Revisiting the Myth: Does Coffee Dehydrate Us?
A commenter fears that the caffeine disrupts our electrolyte levels
In a recent article debunking health misinformation claims, I pointed out that coffee is not dehydrating us. Specifically, the claim was that coffee is a terrible morning choice, because “we are already dehydrated.” The implication here is that coffee uses up water from our body.
It doesn’t. This is a myth.
I’ve researched this before. There are sources. Caffeine is a diuretic, meaning it makes us pee, but coffee is also full of water.
This didn’t go down well with everyone. One commenter challenged this. Here’s their comment:
You are fan of science then about this you should already know that coffee amd especially caffeine — as it is duretic — and you wrote it, is removing important electrolities.
You also should know, ased on science, that dehydration isn’t only about water (you do like scientific information, correct?) but also — about minerals. And you can intake a lot of water AND STILL be dehydrated.
‘Caffeine, a diuretic, increases urine output, which can lead to the excretion of more minerals, including magnesium.’
And then it doesn’t matter, that you gave water in the coffee — as the same moment this water is useless, due to diuretic effect that clean body from important minerals.
Let’s dive into this. Electrolytes (and even “electrolities”?) are important to our health. We don’t want to disrupt them, and we also don’t want to lose our precious minerals.
Electrolytes, they’re what plants crave
People are, essentially, big squishy bags full of water. But it’s not pure water; it’s water with minerals dissolved in it!
Minerals, when dissolved in water, are called electrolytes. They’re called this because they allow water to carry an electrical charge.
(Fun fact: water, on its own, is an excellent insulator. But salty water can conduct electricity. If you are going to be electrocuted, it’s better if you’re in saltier water, so the water can conduct some of the electricity away from your body.)
There are lots of different dissolved elements in the body, acting as electrolytes: sodium, chloride, potassium, calcium, magnesium, and phosphate, to name a few.
We gain electrolytes through our diet. When you eat salty food, your body absorbs some of the salt to mix with your bloodstream.
We lose electrolytes through a few different ways:
Sweating
Urinating
Diarrhea and vomiting
And that’s okay. The body maintains a balance of electrolytes. Losing them is not bad; we constantly absorb and excrete them.
Caffeine’s effect on electrolytes
So what about our morning coffee? What’s that do to our electrolyte levels?
Caffeine is, as I mentioned above, a mild diuretic. This means it stimulates the body to produce more urine. (Another fun fact: caffeine tolerance also provides tolerance against its diuretic effect! If your cup of coffee isn’t doing much to wake you up, at least it’s not going to increase the frequency of your bathroom trips.)
When we pee more, we lose more electrolytes. In order to get water into the bladder, our kidneys push salt across their membranes. It doesn’t take a lot, but there’s a mild amount of electrolyte loss with each trip to the bathroom.
But caffeine doesn’t do much to move the needle. A 2002 review found that caffeine consumption had no statistical impact on the electrolyte balances of athletes. A 2009 paper found caffeine increased the amount of electrolytes lost to sweat, but not to the point of disrupting electrolyte levels in the body.
There is one case report of a man who was hospitalized from electrolyte loss due to caffeine; he’d consumed more than 15 cups of coffee per day, every single day.
Moderate caffeine intake will not throw off your electrolyte levels.
Drinking water but still dehydrated??
Perhaps my second-favorite part of this comment on my piece was this: “And you can intake a lot of water AND STILL be dehydrated.”
I am pretty sure this came from a Google AI-generated answer, but there’s some truth to it. If you do have an imbalance of electrolytes, drinking more water alone doesn’t help, because there’s not enough salt in the body to properly absorb it.
(Water flows from less-salty areas to more-salty areas, to balance it all out in equilibrium. The higher salt levels in the body — due to electrolytes — help water absorb into the body.)
But, again, most of us do not have an electrolyte imbalance.
There’s tons of salt in our diet. Sodium and chloride, the most common electrolytes? You’re eating too much, not too little.
And if you are worried about other types, like magnesium or calcium, the answer is some nuts or leafy greens. It’s not a supplement; it’s a salad.
A lot of the search results about electrolytes are published by companies that, surprise surprise, sell supplements. If you aren’t sweating out literal puddles, working out for multiple hours or in a high-heat area that increases sweating, you don’t need a Gatorade.
And one last nail in this coffin? Coffee contains electrolytes. It’s actually a decent source of potassium, with about 120 mg in 8 ounces of dark roast.
My favorite thing about this comment left on my story? It ended with this:
So if you really want to base on science — take into consideration ALL FACTS, not only those that are supporting your wishfull-thinking, as right now — you looked quite anti-scientific.. 🤷♀️
The Mayo Clinic says most caffeinated drinks are balanced by the fluid in the drink; they’re not dehydrating.
A peer-reviewed publication demonstrated that caffeine doesn’t significantly affect electrolyte levels.
Another 2014 peer-reviewed publication concluded “Concerns regarding unwanted fluid loss associated with caffeine consumption are unwarranted particularly when ingestion precedes exercise.”
Science is about facts, supported by evidence. As much as we may emotionally wish to demonize a coffee addiction, the science shows that it’s not going to pose much risk, either through water loss or electrolyte loss… as long as we try to keep it under 15 cups per day.