Previous: These Smart Roads Could Change the Future of Driving
Next: 6ish of Your Everyday Actions, Explained | Compilations



View count:193,774
Last sync:2022-11-20 14:15
There's evidence that antioxidant-rich diets have health benefits in humans, but the antioxidant chemicals and enzymes seem to be only part of the puzzle.

Hosted by: Hank Green

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at
Support SciShow by becoming a patron on Patreon:
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Avi Yashchin, Adam Brainard, Greg, Alex Hackman, Sam Lutfi, D.A. Noe, Piya Shedden, KatieMarie Magnone, Scott Satovsky Jr, Charles Southerland, Patrick D. Ashmore, charles george, Kevin Bealer, Chris Peters
Looking for SciShow elsewhere on the internet?

It seems like every week there's a news article claiming you should consume more antioxidants, be it through fancy smoothies or science-y sounding supplements.  This antioxidant craze goes back a long time to the 80s and early 90s when some early research suggested antioxidants could maybe protect against certain diseases.  Food and supplement companies jumped on that research and have been touting the benefits of antioxidants ever since, but the follow-up research investigating those benefits has actually been pretty inconsistent and scientists aren't totally sure why yet.

Health food commercials will give you the impression that an antioxidant is a thing, a healthy thing that you should be eating and drinking, but chemically, the word 'antioxidant' is actually more of an adjective than a noun.  It describes a range of chemicals and enzymes that can neutralize free radicals, compounds with single, unpaired electrons. 

Free radicals can cause real havoc in our cells, altering DNA, damaging the proteins our cells need to function, and messing with the sophisticated membranes holding everything together, and these free radicals can come from practically anywhere, from the food we eat to the air we breathe, even sunlight can produce free radicals in our bodies.  Now our cells try to contain them by employing a large network of antioxidant chemicals and enzymes to deactivate the different types of free radicals our bodies encounter, but the amount of free radicals being produced outpaces the rate at which our bodies can quench them, our cells enter a state known as oxidative stress. 

Unfortunately, slipping into a bubble bath and decompressing with an episode of Queer Eye is not a viable way for our cells to destress, though that does work for my mind, and if our cells stay oxidatively stressed for long periods of time, there can be serious health consequences.  In the 80s and 90s, scientists started gathering evidence that cancer, heart & neurodegenerative diseases, the negative side effects from aging could all be linked to damage from oxidative stress, at least in part.  Research during that time also found that a Mediterranean diet, which is rich in antioxidants, was associated with a lower incidence of those diseases.  Scientists put two and two together to develop the hypothesis that supplementing peoples' diets with antioxidants might prevent or even reverse the problems associated with these diseases.  

It's an elegant idea, but unfortunately, it's been difficult to find support for.  Researchers began by looking at how supplementing single antioxidant chemicals would affect cells grown in test tubes and saw some promising results.  For example, studies showed that chemicals like vitamin-E could successfully act as antioxidants to reduce damage from oxidative stress in cell membranes, but when they tried to extend the benefits that they saw in cell cultures to randomized clinical trials with real humans, taking those same antioxidants, they found inconsistent effects.  

For instance, in a study called the Women's Health Study published in 2005, a group of almost 40,000 women took either a vitamin-E supplement or a placebo every other day for 10 years.  That is a big study population, which should enable you to see robust results.  The rates of cancer and heart disease were unchanged compared to control, but researchers did observe a 24% reduction in heart-related deaths in the group who took the vitamin, except another study published in 2005 which tracked nearly 4,000 people over seven years found that vitamin-E supplements increased the risk of heart failure, which would indicate an increased risk of heart-related mortality, the opposite of what the first study showed, and such contradictory claims about antioxidant supplements are so common in the field that it's virtually impossible to take the findings of any individual study at face value.

In fact, a meta-analyis of 78 randomly controlled trials with a combined sample size of almost 300,000 people of various health backgrounds found antioxidant supplements to have no net beneficial effect.  The one exception for supplements is that a combination of three antioxidants moderately reduce the risk of age-related eye disease, which, yay.  It's something, we guess.  Despite the lack of reliable evidence for antioxidant supplements, though, many studies have found that people who follow diets containing fruits and vegetables rich in antioxidants have lower incidence of diseases related to oxidative stress, so we can see benefits from antioxidant supplements in a petri dish.  We can see benefits from antioxidant-rich diets in people, but we can't seem to demonstrate any benefit from antioxidant supplements in people.

It could be a simple problem of dosage.  We may be over or under administering these antioxidants so they're not doing the job we want.  It could also be that our cells compensate for the elevated antioxidant levels from supplements by slowing down their own antioxidant production, so overall in our bodies, the levels don't change, or maybe it's just that individual antioxidants are not effective at protecting against a disease in large organisms.  Instead, we may need a wide variety of antioxidants rather than just one at a time.  You know how we said that our bodies use a variety of antioxidants?  Naturally, that's true of fruits and veggies, too, and that variety might help our bodies deal with the wide variety of free radicals we naturally encounter.  Each antioxidant compound acts a little differently, so if someone has an excess of a particular free radical, giving a high dose of the wrong antioxidant could be like giving a band-aid to someone with the flu, just not the right treatment.

It might also be that studying nutrition is just plain hard and we have a whole video on why that is, which we'll put a link to at the end of the video.  Whatever the reason, antioxidant supplements don't have much evidence to recommend them.  That's even though we know the chemistry and even though we know having them in your diet is linked to beneficial effects.  Our bodies are complicated and science is weird about connecting dots sometimes, but that's why we do it, to really know what we know, and right now, we just don't know about those antioxidant pills.

Thanks for watching this episode of SciShow.  Our amazing Patrons help us do what we do every day, and that includes making this video.  Thank you to all of our Patrons.  If you'd like to join them, you can do that at