Damn, Summer: Let's Learn What Electrolytes Actually Do

Dropping a plugged-in iron into the bathtub along with your body and a bunch of sudsy water will quite possibly kill you. Death is not guaranteed, but you can expect around 30 mA of current to make it from said iron through the water and into your heart, which does its pacemaking business with just barely any current at all: around 8 mA. The iron itself pulls around 15 full amps (15000 mA) from the wall and this means that, while that 30 mA is enough to stop your heart, it’s really still only less than a quarter of one percent of the total current in the appliance. (Figures courtesy of this Mythbusters webisode.) The truth is that fresh water by itself is not an especially awesome conductor of electricity.

But that’s not quite it either. To say water is a poor conductor of electricity is to ignore what makes water special—and vital. Water is what’s known as the “universal solvent”: it will fall into solution with just about any reasonable compound, like, say, salt. Most of the world’s water contains salt in solution and even more than that will contain various other minerals. Water is this good at dissolving stuff because of its peculiar chemical arrangement. H2O is what’s known as a polar molecule: the top has a positive charge, the bottom has a negative charge. The result is intense attraction to a very large variety of other molecules. The attraction between a water molecule and the chemical compound NaCl (table salt) is so strong that it can pull the latter molecule completely apart. That’s impressive.

This brings us back to electricity. Water can fairly easily change its conductivity because of its universal solvent status. It’s just a matter of having the right thing dissolved into it. With the right solute, water can become just about any sort of conductor you might want it to be or, rather, become a medium for any sort of conductor. The conductive material dissolved into water is what's known as an electrolyte. If you were to increase the salt content of our above bathtub, the conductivity of the water would skyrocket. In the Mythbusters bathtub shock experiment linked above, the waterborne current (via the clothes iron) shot up from around 30 mA to over an amp (1000 mA) without much effort.

This solvency is the basis of the phenomenon that enables all of the various cells in our bodies to communicate with each other using electrical signals, from the contractions of your heart muscle to the neurons in your brain; it also keeps your cells from overfilling with fluid and killing you. Cells have tiny water-filled pores called voltage-gated ion channels, pathways they use to communicate with their outside worlds. The water in these channels also features different varieties of salts in solution, which in effect become the “wires” of your physiology. It’s a pretty cool system.

For example, your heart does its work at the behest of electrical impulses created by movements across “action potentials” between cells, which are in turn driven by the presence of different ions, like sodium and potassium. When an ion of one of the above molecules is created, in this case by dissolving in water, it acquires an electric charge (electrons are stripped out of it by the strong polarity of water, leaving an unbalanced molecule, an ion). If enough ions collect in one place, it becomes possible to change the whole electrical polarity of that place. And if you have a enough charge built up in a certain location, relative to nearby locations, the effect is basically a hill and charge will try and “roll” down to the lower elevation (lower potential) cell. Coordinate the phenomenon, and you have current, albeit very small amounts of it. It doesn’t take much.

For table salt, the effect of dissolving in water is this:

NaCl(s) → Na+(aq) + Cl−(aq)

The Na (sodium) now has an extra electron (or electrons), which were stolen from the Cl (chlorine), which is now short of electrons. What happens next is the deliberate concentration of the sodium ions, and thus charge.

Something you don’t hear very often is that you need salt to live. Your body even needs kind of a lot of it. The reason why should be clear from the above. Without salt, all you have is plain water in and around your cells, with no dissolved medium to conduct/generate electricity. Sodium, specifically, is in part responsible for maintaining even fluid distributions around the body. If too much water (featuring sodium in solution) collects in one place, the cell will naturally expel the excess as it expels the sodium ions in an effort to maintain a proper electrical balance (more water and more sodium means more charge).

Muscle tissue, specifically, needs calcium, potassium, and sodium to function properly. Without these electrolytes, that tissue could start contracting excessively in brutal spasms or it might not do anything at all, which you would likely experience as muscle weakness or worse. Not getting enough potassium can screw up your heart rhythms and quite possibly cause a heart attack—via wacked electrical signals—and your brain’s whole ability to transmit signals is based on the ebbs and flows of sodium and potassium ions into and out of your neurons. If electrolytes fall out of balance in the brain, the result might be seizures or, again, worse.

The good news is that your body is pretty good at stuff and tends to keep its electrolytes in balance if provided with even a typically crappy American diet (though limiting sodium and increasing potassium is usually recommended, as higher sodium levels need extra potassium for everything to stay in balance). It is possible, however, to flush a whole lot of needed electrolytes from the body before they can be replenished. The common circumstance for this is at the finish lines of marathons or among other endurance sports: three or more hours of heavy exertion without replenishing some electrolytes is a ticket to hyponatremia, a condition in which your blood has a lower than needed concentration of sodium ions. The results of that imbalance range anywhere from nausea to a full-on coma and death.

Just plain water in situations like that only makes the situation worse. If you recall, sodium acts to keep water volumes within cells constant by signaling to the cell that its electrochemical situation is falling out of balance. The cell then pumps the excess water, and its sodium, back out. But without the sodium marker, the cell doesn’t realize it’s becoming overfilled and the result is cell swelling. For cells in the brain, this can be very bad, even deadly. A powerful statistic is that, of marathon running deaths, not a single one can be attributed to dehydration, while exercise-related hyponatremia deaths top 1,600. Most of those could theoretically have been prevented by drinking water with electrolytes rather than just plain water.

You don’t do that kind of exercise, probably. Your three mile jog across the Williamsburg Bridge to Manhattan and back isn’t going to throw your electrochemistry off in any too significant way. So you’re just fine with water or coconut water, which is close enough in its physiological effects to be basically the same thing. Doing crazy endurance sports, however, it’s recommended that you switch over to sports drinks, which have added sodium and potassium, or even coconut water so long as it has added sodium. The plain stuff mostly just has potassium and that’s only part of the body’s electrolyte requirements. Note that regular coconut water is absolutely not “super hydrating” or even particularly remarkable, nutritionally speaking.

My possibly gross personal contribution to this is my old post-bike ride ritual back when I lived in Maryland, an absolute pit of Hades (plus 95 percent humidity) in the summertime. This was before I knew much about this stuff and for 30 or 40 or 100 miles I’d keep myself going strictly on water and would wind up rolling back up to my house at the end of the ride actually crusted with salt around my forehead and eyebrows. My first stop inside wouldn't be the tap, but the fridge and its ubiquitous jar of pickles. Once I started, I couldn’t stop and 10 minutes later, there would just be this jar and a pile of pickles at the bottom, with every last drop of brine now on its way to my plasma and a resetting of the chemistry that allows every one of my body’s processes to function.

The point of that anecdote is just to say that when your body needs something, it's often quite adept at communicating that need.

Nowadays, for superintense workouts I wouldn’t suggest plain water, or buying coconut water or even sports drinks. It’s easy enough to make your own version that hits all of your needs just right. All it takes is regular water, some sugar to keep the taste in check (also to replace glucose/calories), baking soda (to help neutralize lactic acid buildup), plain salt, and some variety of fake salt product (which substitutes the sodium of table salt with potassium). That’s easy and you don’t have to worry about any of the other junk that might be featured in a bottle of Gatorade. Or, alternatively, you could start with coconut water and add the baking soda and salt yourself, but that also seems pretty pointless and expensive. Though I guess a bottle of coconut water is a neat way of saying hey, I do way intensive exercise without actually doing it. Your loss.

"Damn, Summer" is a semi-regular series exploring the science behind summer's various miseries and pleasures.