After drinking a cup of coffee, you might feel that your mouth is a bit dry, or that you have a sudden need to take a bathroom break. And that’s led to the following conventional wisdom: coffee is a diuretic.
In layman’s terms, that means that drinking coffee causes a net loss of bodily fluids. Drink too much coffee, the thinking goes, and you’ll risk dehydration because you are losing more fluids than you are putting in.
However, speculation about coffee being a diuretic is just that – speculation. The medical evidence conclusively showing that coffee is a diuretic is surprisingly limited. In general, coffee only seems to have diuretic effects when it’s consumed in large amounts – at least 500-600 milligrams (mg) of caffeine per day.
The culprit in coffee – if you want to call it that – is the caffeine. This is a stimulant, and that’s why some people get headaches, the jitters or a faster heart rate after drinking coffee – the caffeine is going to work on your body’s metabolism. It can constrict the body’s blood vessels, raising your blood pressure. And it can cause insomnia and anxiety, so you probably don’t want to drink coffee before going to bed.
If you enjoy the taste of it or the experience of hanging out at a coffee ship, but don’t want all the changes to your body’s metabolism, there’s always decaf. You may not get the same clarity and alertness that caffeine gives many coffee drinkers, but you also won’t get the caffeine jitters.
So how many cups is that?
Well, a standard 8 oz. cup of coffee – the kind that you might brew using a home coffee machine – has 150 milligrams of caffeine. And a 12 oz. “tall” cup of Starbucks coffee has about 240 milligrams. A latte, in comparison, is relatively weak, with only about 90 milligrams.
In other words, you’d have to drink about 4 regular coffees, 3 Starbucks coffees or 6 lattes for coffee to experience any diuretic effects. If you’re just grabbing one cup of coffee in the morning before heading off to school or work, you’re all clear.
But in terms of your body’s fluid balance, drinking decaf may have very little real effect unless you tend to drink prodigious amounts of coffee each day. In scientific studies, researchers have found that the urge to take a bathroom break only shows up at the 360 mg level. That means you’re not losing any extra fluids as long as you’re only consuming a cup of coffee at a time.
However, if you’re still not convinced that coffee is not a diuretic, you do have other options beyond just decaf. One of them is switching over to tea. It’s not so much that tea is better for you — it’s just that it contains more water than coffee. So your body is getting more water intake with every cup. Moreover, the level of caffeine in tea is much smaller than in coffee, so your body’s metabolism isn’t impacted as much.
Thus, if you’re a longtime coffee drinker, no worries. At best, coffee is a mild diuretic. As with most substances that you put into your body, small to moderate amounts won’t have much of an impact.