Here’s How Caffeine Affects Your Urine

A mild diuretic, caffeine causes your kidneys to flush extra sodium and water from your body.
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If caffeine and coffee keep you going, but you worry about the potential diuretic effect, you're in luck. While caffeine is a mild diuretic, experts agree that it does not cause your body to excrete more fluid than it needs — and its effects are short-lived.

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Here's what to know about the effects of caffeine on urine.

Read more:What Really Happens to Your Body When You Have Caffeine

Caffeine's Diuretic Mechanism

The U.S. National Library of Medicine confirms what all fans of caffeinated coffee, tea, soda and cocoa likely already know: Caffeine is a diuretic.

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"A diuretic is any substance that may cause the need to urinate," says Russell de Souza, ScD, RD, registered dietitian, nutritional epidemiologist and associate professor at McMaster University in Hamilton, Ontario, Canada. "And caffeine is a mild diuretic," he says, "which means that it causes your kidneys to flush extra sodium and water from the body through urine."

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In addition to being mild, a caffeine-triggered increase in urination is typically short-lived, according to the National Kidney Foundation.

Why? Because even though "it can take up to 10 hours for caffeine to completely clear your system," de Souza says, "caffeine is rapidly and completely absorbed, with 99 percent being absorbed within 45 minutes of ingestion."

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Caffeine's Effect on Urine Output

So from a urinary system perspective, is caffeine a friend or foe?

One possible concern is overactive bladder. Yet the research to date is mixed.

A September 2019 ​Lower Urinary Tract Symptoms​ study notes that reducing caffeine intake is considered to be a first-line treatment for anyone with an overactive bladder (OAB), a chronic, sudden and uncontrollable urge to urinate, according to the Mayo Clinic.

And a small July 2014 study of women with OAB in the ​Journal of Wound, Ostomy, and Continence Nursing​ found that when caffeinated drinks were replaced with decaf substitutes, urinary frequency and urgency fell.

But other studies are less decisive. An April 2017 meta-analysis in ​Neurourology and Urodynamics​ concluded that while some research does suggest that caffeine reduction may help with bladder control, other studies do not — and more research is needed.

Similarly, a December 2015 review in the ​Cochrane Database of Systematic Reviews​ found there's insufficient evidence that reducing caffeine intake has any effect on incontinence. And an October 2016 review in ​BMC Urology​ that compared people who never drank caffeinated coffee versus those who regularly did found no link between caffeine and risk of incontinence.

That may be because, as de Souza says, on the scale of diuretics, it's a mild one.

Caffeine and Dehydration

A January 2014 study in ​PLOS One​ found that, while relatively high caffeine intake can temporarily trigger increased urination, low to moderate amounts of caffeine do not.

The study specifically addressed the question of caffeine-induced dehydration risk among healthy men, concluding that in moderation — meaning 4 milligrams of caffeine for every kilogram of body weight per day — caffeinated coffee does not trigger the kind of excretion levels that might lead to dehydration. (According to the Cleveland Clinic, the average American adult takes in about 200 milligrams of caffeine per day.)

"Caffeinated drinks — most commonly tea and coffee — don't appear to increase the risk of dehydration," de Souza says.

In fact, "studies show that drinking even large doses of caffeinated beverages don't appear to make you pee out any more fluid from your body over and above what you drank," he says.

In other words, "your body is able to absorb as much fluid as it needs, and expel the rest," he says.

Caffeine and Urine Color

And for those who are curious, de Souza says caffeine also "probably won't make your urine any darker or lighter."

In some cases, "if you are drinking a lot of coffee or tea," he says, urine color may be a shade lighter. "But I don't think it's a major cause for concern, unless someone's physician has a reason to suspect otherwise."

Read more:How Bad Is It Really to Drink More Than the Daily Recommended Amount of Coffee?

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