Antioxidants are the master of the health halo: put them in a yogurt, and that yogurt is now a health food. Marketers took that idea and ran, but the science was slim -- and the more they research the more scientists find out that antioxidants aren't the magical disease-shield we've been led to believe.
Illustration by Tara Jacoby.
It's a shame because the theory behind antioxidants is simple and beautiful: Free radicals contribute to ageing, cancer and other things we don't want, and antioxidants neutralise those free radicals. Therefore, antioxidants must slow ageing, prevent cancer and generally promote health, right? Get extra in your diet -- or take a shortcut by popping pills -- and you'll be a better person for it. But that's not the whole story.
How Our Bodies Use Antioxidants
To understand antioxidants, we have to zoom way in to the atoms that make up our cells. All of the molecules in our bodies -- things like DNA and proteins -- are made of atoms held together with pairs of electrons. In general, electrons are happiest and most stable when they are in pairs.
So it's too bad that free radicals -- molecules with odd numbers of electrons -- sometimes end up in our cells. They may steal an electron (to complete the pair) from whatever they bump into, turning their victim into a free radical that can go on to damage something else.
This is a problem: Too much damage from free radicals can kill a cell. Cell membrane damage can lead to cells not functioning properly. DNA damage can lead to cancer.
This is where antioxidants come in: like bodyguards willing to take a bullet, antioxidants can react with free radicals, neutralising them and thus protecting the other molecules in the cell.
Where Antioxidants Come From
Our cells have complex, well-regulated systems to manage the stress of being occasionally overrun with free radicals. Some of the components of these systems are homegrown, and others we get in our diet as vitamins and minerals. For example, Vitamin E, Vitamin C, and glutathione reductase work together as an antioxidant team. Glutathione contains selenium, a mineral we get from our diet. That's why these vitamins and minerals are considered essential for us to eat.
Plants have antioxidant systems too, which are the source of a lot of the antioxidants in supplements and superfoods: green tea, red wine, cocoa, and berries to name a few. Fruits and vegetables, in general, contain a ton of antioxidants.
Chemicals can have antioxidant properties aside from whatever other function they perform, so there isn't just one type of antioxidant; there are thousands. It's probably not fair to lump them all together. Some may be useless without other members of their team; some may work better for certain purposes or in certain contexts than others.
Antioxidants Work In the Lab...
So far, antioxidants are sounding pretty awesome. We have a solid scientific theory: free radicals are bad, antioxidants neutralise free radicals, therefore antioxidants are good.
We can do some simple experiments to show that antioxidants "work," at least in the lab. You can do them at home, too.
Oxygen is a common source of free radicals; it easily breaks apart, sometimes with the help of sunlight, into free radicals called reactive oxygen species. The act of stealing electrons is called oxidation (whether free radicals are involved or not). When metal rusts, that's a form of oxidation. When apples or avocados turn brown from exposure to air, that's also oxidation.
So you can cut up an apple in your kitchen, but prevent it from turning brown by dunking it in a solution of vitamin C, one of our classic antioxidants. It's such a slam-dunk idea you can buy vitamin C by the jar if you do a lot of apple slicing.
This explains why antioxidants like vitamin C are in so many processed foods and cosmetics: they're preservatives. They prevent damage to the cells of the applesauce, or the pigments that give the juice its colour, or the fatty acids that make up part of the lotion. Plus the makers get to put "contains Vitamin C!" on the label, which makes you think it's healthier.
...But They Often Don't Work in People
Maintaining human health for years, though, is more complicated than conducting kitchen experiments. In the 1990s, antioxidants held a lot of promise, and health-conscious people started taking them to try to be healthier. For a while, this bolstered antioxidants' good image: if you look at people who take antioxidants (or who eat a lot of fruits and vegetables), you'll find that they tend to be pretty healthy.
But this is the classic flaw of observational studies: you can't prove that one factor (antioxidants) causes the other (good health). For that, you need to give some people the antioxidant while withholding it from others, and see whether the supplement made a difference in their health. Here's how the National Cancer Institute sums up those years of research:
Overall … nine randomised controlled clinical trials did not provide evidence that dietary antioxidant supplements are beneficial in primary cancer prevention. In addition, a systematic review of the available evidence regarding the use of vitamin and mineral supplements for the prevention of chronic diseases, including cancer, conducted for the United States Preventive Services Task Force (USPSTF) likewise found no clear evidence of benefit in preventing cancer.
So, while antioxidants do help fight free radicals in your body, they aren't a miracle cancer prevention. (That study also looked at prevention of heart disease, and likewise found no benefit.)
In one famous trial, smokers took beta-carotene to lower their risk of cancer. Instead, those who took the supplement got more lung cancer. And heart disease. And were more likely to die of all causes.
Meanwhile, research on reactive oxygen species -- those nasty free radicals -- has turned up evidence that they're not even all bad. They seem to help in wound healing, for example. And even though antioxidants are supposedly an anti-ageing ingredient in skin products, reactive oxygen species may be beneficial for skin, at least in young people -- which means those antioxidant creams could be doing the opposite of what the label claims. (The Telegraph has a report on that research here.)
Exercise increases the amount of free radicals in your cells, which led athletes and trainers to praise antioxidants as a tool to help post-exercise recovery. But trials of antioxidants for athletes found the opposite: large doses may impair your ability to build muscle, as reported in the journal Physiology. The New York Times breaks it down here.
We Don't Know Much About What Antioxidants Really Do
Don't take these less-than-promising results the wrong way: you don't need to avoid antioxidants in your diet. Blueberries and green tea are still good for you, even if they're not cancer-preventing "superfoods."
There's a lot of confusion in health and nutrition, but everyone agrees on this: fruits and vegetables are good for you, they contain the vitamins that we know we need, and most of us don't get enough. Before you worry about extra antioxidants, fix that likely flaw in your diet. As Time magazine reported:
For most healthy adults, the antioxidants contained in a healthy diet rich in fruits and vegetables would be enough to combat most of the free radical damage occurring in their bodies. But, says Jeffrey Blumberg, director of the antioxidants research laboratory and professor of nutrition at Tufts University, most people fall far short of meeting recommended daily intakes for vitamins like C and E.
If you are falling short, a multivitamin could help -- or you could just do what everyone has been telling you since childhood and eat your veggies. If you like chocolate, eat it because it's delicious, not because it's healthy. Don't guzzle gallons of acai juice, and don't waste your money on antioxidant supplements; they probably do more for the sellers' bank account than they do for your health.
Disappointed by the uncertainty? Flip-flopping of scientific opinion is a good thing, even though it's frustrating for us sometimes. It means that scientists didn't just dunk an apple in vitamin C and crown antioxidants the Miracle Cure For Everything in perpetuity. Biochemistry is complicated, and with each lab experiment and observational study and clinical trial we are getting closer to understanding how these fairly simple chemicals affect something as big and complicated as our health.
What could explain the contradictions we're seeing? It's possible that a little reactive oxygen is ok but a lot is bad (or vice versa), or that some of the thousands of antioxidants are good for us but others are not. Perhaps antioxidants are helpful against some diseases but worsen others, and we'll have to make some tough decisions.
In other words, maybe we'll have to balance risks and benefits, just like we do with drugs or other medical decisions. And we'll be glad that the flip-flopping scientists persevered enough that we can understand what those risks and benefits are.
Lifehacker's Vitals column offers health and fitness advice based on solid research and real-world experience.