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Antioxidants have been credited with helping us to live longer and stay healthier. But do they really deliver on their many health claims?
The term 'antioxidant' has become somewhat synonymous with good health. In fact, the fight against ageing and chronic disease is often painted as an epic battle between good antioxidants and evil free radicals.
Food manufacturers are certainly cashing in on this notion, with everything from dark chocolate and red wine to goji berries and green tea being marketed as an antioxidant-rich superfood that will hold back the tides of ageing and chronic disease. And it's not just foods, so many of us are now popping antioxidants as supplements that they have stepped out of health food stores and onto supermarket shelves.
Yet despite their initial promise, mounting evidence from large scientific studies is showing antioxidants don't always live up to the hype when it comes to delivering health benefits. Even more concerning is the evidence which shows taking antioxidant supplements may do more harm than good.
So, what are antioxidants and the free radicals that they are supposed to fight? And what do we know about how they affect our health?
Free radicals otherwise known as oxidants are natural by-products of our cells turning food into energy.
We also encounter free radicals in many aspects of our daily lives. Sunlight triggers the formation of free radicals in our skin and eyes; they are also in the food we eat and the air we breathe. Cigarette smoke, pollution, alcohol and stress can also contribute to the development of free radicals.
Free radicals are so nasty because they are eager to react with whatever molecule they bump into. This reaction is called oxidation, and much like the oxidation that causes iron to rust or a cut apple to brown, it causes damage.
Damage caused by free radicals:
Given the constant barrage of free radicals your body encounters, it's not surprising that you come equipped with defence molecules. These molecules are called antioxidants. Some are manufactured by your body and others come from our food or supplements.
Antioxidants protect your cells by mopping up free radicals before they can bump into and damage more important molecules. Thousands of substances are known to behave as antioxidants in the presence of free radicals. And each one has its own unique biological and chemical properties, which is why there is no single antioxidant to act as a silver bullet against all the free radicals floating around your body.
Some of the most common antioxidants include:
When researchers first started linking free radicals with chronic disease and ageing, the logical conclusion seemed to be that boosting antioxidant levels, especially through supplements, would be a sure-fire antidote. But the scientific evidence hasn't panned out that way.
Early observational studies looked promising, with evidence showing people who ate diets full of antioxidant-rich fruits and vegetables were less likely to develop chronic illnesses than people whose diets were devoid of these foods. But these studies had limitations including the difficulty of knowing whether a person is healthy due to their antioxidant-laden diet, or because they likely practiced other healthy behaviours, such as regular physical activity.
To get a clearer picture, researchers started looking at supplements. In these randomised controlled trials, some participants were given antioxidant supplements and others were given no supplement, or an identical-looking dummy pill (placebo). Numerous trials on healthy people or those with underlying health issues showed there was no evidence that antioxidant supplements provide any health benefit, and for some supplements, the evidence is now clear they can be harmful.
A 2012 review, which pulled together results from 78 clinical trials and looked at over 200,000 healthy people and nearly 81,000 people with various diseases, concluded there was no evidence of benefits from antioxidant supplements. For those taking beta-carotene, and possibly vitamins E and A, there was actually an increased risk of death.
There is also some evidence that our voracious appetite for multivitamins might be thwarting other medical treatments. A study of women with breast cancer found that 70 per cent of women were taking high dose multivitamins during cancer treatment. The authors called for more research to establish whether supplements could be undermining their treatment regimes by mopping up the cancer fighting free radicals generated by radiation therapy and some forms of chemotherapy to attack cancerous tissue.
Other research suggests antioxidants could reduce the health-promoting effects of exercise. During exercise, muscles go into metabolic overdrive, consuming far more energy and producing far more free radicals than at rest. But these free radicals may actually be integral to some of the health benefits exercise brings. (Although free radicals are associated with harmful events in the body, they are also vital to some important body processes.) There is evidence that gym junkies and athletes who try to combat the extra free radicals with antioxidants may be preventing their body from getting the full benefits from exercise.
That a diet full of fruit and vegetables is healthy still stands, but how much this is due to the antioxidants you eat or drink remains unclear.
And despite the ravaging effects that free radicals can have on healthy tissues, quelling their production with supplements is not necessarily a good thing in fact when it comes to some supplements you might actually be doing more harm than good.