You're sitting at your desk when you hear the familiar pop of a pull tab breaking open a can one cubicle over. Ah, the friendly office seltzer water addict is at it again. All day he knocks back can after can of the stuff like it's Bud Light and he's competing against his frat brothers in a case race. But what's going on in his gut as he guzzles all that sparkling water? Should he—at least occasionally—give his stomach a break from the carbonated stuff?
Your coworker is part of a committed cult: The seltzer water market is booming—sparkling water sales grew 15.5 percent from 2015 to 2016, making it the fastest-growing segment in the bottled water market, according to Mintel's 2017 report on the industry. The research firm expects its sales to grow a whopping 91.8 percent by 2021, making it worth $4.5 billion. Regular tap water falls flat because it's missing a key ingredient. "Seltzer water is essentially flat water with carbon dioxide infused into it under pressure," says Scott Tomar, professor and chair of the department of community dentistry and behavioral science at the University of Florida.
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But is seltzer water healthier than regular water? It's complicated. The resulting carbonation means two things: First, sparkling waters have a lower potential of Hydrogen (pH) than flat waters, which makes them more acidic. Researchers from the University of Alabama at Birmingham analyzed 379 drinks and found that pH levels of two seltzers clocked in at 4.96 and 5.25. But that's far from the risky 2 to 4 range—where most sodas and fruit juices fall—which puts you at risk for tooth erosion.
Your body also needs to do more work to process carbonated water. "The CO2 bubbles have to be absorbed through the gastric walls first," says Gina Sweat, a registered dietician at the Cleveland Clinic. "Flat water just doesn't need to go through that process."
The Worst That Can Happen
If your friend has any conditions that affect his digestive tract—like irritable bowel syndrome, irritable bowel disease, colitis, or gastritis—seltzer water's acidity can exacerbate his condition by irritating the lining in the stomach and intestines, Sweat says.
As for whether or not seltzer water causes tooth decay, the concerns aren't without merit: Flavored seltzers are also more acidic than people think. An analysis published in the International Journal of Pediatric Dentistry found their pH levels fell between 2.74 and 3.34, well within the danger zone for acidity.
If you're worried, just take a glance at your teeth: "The white outer layer is dental enamel, and its primary function is to protect the underlying tooth structure," Tomar says. A healthy person's saliva neutralizes acid—but drinking too many acidic drinks throws off that balance and erodes the enamel, subjecting the soft inner part of your teeth to sensitivity, discoloration, and cracking.
What Will Probably Happen
Your coworker is probably gassy and under-hydrated. "[Seltzer water] increases gas in the GI tract, so it can cause bloating, stomach cramps, and stomach distension," Sweat says. The bubbles make you feel full faster, she says, so your water intake might fall short at the end of the day.
He may also be overfed: People had three times as much of the hunger hormone ghrelin in their systems after drinking a fizzy drink than they did after drinking a degassed flat soda, and six times as much as they did after drinking flat water, according to a study published this year in Obesity Research and Clinical Practice.
What Your Friend Should Do
Tell your friend to maybe cool it a bit with the flavored seltzers, since the added acidity could rot his teeth and irritate his insides—especially if he has a digestive condition. "My first line of recommendation is always 100 percent water," Sweat says, but if you're used to the bubbles, she suggests a reasonable 70:30 flat to fizzy ratio. Read This Next: How Bad is it to Mix Booze and Painkillers?