragland, S., Sampson, L., Willey, C., Senoo, H., Umezono, Y., Sanada, C., Barikmo, I., Berhe, N., Willett, W. C., Phillips, K. M., Jacobs, D. R., Jr, & Blomhoff, R. (2010). The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutrition journal, 9, 3.

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