Sparkling Water: Teeth, Stomach, Bones and Bloating — Is It Harmful?

Carbonation means dissolving carbon dioxide (CO2) in water. Some of the molecules react with the water to form carbonic acid, which lowers the drink’s pH: sparkling water is therefore clearly more acidic than still, and its pH usually sits a few units below neutral. That is where the intuition comes from that, since acids dissolve enamel, water with bubbles must be dangerous.

The intuition overlooks two things. First, carbonic acid is a weak and unstable acid: it is exhaled as a gas and escapes quickly once the bottle is opened. Second, how erosive a drink is depends not only on pH but also on its so-called titratable acidity (how much base must be added to neutralise it) and on its content of calcium, magnesium and other ions, which can inhibit enamel dissolution. In cola-type drinks the manufacturer has added strong acids (phosphoric, citric), a completely different mechanism from mineral water with CO2.

In practice three different things are sold as ‘sparkling water’: mineral water naturally or artificially saturated with CO2, soda-maker water (ordinary water with CO2), and flavoured waters with aromas and added acids. For teeth and for the stomach these are not the same, and this difference settles most of the disputed questions.

The best-cited laboratory study on this question compared a range of still and sparkling mineral waters and soft drinks in dissolution tests, on extracted human teeth and hydroxyapatite powder, the main component of enamel. The results were clear: dissolution in all mineral waters was very low, and for several still waters undetectable.

This study has limits, however: it is a laboratory (in vitro) study that does not account for saliva, tooth brushing or daily drinking habits. It also says nothing about how often and for how long teeth are exposed. Even so, it fits the chemical intuition: plain sparkling water is acidic but has low titratable acidity and usually contains calcium, which protects against dissolution.

The practical conclusions are simple. Plain sparkling water is not the main suspect in enamel erosion, but frequent, prolonged sipping of acidic drinks, including flavoured ones, calls for caution. We cover caries prevention and oral health in our material on xylitol and dental health.

Contrary to popular belief, sparkling water is not ‘heavy on the stomach’ for everyone. In a small, double-blind randomised trial by Italian authors, 21 patients with functional dyspepsia and secondary constipation drank either sparkling water (10 people) or tap water (11 people) for about 15 days. The dyspepsia score fell in the sparkling-water group from 7.9 to 5.4 points, while in the control group it stayed unchanged (9.7 and 9.9). The constipation score also fell significantly after sparkling water (from 16.0 to 12.1) but not after tap water.

Too much should not be read into this: the study covered only 21 people, lasted two weeks and involved a selected group of patients with specific symptoms. It does not show that sparkling water will help everyone, or that it is safe for everyone. It does show that the general view of its harmfulness to the digestive system has no universal confirmation.

On the other hand, carbon dioxide in the stomach and gut is a gas. In sensitive people, with bloating, irritable bowel syndrome or a tendency to belch, water full of bubbles is sometimes a cause of discomfort. We found no controlled trials that directly and reliably assess sparkling water in irritable bowel syndrome, so advice here rests on mechanism and clinical practice, not on RCTs. If bloating appears after sparkling water, the simplest test is a few days’ break and a comparison. We cover the causes of bloating in the article on bloating after eating.

Carbonated drinks can weaken the lower oesophageal sphincter, the valve between the oesophagus and the stomach. In a manometry study of 18 healthy volunteers, 200 ml of chilled cola lowered sphincter pressure from a median of 40.5 to 18.5 mmHg and increased the number of transient sphincter relaxations (median 10.5 versus 1 after water), whereas still water did not have this effect. In another study of 9 healthy volunteers, carbonated drinks reduced sphincter parameters by 30 to 50% for about 20 minutes, while tap water did not.

It must be said honestly that both manometry studies used carbonated drinks (cola in one of them), not plain mineral water with CO2. We found no controlled trials assessing plain sparkling water in reflux on its own, so it is unknown how much of the effect is due to the gas and how much to caffeine, acids and the drink’s composition. What is known is that distension of the stomach with gas can promote belching and regurgitation. People with symptomatic reflux can therefore try replacing sparkling with still water for a few weeks and watch their symptoms. An interesting aside is that some bicarbonate-rich mineral waters have been studied as a way to ease heartburn; we write about that in the article on alkaline water.

The belief that carbonated drinks ‘leach calcium from bones’ comes from observational studies. The most cited is the Framingham Osteoporosis Study analysis of 1413 women and 1125 men, in which bone mineral density was measured by DXA and diet assessed with a food frequency questionnaire. After adjusting for age, BMI, activity, smoking, alcohol and calcium and vitamin D intake, cola consumption was associated with lower bone density at every hip site examined, but not in the spine, in women but not in men.

In the general population plain sparkling water is safe, but a few groups should be more careful. People with reflux or frequent heartburn may notice worse symptoms after carbonated drinks. People with irritable bowel syndrome or a tendency to bloating often report discomfort after water with bubbles. People at higher risk of enamel erosion (dry mouth, reflux, frequent sipping of acidic drinks) should avoid flavoured waters and not sip any acidic drink throughout the day. People on a sodium-restricted diet should check the sodium content on the label of mineral water.

If you like sparkling water, there is no reason to give it up just because it has bubbles. If, however, you have reflux, bloating or a tendency to enamel erosion, it is worth checking on yourself whether still water makes a difference, because that is the cheapest and most reliable test.

Sparkling water has fallen victim to overgeneralisation: bubbles are associated with cola, so everything harmful in cola is attributed to water. The data show that plain mineral water with CO2 is, in most cases, a safe alternative to sweetened drinks, and the real problems are the added acids in flavoured waters and the individual sensitivity of the stomach and oesophagus. It is therefore worth listening to your own body rather than fearing bubbles on principle.