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We all know that we need things like water and oxygen to live, but what happens when you get too much? Join Hank Green for a new episode of SciShow and learn how too much of a good thing might actually kill you.
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Look at your body. It’s pretty great, right? Doing all this complicated stuff to keep you alive? Well, your body runs by the grace of a delicate balance, maintaining just the right levels of the materials you need to live: water, salts, oxygen, even your own blood cells. And you already know that getting too little of something, like water, or air, or a vitamin or nutrient, is, medically speaking, bad. Like, leads to death. But things that are considered healthy, or beneficial, or even essential can be just as dangerous, in the wrong amounts. In fact, many vital substances, including some that you’re taking in right now can totally do you in, if you end up ingesting just a little too much of them. So consider yourself warned.


You know how important water is to your body. I mean, seeing how it accounts for more than 60 percent of your total body mass, you pretty much are water. And the water in your body performs a lot of important functions. But one of the most important happens when it combines with ions from dissolved minerals like sodium and potassium, which you probably know as electrolytes.

Your cells use different concentrations of these electrolytes to create the positive and negative charges that regulate your internal electrical system. This is what you use to power your moving and thinking and everything else that your body does. Which is why dehydration is no joke. Without enough water, the loss of electrolytes can lead to the biological version of an electrical blackout, taking power away from your vital organs, including your brain and your heart.

But what you might not realize, is that drinking too much water can be equally dangerous. Yeah, it turns out those urban legends about folks dying from drinking too much water aren’t legends at all, and death by water intoxication is a thing. Fraternity hazing ceremonies and radio-station contests that dared people to chug a bunch of water have actually ended in deaths. And so have over-zealous attempts to rehydrate after running marathons, or hiking in hot weather, or after long, drug-fueled dance parties.

The condition is called hyponatremia, or “insufficient salt in the blood,” and it basically means you’ve diluted your blood too much for your electrolytes to do you any good. Chug six liters of water in a sitting, and your kidneys probably won’t be able to flush it through fast enough to re-establish a proper balance. Instead, all that extra water starts seeking out higher concentrations of electrolytes, especially ions like sodium, in your cells. Which makes your cells swell up like water balloons.

The lack of electrical power is a big enough problem on its own. But some of your cells just can’t take on that much water. The neurons in your brain, for example, are jam-packed tight into your skull, and don’t have much room to expand. That’s why the brain swelling, or cerebral edema, caused by too much water is so dangerous. It can lead to seizures, coma, brain damage, and death.

In the end, death by dehydration and death by water intoxication have a lot of the same symptoms, and the same mechanisms, in common because they’re really the same problem: an imbalance of water and electrolytes in the body. Another kind of substance that can easily become too-much-of-a-good-thing? Antioxidants. You see them touted on food labels all over the place these days, but what are antioxidants, and why should we be eating them?

Well, in a nutshell, antioxidants are molecules that can help prevent, or at least delay, certain types of cell damage, caused by oxidation. To understand how this works, we’ve gotta first talk about the threats that they help neutralize: free radicals. Now that might sound like a 90s garage band, but free radicals are potentially dangerous atoms or molecules with an extra, unpaired electron. This unpaired electron make a free radical lonely and unstable, so desperate to find another electron that it’ll snatch one from anything it can. And when it does snag one from another molecule, say, one from your cells, it oxidizes it, or causes it to lose an electron. This electron-theft can cause oxidative stress, damaging your cells and their structures, including your DNA.

Thankfully, our bodies produce antioxidants that can help neutralize many free radicals. And we also get extra help from antioxidants in certain foods. Fruits and vegetables naturally provide lots of antioxidants, like beta-carotene, lutein, and vitamins A, C, and E. These compounds can give a free radical one of their own electrons, to basically shut it up and end its destructive rampage. So they are considered beneficial, and few, if any, concerns have been raised about getting too many antioxidants in your diet.

But you can’t say the same for taking antioxidant supplements. When you eat a handful of blueberries or a piece of dark chocolate, you’re ingesting a bunch of different types of antioxidants. And it turns out that they need to work together. See, when an antioxidant gives an electron to a free radical, it briefly becomes unstable. But when other antioxidants are around, it can take an electron from one of them. And that electron donor, in turn, will bum one from someone else. This free swapping of electrons works best among different kinds of antioxidants. But, if you take a mega-dose of a single kind, like vitamin C, you don’t have other kinds around to help re-stabilize those vitamin C molecules after they’ve done their job. This means you can actually end up with a lot more unstable molecules floating around your body, which is the opposite of what you wanted in the first place. So, I’m not saying that supplements are going to kill you or anything, although extreme oxidative stress definitely can do permanent harm, which I will explain in a bit.

But for now, the thing to know is that the balance between free radicals and antioxidants is more complicated than we used to think, and taking high doses of antioxidant supplements can just muck it up.

But what about maintaining the right balance of things you don’t ingest, or probably even think about? Like your own blood? Blood distributes nutrients, gets rid of waste, clots wounds, and prevents infection. It does this all using four, well-balanced components. You’ve got red blood cells carrying oxygen around, white blood cells to help fight infections, and platelets to help with clotting. And all of these float around in plasma made up of water, sugar, sodium, protein, and fat. The average adult body contains about 5 liters of blood, and we all know that you can quickly die if you lose too much of it. Maintaining the right volume of blood is important, and we’ve talked before about how a lot of so-called “doping” in professional sports actually involves tinkering with your blood volume.

But having the right amount of blood cells is also key to maintaining your body’s balance. And most of the imbalances that occur here are usually caused by medical conditions. You’ve probably heard how a low blood-cell count can be a sign of trouble, like cancer or HIV/AIDS. But more is definitely not better when it comes to blood cells.

An overproduction of white blood cells, for example, is known as leukocytosis. And even though white blood cells are the white knights of your immune system, this condition actually suppresses your immune response. Leukemia is perhaps the most well-known disorder associated with excess white blood cells. It’s a blood cancer that occurs when a person’s bone marrow starts churning out immature and abnormal white blood cells. Unlike their healthy kin, these cells can’t actually fight infection. And they don’t die when they should. Instead, they keep dividing and multiplying, until they crowd out healthy red blood cells and platelets. Eventually, the body winds up being unable to adequately fight infection, carry oxygen, or stop bleeding. Likewise, a mutation in bone-marrow cells can cause the overproduction of red blood cells, like in the case of a different type of blood cancer, called polycythemia vera. In a healthy body, red blood cells account for about 45 percent of the blood. But in people with conditions like polycythemia, the blood can get too thick, increasing the risk of blood clots, heart attack, and stroke.

But now, to oxygen. Surely that’s something you just can’t get too much of, right? Yeah, no. And frankly, by now you really shouldn’t be surprised to hear it, because: balance! I think we can all agree that oxygen is generally a good thing. In fact, it’s probably the most important thing. You can go weeks without food, days without water if you have to, but without oxygen you could die within minutes.

The air we breathe is about 21 percent oxygen. And when you inhale, your red blood cells grab the O2 from your lungs, and pass it off to other cells, which use it for cellular respiration, the process of breaking down sugar to create chemical energy. So without oxygen, your cells wouldn’t have the energy to do anything. And yet, while they would quickly die without enough oxygen, they would die even faster with too much.

So-called oxygen toxicity can happen when the body is flooded with oxygen too quickly, usually in a hospital setting, like when a person’s being resuscitated from a heart attack or stroke, or when a premature baby is getting some help breathing. Basically, the risk here is from our old foe oxidative stress. You know about the threat posed by free radicals, which run around oxidizing just about anything they can snag an electron from. But nothing oxidizes like oxygen!

Oxygen itself is super needy, with two vacancies in its outer electron shell that it would just love to fill up. On its own, oxygen can go around your body creating free radicals, which go on to steal electrons from other molecules. Of course, our bodies produce antioxidants to repair the damage that all of this oxygen can cause. But we’re used to dealing with the stress caused by living in a 21 percent oxygen environment, not 100 percent!

And in the past decade or so, scientists have discovered that giving patients 100 percent oxygen creates hordes of free radicals that can cause all kinds of tissue damage. In 2008, for example, researchers in Texas found that oxygen-deprived baby mice that were treated with 100 percent oxygen experienced brain damage, and exhibited symptoms similar to cerebral palsy. Why? Well, all that oxygen created a wave of free radicals that caused enormous oxidative stress, doing special damage to the cells that make myelin, the fatty insulation that covers nerve cells. But the researchers were able to treat some of the harmful effects by giving the mice antioxidants. Of course, only in the proper amounts.

So, the take-home message here is that your body maintains specific balances for good reason. You live in a complex world with special, precious amounts of what you need to survive. And you are set up to take in only what you need, and use only what you take. So when it comes water, or oxygen, antioxidants, or your own blood cells, you can end up having too much of a good thing.

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