Topic Review: Antioxidants

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ORIGIN STORY

Cyanobacteria and the evolution of antioxidants

For the first 2 billion years of its life, earth’s atmosphere had no oxygen. As humans, we would die very quickly in those prehistoric conditions. Today oxygen makes up ~21% of the air we breathe and is vital to sustain life.

Oxygen started to appear about 2.4 billion years ago from a tiny photosynthetic Cyanobacteria. Up until that moment, life on earth was unicellular and anaerobic, meaning oxygen was toxic to life. Known as ‘The Great Oxidation Event‘, those prehistoric organisms had a stark choice the moment oxygen began increasing in the atmosphere: evolve to produce ‘antioxidants’ to protect themselves against oxidation, move to anaerobic environments or die.

Some organisms buried themselves deep in the mud to flee the oxygen (where they exist today), but many became extinct. Some cyanobacteria however evolved to produce anti-oxidants that allowed them to survive in an oxygenated environment. “Over time more advanced antioxidant systems evolved, allowing Cyanobacteria to adapt to an aerobic lifestyle and become the most important environmental engineers in Earth history” says geobiologist Professor Woodward Fischer from Caltech says in a 2016 article.

Plants evolved from cyanobacteria and therefore, also evolved to produce an array of antioxidant compounds including carotenoids, flavonoids, benzoic acids, folic acid, ascorbic acid. As more advanced life evolved within an oxygenated atmosphere, humans also evolved an effective antioxidant system to combat the damaging oxidation. Increased melanin in skin (tanning) in response to exposure to UV radiation is an example of an antioxidant response in the skin. The real debate today however, is whether consuming additional dietary antioxidants can help humans protect themselves against disease and live longer. The evidence is not clear.

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THE CONSENSUS

Are more antioxidants better for you?

100% Negative via 3 experts

Antioxidants can short-circuit the damage caused by free radicals so it seems logical that taking more antioxidants from supplements would be healthier? Clinical trials have failed to substantiate this says Dr Homer Black, biochemist from Taylor College of Medicine. And some antioxidants have been shown to be harmful.

“A number of epidemiological studies (principally case-control) have found inverse associations with carotenoid levels (both dietary intake and blood levels) and cancer risk. However, clinical trials have failed to substantiate such a relationship and one even found an 18% increase in lung cancer among male smokers receiving beta-carotenoid supplements.

Recent experimental evidence seems to indicate that beta-carotene, per se, acts as a pro-carcinogenic agent in UV-carcinogenesis when provided as the only carotenoid and phytochemical in the diet. What the public must understand is not all antioxidant mediated reactions are beneficial and antioxidants such as beta-carotene can, under certain conditions, act as a pro-oxidant” says Dr Homer.

Nutrition scientist Dr Tim Crowe confirms this: “Vitamin A as beta-carotene has been associated with a reduced risk of certain cancers, but an increase in others, such as lung cancer in smokers, if vitamin A is purified from foodstuffs.”

Experts caution about taking antioxidant supplements. “The notion that antioxidants per se have superpowers in terms of preventing or curing disease has been put to rest long ago” says Professor Jens Lykkesfeldt, a biochemist from the University of Copenhagen. “ingesting enormous amounts of antioxidants does not necessarily improve your health…Clearly essential micronutrients such as vitamin C that are also antioxidants are good (essential) for you. However, the notion that antioxidants per se has super powers in terms of preventing or curing disease has been put to rest long ago. It is therefore important to distinguish between essential micronutrient that happens to be antioxidants (and are important for humans health) and other ‘generic’ antioxidants that very common in e.g. fruits and vegetables that are not individually essential.”

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THE CONSENSUS

Do antioxidants help protect against cancer?

Uncertain via 4 experts

Read the full answers to this question here. “The idea that antioxidants, consumed in green leafy and yellow vegetables, are cancer protectants arose from a 1981 epidemiologic study in which individuals consuming a greater amount of these vegetables were at a lower risk for cancer” says Dr Homer Black, biochemist from Taylor College of Medicine. “As these vegetables were rich in carotenoids such as beta-carotene, and knowing that beta-carotene was a strong singlet oxygen quencher and antioxidant, it was proposed that this carotenoid, or related carotenoids, might act as a cancer preventive. Whether these carotenoids can reduce cancer risk is unclear and controversial.”

“Cancer patients often take antioxidant nutritional supplements during cancer treatment to alleviate treatment toxicities, improve long-term outcomes and replenish antioxidant status that declines during cancer treatment ” says Nutrition scientist Dr Cornelie Nienaber-Rousseau “However, summaries of the scientific studies on antioxidant supplements (beta carotene, vitamin A, vitamin C (ascorbic acid), vitamin E, and selenium) for prevention of cancers found no evidence that they prevent cancers (Bjelakovic et al., 2004). In fact antioxidant supplements (beta carotene, vitamin A, and vitamin E) seem to increase overall mortality (Bjelakovic et al., 2004; Bejelakovic et al., 2007)” she writes.

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THE CONSENSUS

Are antioxidants overhyped?

Likely via 5 experts

Read the full answers to this question here. Experts suggest most of the hype on superfood antioxidants don’t match the science, particularly with regard to taking supplements as “intake needs to be controlled according to usage as some of these can be overdosed (Vitamin A, Vitamin E and selenium are toxic in high doses)” says Professor Vissers from University of Otago.

The good news is that evidence seems to suggest that whole foods are more effective than supplements says Dr Tim Crowe: “There is increasing evidence that antioxidants are more effective when obtained from whole foods, rather than isolated from food and presented in tablet form with some antioxidant supplements actually increase cancer risk”. “Antioxidants should preferably come from food and not be supplemented”, says Nutrition Scientist Dr Cornelie Nienaber-Rousseau.

What about superfoods?

“Despite the marketing hype, antioxidants found in so-called superfoods [like goji berries, blueberries or pomegranate juice] are no more effective than those in regular fruit and veg, so you’re better off saving your money” writes Dr Jacqui Adcock from Deakin University in The Conversation.

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There is reasonable evidence that following a diet that contains more fruits and vegetables can be protective of some cancers. This is reviewed in a report by the World Cancer Research Fund (Third Expert Report on Diet, Nutrition, Physical Activity and Cancer: A Global Perspective).

The protective effects of fruits and vegetables are likely due to the combination of compounds present in those foods, not just compounds that have antioxidant activity. This combination would be very hard to replicate in a pill. In considering foods associated with cancer prevention, diet as a whole needs to be taken into account (in other words, the things one eats with the vegetables) as well as whether or not the calories eaten are expended (aka energy balance). It is difficult for the beneficial effects of a good diet to be exerted in the face of a positive energy balance that leads to weight gain.

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TAKEAWAYS

1. Antioxidants do serve important roles in our body and diet is an important source of them to maintain health.
2. Antioxidants are not just one molecule, our supply can come via many different vitamins and minerals. Plant-based foods are rich in antioxidants and also contain thousands of other plant chemicals that likely benefit our health more than antioxidants alone.
3. Evidence suggests antioxidant supplements do not work as well as the naturally occurring antioxidants in whole foods such as fruits and vegetables.
4. Antioxidants found in so-called superfoods [like goji berries, blueberries or pomegranate juice] are no more effective than those in regular fruit and vegetables.
5. Be very wary of antioxidant supplementation (see 3.) as evidence shows it can be harmful.
6. Experts say there’s too much hype on antioxidants. Save your money on supplements or superfoods – just maintain a diverse diet with lots of fruits and vegetables.