There is a reason that governments and health authorities around the world spend millions promoting the idea of eating a certain number of servings of fruit and vegetables each day, it is because they are loaded with antioxidants. Those who have a diet rich in antioxidants from fruit and vegetables have been shown to have a reduced incidence of certain diseases. However, research suggests that high doses of antioxidants in supplement form, such as in your standard multi-vitamin, can actually have a negative impact on health.

What are antioxidants?

An antioxidant is a molecule that prevents oxidation, a chemical reaction that results in the production of free radicals, which begin a chain reaction that can damage or destroy cells. While oxidation reactions are an essential part of any organism’s life cycle, too much too often can be highly damaging, increasing the risk of certain forms of cancer and cardiovascular disease.

Diets rich in fruit and veg have been shown to correlate with reduced risks of these diseases, with early epidemiological studies identifying beta-carotene (which converts into vitamin A), ascorbic acid (vitamin C) and the tocopherols (vitamin E) as some of the most potent and protective antioxidants1.

This is why antioxidants have been marketed as the elixir of life, because they help neutralise the damage caused by free radicals.

The logic follows that if antioxidants mitigate the damaging effect of free radicals, then supplementing them can potentially prevent a host of serious health implications, right? Not so fast.

Why supps can cause problems

Free radicals perform essential functions within your cells as important signalling molecules. Introducing pharmacological doses of exogenous antioxidants can consequently interfere with defence mechanisms, such as phagocytosis (an immune system response where a cell consumes a particle, such as bacteria), apoptosis (programmed cell death), and detoxification (the removal of a toxic substance)2.

As a result, more stable radicals are formed, which can move deeper into lipoproteins or cells and potentially cause damage to the lipids or DNA3. They may also increase cell proliferation, along with mutations because of DNA damage, which can result in the formation of cancerous cells3.

Intervention studies originally set out to confirm the findings of the epidemiologic studies, but actually found potential adverse effects from antioxidants given in supplemental form, through a pro-oxidant effect which leads to an increase in cancers, heart disease and morbidity4.

One study reported that subjects who received beta-carotene supplementation actually developed a higher incidence of lung cancer, and vitamin E supplementation at a dosage >150 IU per day resulted in an increase of all-cause mortality, with the risk of mortality progressively increasing up to doses ≥ 400 IU per day5.

Real food is best

Therefore, taking a multi-vitamin containing antioxidants will be no substitute for a diet lacking in essential nutrients. On going consumption of pharmacological doses of antioxidants has been shown to directly increase probability of early morbidity, so the average ‘health conscious’ multi-vitamin consumer could be doing more long-term harm than good.

Although low-dose supplementation of some vitamins may be beneficial in certain cases if you are deficient or unable to follow a healthy diet, the truth is real foods have hundreds (if not thousands) of different nutrients that work synergistically. Taking just one or two isolated nutrients won’t have the same beneficial effects. Eating a balanced diet which includes a variety of vegetables and fruit every day will be a far better health insurance policy than your standard multi.


  1. Frei B (1994) Reactive oxygen species and antioxidant vitamins: mechanisms of action. The American Journal of Medicine. 97(3A), 5S-13S.
  2. Bjelakovic G, Nikolova D, Gluud L, Simonetti R, Gluud C, (2007) Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary Prevention Systematic Review and Meta-analysis, The Journal of the American Medical Association, 297(8), 842-857.
  3. Gonzalez M, Riordan H, Miranda-Massari J (2002) Vitamin C and Oxidative DNA Damage Revisited. Journal of Orthomolecular Medicine, 17(4), 225-228.
  4. Rietjens I, Boersma M, de Haan L, Spenkelink B, Awad H, Cnubben N, van Zanden J, van der Woude H, Alink G & Koeman J (2002) The pro-oxidant chemistry of the natural antioxidants vitamin C, vitamin E, carotenoids and flavonoids, Environmental Toxicology and Pharmacology,11, 321–333.
  5. Miller E, Barriuso P, Dalal R, Riemersma D & Rudolph A; (2007) Meta-Analysis: High-Dosage Vitamin E Supplementation May Increase All-Cause Mortality, Annals of Internal Medicine, 142(1), 37.
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