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Why Is Cranberry Juice Good For UTIs?

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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.

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Big Questions
Why Is Soda Measured in Liters?
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Never a nation to fall in line, America is one of the few countries to resist the metric system. We stubbornly measure distance in miles and weight in pounds. So what’s with those two-liter bottles of soda?

First, a clarification: Soda is far from the only substance we measure in metric units. Heck, it’s not even the only beverage. Wine, liquor, and bottled water are sold by the milliliter. The healthcare field is all about metric units, too, from cholesterol levels to prescription, over-the-counter, and supplement dosages. We run 5-kilometer races, ride on 215-millimeter tires, and use 8-millimeter cameras, or at least we used to.

In most other things, we determinedly cling to our imperial measurements. Attempts to convince Americans to join the rest of the metric-measuring world have been met with great resistance.

Ken Butcher of the National Institute of Science and Technology has been working with the government’s tiny Metric Program for years. Speaking to Mental Floss back in 2013, Butcher explained that we’re so entrenched in our way of doing things that switching measurement systems now would be both chaotic and expensive.

"If we were going to start a new country all with the metric system, it would be easy," he said. "But when you have to go in and change almost everything that touches people’s everyday life and their physical and mental experience, their education, and then you take that away from them—it can be scary."

Here and there, though, when it’s convenient, we have been willing to budge. The soda bottle is a good example. Until 1970, all soft drinks in the U.S. were sold in fluid ounces and gallons, mostly in glass bottles. Then the plastic polyethylene terephthalate (PET) bottle came along, and soft drink makers decided it was time for a product redesign.

The redesign process coincided with two key factors: a short-lived wave of government interest in going metric, and the burgeoning environmental movement.

The folks at PepsiCo decided to meld all three into its exciting new vessel: a lightweight, cheap, recyclable, metric bottle, with built-in fins so it could stand up on supermarket shelves. Two liters: the soda size of the future.

The two-liter bottle took off. The rest of the soft drink world had no choice but to get on board. And voila: liters of cola for all.

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

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Big Questions
Where Is the Hottest Place on Earth?
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The summer of 2017 will go down as an endurance test of sorts for the people of Phoenix, Arizona. The National Weather Service issued an extreme heat warning, and planes were grounded as a result of temperatures exceeding 120 degrees. (Heat affects air density, which in turn affects a plane’s lift.)

Despite those dire measures, Phoenix is not the hottest place on Earth. And it’s not even close.

That dubious honor was bestowed on the Lut Desert in Iran in 2005, when land temperatures were recorded at a staggering 159.3 degrees Fahrenheit. The remote area was off the grid—literally—for many years until satellites began to measure temperatures in areas that were either not well trafficked on foot or not measured with the proper instruments. Lut also measured record temperatures in 2004, 2006, 2007, and 2009.

Before satellites registered Lut as a contender, one of the hottest areas on Earth was thought to be El Azizia, Libya, where a 1922 measurement of 136 degrees stood as a record for decades. (Winds blowing from the nearby Sahara Desert contributed to the oppressive heat.)

While the World Meteorological Organization (WMO) acknowledged this reading as the hottest on record for years, they later declared that instrumentation problems and other concerns led to new doubts about the accuracy.

Naturally, declaring the hottest place on Earth might be about more than just a single isolated reading. If it’s consistency we’re after, then the appropriately-named Death Valley in California, where temperatures are consistently 90 degrees or above for roughly half the year and at least 100 degrees for 140 days annually, has to be a contender. A blistering temperature of 134 degrees was recorded there in 1913.

Both Death Valley and Libya were measured using air temperature readings, while Lut was taken from a land reading, making all three pretty valid contenders. These are not urban areas, and paving the hottest place on Earth with sidewalks would be a very, very bad idea. Temperatures as low as 95 degrees can cause blacktop and pavement to reach skin-scorching temperatures of 141 degrees.

There are always additional factors to consider beyond a temperature number, however. In 2015, Bandar Mahshahr in Iran recorded temperatures of 115 degrees but a heat index—what it feels like outside when accounting for significant humidity—of an astounding 163 degrees. That thought might be one of the few things able to cool Phoenix residents off.

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

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