Is Carbonation Bad for Kidney Stones?

Carbonation on its own does not appear to increase kidney stone risk. The carbon dioxide gas that makes water fizzy produces a weak acid (carbonic acid) that your body neutralizes quickly, and no peer-reviewed study has linked plain carbonated water to stone formation. The trouble starts with what often accompanies those bubbles: sugar, phosphoric acid, and highly variable mineral loads. Understanding which carbonated drinks matter, and why, is more useful than worrying about the fizz itself.

What Happens When You Drink Carbonated Water

When carbon dioxide dissolves in water, it forms carbonic acid, which is why sparkling water has a slightly tangy taste and a pH around 3 to 4 in the bottle. That sounds aggressive compared to plain water’s neutral pH of about 7, but the acid is extremely weak and short-lived. Once you swallow it, your body’s buffering systems in the blood and kidneys neutralize it rapidly. Carbonic acid breaks back down into CO₂ (which you partly exhale) and water. This is nothing like the sustained acid load you get from, say, a high-protein diet or a drink loaded with phosphoric acid.

One study looking at what carbonated water does inside you found that it didn’t change how fast your stomach empties food or liquid, though it did shift where the meal sits within the stomach temporarily.¹ In other words, the carbonation is mostly a physical sensation, not a lasting chemical event. There’s no mechanism by which the CO₂ in sparkling water would meaningfully alter urine chemistry in a direction that promotes stones.

Sugar-Sweetened Sodas Are a Different Story

The evidence against sugary carbonated drinks, on the other hand, is fairly convincing. A large prospective study drawing on three major cohorts found that people who drank the most sugar-sweetened cola had roughly a 23 percent higher risk of developing kidney stones compared with those who drank the least. For sugar-sweetened noncola sodas, that number rose to about 33 percent.² Those are not trivial increases, and the trend held after adjusting for overall fluid intake, meaning it wasn’t simply that soda drinkers were less hydrated.

The culprit behind sugary drinks is primarily fructose. When your body processes fructose, it raises blood uric acid levels and increases urine oxalate, while lowering urinary pH and magnesium. Each of those shifts nudges your urine toward a more stone-friendly environment. A study measuring these effects directly found that fructose ingestion significantly raised serum uric acid, increased urine oxalate, and dropped both urinary pH and magnesium.³ So the sugar, not the bubbles, is driving the risk.

The Phosphoric Acid Problem in Colas

Cola-style drinks have an additional issue that non-cola sodas don’t: phosphoric acid. This is the ingredient that gives cola its distinctive sharp tang, and it’s a stronger, more sustained acid than the carbonic acid from fizz. Phosphoric acid has been specifically associated with urinary changes that promote kidney stone formation.⁴ The acid load from phosphoric acid may contribute to calcium loss in the urine; research has shown that as your body excretes more net acid through the kidneys, urinary calcium goes up because the kidneys reabsorb less of it.⁵

This matters because calcium oxalate stones are the most common type, and extra calcium floating around in your urine is one of the conditions that encourages them to crystallize. The phosphoric acid effect is separate from, and additive to, the fructose effect. A regular cola delivers both: sugar that raises oxalate and uric acid, and phosphoric acid that may increase urinary calcium. That double hit helps explain why cola consistently shows up as a risk factor in population studies.

What About Diet Sodas

Removing the sugar removes the largest driver of risk. A study comparing the urinary stone risk profiles of people drinking caffeine-free Diet Coke and a citrus diet soda (Fresca) against those drinking a bottled still water found no increased risk and no benefit from either diet soda compared with the water.⁶ That’s a useful finding because it suggests the carbonation itself and the artificial sweeteners in those products are essentially neutral for stone formation.

The picture for diet sodas is not entirely reassuring, however. The same large cohort study that flagged sugar-sweetened drinks also found a marginally significant higher risk of stones for artificially sweetened noncola beverages.² “Marginally significant” is researcher-speak for right on the edge of being a real finding, so it’s worth noting without overstating. One possibility is that people who drink a lot of diet soda may have other dietary or metabolic patterns that contribute to stone risk, and the drink itself may not be the cause. Another possibility is that the phosphoric acid in diet colas still exerts a small effect, even without sugar alongside it. The research isn’t settled enough to say diet soda is risk-free, but the evidence is far weaker than for sugar-sweetened versions.

Sparkling Mineral Water Can Actually Help

Here’s where the story gets counterintuitive. Some types of carbonated water appear to be protective against kidney stones, not harmful. A randomized controlled trial had calcium oxalate stone formers drink either a bicarbonate-rich mineral water or plain water for 12 weeks. The mineral water group produced significantly more urine per day (an average of about 644 milliliters more), had higher urinary magnesium, higher urinary pH, and a sustained increase in urinary citrate. All of those changes move urine chemistry away from stone formation.⁷

Citrate is one of the body’s natural defenses against calcium-based stones. It binds to calcium in the urine, keeping it in solution rather than allowing it to crystallize. Higher urinary pH also discourages certain types of stone formation, particularly uric acid stones, which form more readily in acidic urine. And greater urine volume simply dilutes everything, making crystals less likely to nucleate. The fact that the mineral water group showed these benefits while the plain water group showed no significant change in citrate suggests the minerals themselves, particularly the bicarbonate, were doing additional work beyond mere hydration.

The Mineral Content of Sparkling Water Varies Enormously

Not all sparkling water is created equal, and this is where things get practical. An analysis of 126 sparkling water brands across ten European countries found enormous variation in mineral content. Sodium levels ranged from about 3 milligrams per liter to 63, and sulfate levels from 6 to 263 milligrams per liter. Calcium levels were especially variable, with some Swiss brands reaching nearly 582 milligrams per liter. The researchers concluded that patients with kidney stone disease should be aware that mineral content may influence stone formation, given how much it varies between brands.⁸

Why does this matter? If you’re prone to calcium oxalate stones, drinking a sparkling water with very high calcium might seem worrying, but the relationship between dietary calcium and stone risk is more nuanced than “more calcium equals more stones.” In fact, adequate dietary calcium tends to bind oxalate in the gut, preventing it from being absorbed and reaching the kidneys. The problem is more about getting calcium in isolation, without food, at extreme doses. On the other hand, high sodium intake genuinely increases urinary calcium excretion, so a sparkling water brand with very high sodium could work against you if you’re already eating a lot of salt.

The practical takeaway is to check labels. If you’re a stone former choosing between sparkling waters, look for brands that are lower in sodium and higher in bicarbonate. The bicarbonate acts as a natural alkalinizing agent, nudging your urine toward a less acidic pH, which is what the mineral water trial demonstrated was beneficial.

Caffeine Adds Another Wrinkle

Many carbonated drinks, from cola to energy drinks to sparkling teas, contain caffeine, and caffeine has its own relationship with stone risk. The evidence is mixed enough to be genuinely interesting. Caffeine acts as a mild diuretic, increasing urine output, which would seem protective since dilute urine is less likely to form crystals. At the same time, caffeine may slightly increase certain stone risk markers in urine. Despite that, three large cohort studies have suggested a preventive role for caffeine in kidney stone disease.⁹

The explanation might be that the extra urine volume from caffeine’s diuretic effect more than compensates for the slight bump in risk markers. Or it might be that coffee and tea drinkers (the main caffeine sources in those cohorts) have other dietary habits that are protective. Either way, the caffeine in a carbonated beverage is probably not the component you need to worry about regarding stones. It’s the sugar and the phosphoric acid that deserve your attention.

How Different Stone Types Change the Equation

Most of this discussion applies to calcium oxalate stones, which account for the majority of kidney stones. But the picture shifts if you form a different type. Uric acid stones, the second most common variety, form primarily when urine is too acidic. For uric acid stone formers, anything that raises urinary pH is protective, which means bicarbonate-rich sparkling water could be especially helpful. On the flip side, the acid load from phosphoric acid in cola is particularly counterproductive for these patients.

Struvite stones, which are caused by certain urinary tract infections, and cystine stones, which are driven by a genetic condition, operate by different mechanisms entirely. Neither is meaningfully influenced by whether your water has bubbles. If you form struvite or cystine stones, the choice between still and sparkling water is genuinely irrelevant to your stone prevention plan. The conversation about carbonation and stones is really a conversation about calcium oxalate and uric acid stones, which together make up the vast majority of cases.

Putting It Into Practice

If you enjoy sparkling water and have a history of kidney stones, there’s no reason to give it up. The carbonation itself is not the issue. What matters is the rest of the ingredient list. A few guidelines that emerge from the evidence:

Plain sparkling water is fine. No study has shown that carbonation alone increases stone risk. If you drink more total fluid because you prefer the fizz, that’s a net positive since higher urine volume is one of the best-established ways to prevent stones.
Sugar-sweetened sodas are clearly harmful. The combination of fructose, and in colas phosphoric acid, shifts urine chemistry in multiple ways that favor stone formation. Cutting these is one of the more straightforward dietary changes a stone former can make.
Bicarbonate-rich mineral water may actively help. Look for brands that list bicarbonate on the label and have moderate to low sodium. These have been shown to raise urine pH, increase citrate, and boost urine volume in stone formers.
Check the sodium. Some sparkling waters have sodium levels that start to add up if you’re drinking several bottles a day. High sodium intake increases urinary calcium excretion, which is exactly what stone formers are trying to avoid.
Diet sodas fall in the middle. They lack sugar, which removes the biggest risk factor, but some contain phosphoric acid and the population-level evidence is ambiguous enough that moderation is reasonable.

Why the Confusion Persists

Part of the reason people worry about carbonation and kidney stones is that “soda” and “sparkling water” get lumped together in everyday conversation. When a study says soda increases kidney stone risk, many people hear “carbonated drinks increase kidney stone risk” and assume the fizz is the problem. But the studies that find increased risk are almost always looking at sweetened beverages, not plain carbonated water. The 23 to 33 percent elevated risk in the large cohort study was specifically for sugar-sweetened drinks.² Plain sparkling water wasn’t implicated.

Another source of confusion is the assumption that because carbonated water is slightly acidic in the bottle, it must make your urine more acidic. Your body doesn’t work that way. The weak carbonic acid is buffered almost immediately, and your kidneys regulate urine pH based on your overall dietary acid load, not the pH of any single drink. A glass of orange juice is more acidic than sparkling water, and nobody worries about its effect on kidney stone chemistry (citrus juice is actually protective, because it supplies citrate).

The final piece of the puzzle is that the mineral content of sparkling water varies so much between brands that blanket advice is almost impossible to give. A sparkling water from one region might be extremely low in minerals, essentially identical to still tap water with bubbles, while another might deliver substantial doses of calcium, magnesium, sodium, and bicarbonate in every glass.⁸ Telling someone to “drink sparkling water” or “avoid sparkling water” without specifying which type is a bit like telling someone to “eat fish” without distinguishing between sardines and swordfish. The details matter far more than the broad category.

When Sparkling Water Replaces Something Worse

One underappreciated angle is what sparkling water displaces in your diet. If switching to flavored sparkling water means you stop drinking two cans of regular soda a day, the net effect on your stone risk is strongly positive. You’ve eliminated the fructose and possibly the phosphoric acid while maintaining or increasing your fluid intake. Many people find flat water boring and struggle to drink enough of it; if carbonation makes you drink more, the resulting increase in urine volume is among the most effective defenses against stone recurrence. Urologists consistently rank fluid intake at the top of their prevention recommendations, and any form of water that helps you hit a higher daily volume is working in your favor.

Conversely, if someone replaces plain water with a high-sodium sparkling mineral water and drinks several liters a day, the added sodium could theoretically tip the balance in the wrong direction. This is an edge case, but it’s the kind of scenario where paying attention to labels pays off. Most people drinking a bottle or two of sparkling water daily alongside a normal diet will see no meaningful difference in their stone risk compared with still water. The carbonation is, for all practical purposes, innocent.

1
PubMed. Effect of carbonated water on gastric emptying and intragastric meal distribution
2
PubMed Central. Soda and other beverages and the risk of kidney stones
3
PubMed Central. Fructose increases risk for kidney stones: potential role in metabolic syndrome and heat stress
4
PubMed Central. Carbonated Beverages and Chronic Kidney Disease
5
PubMed. Relationship between urinary calcium and net acid excretion as determined by dietary protein and potassium: a review
6
PubMed Central. Effect of Soda Consumption on Urinary Stone Risk Parameters
7
PubMed. The effects of drinking bicarbonate-rich mineral water in calcium oxalate stone formers: an open label prospective randomized controlled study in an Asian cohort
8
Central European Journal of Urology. Variations in the mineral content of bottled ‘carbonated or sparkling’ water across Europe: a comparison of 126 brands across 10 countries
9
Advances in Nutrition. Caffeine in Kidney Stone Disease: Risk or Benefit?