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The Bitter Truth About Coffee (or is it?)

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The Bitter Truth About Coffee (or is it?)

Yesterday, we asked you for your (health-related) views on coffee. The results were clear: if we assume the responses to be representative, we’re a large group of coffee-enthusiasts!

One subscriber who voted for “Coffee is a healthy stimulant, hydrating, and full of antioxidants” wrote:

❝Not so sure about how hydrating it is! Like most food and drink, moderation is key. More than 2 or 3 cups make me buzz! Just too much.❞

And that fine point brings us to our first potential myth:

Coffee is dehydrating: True or False?

False. With caveats…

Coffee, in whatever form we drink it, is wet. This may not come as a startling revelation, but it’s an important starting point. It’s mostly water. Water itself is not dehydrating.

Caffeine, however, is a diuretic—meaning you will tend to pee more. It achieves its diuretic effect by increasing blood flow to your kidneys, which prompts them to release more water through urination.

See: Effect of caffeine on bladder function in patients with overactive bladder symptoms

How much caffeine is required to have a diuretic effect? About 4.5 mg/kg.

What this means in practical terms: if you weigh 70kg (a little over 150lbs), 4.5×70 gives us 315.

315mg is about how much caffeine might be in six shots of espresso. We say “might” because while dosage calculations are an exact science, the actual amount in your shot of espresso can vary depending on many factors, including:

  • The kind of coffee bean
  • How and when it was roasted
  • How and when it was ground
  • The water used to make the espresso
  • The pressure and temperature of the water

…and that’s all without looking at the most obvious factor: “is the coffee decaffeinated?”

If it doesn’t contain caffeine, it’s not diuretic. Decaffeinated coffee does usually contain tiny amounts of caffeine still, but with nearer 3mg than 300mg, it’s orders of magnitude away from having a diuretic effect.

If it does contain caffeine, then the next question becomes: “and how much water?”

For example, an Americano (espresso, with hot water added to make it a long drink) will be more hydrating than a ristretto (espresso, stopped halfway through pushing, meaning it is shorter and stronger than a normal espresso).

A subscriber who voted for “Coffee messes with sleep, creates dependency, is bad for the heart and gut, and is dehydrating too” wrote:

❝Coffee causes tachycardia for me so staying away is best. People with colon cancer are urged to stay away from coffee completely.❞

These are great points! It brings us to our next potential myth:

Coffee is bad for the heart: True or False?

False… For most people.

Some people, like our subscriber above, have an adverse reaction to caffeine, such as tachycardia. An important reason (beyond basic decency) for anyone providing coffee to honor requests for decaff.

For most people, caffeine is “heart neutral”. It doesn’t provide direct benefits or cause direct harm, provided it is enjoyed in moderation.

See also: Can you overdose on caffeine?

Some quick extra notes…

That’s all we have time for in myth-busting, but it’s worth noting before we close that coffee has a lot of health benefits; we didn’t cover them today because they’re not contentious, but they are interesting nevertheless:


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