Why Everything You’ve Heard About Coffee Dehydrating You Is Wrong

Why Everything You’ve Heard About Coffee Dehydrating You Is Wrong

Is Coffee Dehydrating? Turns Out... It’s Not!

You've probably heard that coffee is dehydrating — but research tells a different story.

A recent study measured the effects of various beverages on hydration, urine production, and electrolyte balance. The findings? There was no significant difference between tea, coffee, soda, diet soda, and water. All were equally hydrating.

They also found no difference in urine production between caffeinated beverages and water. While the tea and coffee groups did lose slightly more sodium in their urine compared to the water group, it wasn’t enough to impact overall hydration.

Interestingly, some drinks actually hydrate better than water, including orange juice, whole milk, semi-skimmed milk, and oral rehydration solutions.

But wait, isn’t caffeine a diuretic?

Technically, yes — but only at high doses. An average 8 oz cup of coffee contains about 95 mg of caffeine, which is a relatively small amount.

Research showed that caffeine can increase urine output at a dose of 6 mg per kilogram of body weight, but not at 3 mg per kilogram.

To put it in perspective:
For me personally, I would need to consume 654 mg of caffeine — that’s about 6.8 cups of coffee — in one sitting to experience a measurable diuretic effect.

How to Calculate It for Yourself

If you want to know exactly how much caffeine it would take for coffee to become less hydrating for you, here’s the simple formula:

Step 1: Find your weight in kilograms.

  • Take your weight in pounds and divide by 2.2.

Step 2: Multiply by 6.

  • This gives you the caffeine threshold in milligrams.

Step 3: Calculate how many cups of coffee that equals.

  • Divide that caffeine number by 95 (since one 8oz cup of coffee has about 95mg of caffeine).

Example:
Let’s say you weigh 180 pounds.

  • 180 ÷ 2.2 = 81.8 kilograms

  • 81.8 × 6 = 490.8 mg of caffeine

  • 490.8 ÷ 95 ≈ 5.2 cups of coffee

You would need to drink about 5.2 cups of coffee at once to reach the point where coffee would be slightly less hydrating — and even then, it's not dehydrating.

The Bottom Line

Unless you’re pounding 5–7 cups of coffee in one sitting, your coffee is just as hydrating as water.

Drink up and enjoy.

Quick Highlights:

  • Coffee, tea, and soda hydrate about the same as water.

  • Caffeine only acts as a diuretic at high doses (6mg/kg bodyweight).

  • Milk and orange juice hydrate even better than water.

  • Your daily coffee habit is helping, not hurting, your hydration.

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