Getty Images
Getty Images

Why Is Cranberry Juice Good For UTIs?

Getty Images
Getty Images

A mental_floss staffer who shall remain nameless asks, “Why is cranberry juice good for treating UTIs? I will not tell you why this question had been on my mind.”

Bacterial infections in the urinary tract and its organs are pretty common, especially in adult women, and more than seven million cases are reported by doctors every year. Among women who get one, about a third will experience them recurrently.

A popular folk remedy for the infections is cranberry juice. How the juice relieves UTIs, and even if it actually does help, isn’t entirely clear. Research on its effectiveness for UTI prevention has produced mixed results, and studies assessing the use of cranberry juice in UTI treatment are few. The strongest evidence available for prevention is among adult women with previous UTIs. In this group, results repeatedly show about a 50% reduction in disease recurrence with regular juice consumption. In elderly and pediatric patients, and some patients with bladder problems, the effect is less pronounced.

A caveat made in many of the prevention studies is that the cranberry juice’s effects seem to be dose-dependent, and that the amount a person would need to drink daily to have a real preventative effect is more than what most people are willing to drink. In some studies, as many as half of the participants withdrew before the studies' completion, suggesting that prolonged, regular guzzling of cranberry juice is too much to bear, either because of stomach aches, the calorie load, or adverse interactions between the juice and certain medications.

Overall, the evidence suggests that cranberry juice helps prevent UTIs. But how?

The Compound Equation

Cranberries contain quinic, malic, and citric acids, and for a long time researchers thought that the acidity of this mix had a bacteriostatic effect that kept bacteria from reproducing and gave cranberry juice its usefulness. Further studies showed that the amount of acid in the juice and the low amounts that people would tolerate drinking weren’t enough for the acid to do much good, though. More recent research suggests that the juice’s real benefit is that certain compounds in it keep bacteria from setting up shop in the urinary tract.

E. coli and other common UTI-causing bacteria have hairlike appendages called fimbria that they use to adhere to the walls of the urinary tract. A few different studies have found that two compounds in cranberries—fructose and proanthocyanidin—inhibit bacteria’s fimbria from sticking to anything, preventing the bacteria from colonizing and multiplying. The compounds' antiadherent effects start within two hours after someone drinks cranberry juice and persist for up to 10 hours after ingestion, keeping an infection from taking hold.

Other research has found that cranberry juice additionally alters and increases certain thermodynamic properties of bacteria in the urinary tract—including the amount of energy that that they have to expend before they can attach to tissue—creating an energy barrier that they can’t overcome, and therefore preventing them from latching on. If the bacteria can’t stick to the walls of the urinary tract, then they’re vulnerable to being flushed out and away by urine.

Why You Should Never Take Your Shoes Off On an Airplane

What should be worn during takeoff?

Tony Luna:

If you are a frequent flyer, you may often notice that some passengers like to kick off their shoes the moment they've settled down into their seats.

As an ex-flight attendant, I'm here to tell you that it is a dangerous thing to do. Why?

Besides stinking up the whole cabin, footwear is essential during an airplane emergency, even though it is not part of the flight safety information.

During an emergency, all sorts of debris and unpleasant ground surfaces will block your way toward the exit, as well as outside the aircraft. If your feet aren't properly covered, you'll have a hard time making your way to safety.

Imagine destroying your bare feet as you run down the aisle covered with broken glass, fires, and metal shards. Kind of like John McClane in Die Hard, but worse. Ouch!

Bruce Willis stars in 'Die Hard' (1988)
20th Century Fox Home Entertainment

A mere couple of seconds delay during an emergency evacuation can be a matter of life and death, especially in an enclosed environment. Not to mention the entire aircraft will likely be engulfed in panic and chaos.

So, the next time you go on a plane trip, please keep your shoes on during takeoff, even if it is uncomfortable.

You can slip on a pair of bathroom slippers if you really need to let your toes breathe. They're pretty useless in a real emergency evacuation, but at least they're better than going barefoot.

This post originally appeared on Quora. Click here to view.

Big Questions
Where Should You Place the Apostrophe in President's Day?

Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" infers that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the nearly 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.

Wikimedia Commons // Public Domain

Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington/Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King, Jr., and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at


More from mental floss studios