Seltzer water, often known as carbonated water, has become a popular alternative to sugary soft drinks, but its fizziness has raised questions about its effect on kidney health. Kidney stones are hard deposits of minerals and salts that form when urine becomes highly concentrated, allowing substances like calcium oxalate or uric acid to crystallize and stick together. The public concern is whether the carbonation process changes the body’s chemistry in a way that promotes this crystallization. Understanding the composition of seltzer helps clarify its actual role in kidney stone formation.
The Chemistry of Seltzer and Kidney Stone Risk
The effervescence in seltzer is achieved by dissolving carbon dioxide gas in water under pressure, which creates a small amount of carbonic acid. This process makes the water slightly acidic, giving it a lower pH than regular tap water. However, this mild acidity is not a significant factor in promoting kidney stone formation. The body has powerful buffering systems that quickly neutralize the small amount of carbonic acid consumed. Scientific evidence shows that drinking seltzer water does not significantly alter the overall acid-base balance of the body or the acidity of the urine.
What Seltzer Does Not Contain
The safety of seltzer water is often best understood by comparing what it lacks, especially when stacked against other popular carbonated beverages. Plain seltzer is simply water and carbon dioxide, containing no added sugars or calories. This is a major advantage over sugar-sweetened sodas, which contain high levels of fructose linked to increased kidney stone risk. Seltzer also does not contain the high levels of phosphoric acid found in many dark colas. Phosphoric acid contributes to stone formation because it can alter urine composition by lowering urinary citrate, a natural inhibitor of calcium stones.
Primary Dietary Factors That Increase Kidney Stone Risk
The real drivers of kidney stone formation lie in specific dietary components that increase the concentration of stone-forming substances in the urine.
Calcium Oxalate Stones
For the most common type, calcium oxalate stones, a high intake of sodium is a major contributor. Excess sodium causes the kidneys to excrete more calcium into the urine, which then easily combines with oxalate to form crystals. Another element is excessive consumption of high-oxalate foods, such as spinach, rhubarb, nuts, and chocolate, especially if not balanced with calcium intake. When dietary calcium is too low, oxalate is more readily absorbed from the gut and excreted by the kidneys, increasing the risk of stone formation.
Uric Acid Stones
Uric acid stones, the second most common type, are primarily influenced by a high intake of animal protein. High animal protein consumption increases the overall acid load in the body and raises uric acid levels in the urine, making it more prone to crystallization.
Hydration as the Key to Prevention
The most effective strategy for preventing kidney stones is ensuring a sufficient intake of fluids every day. Kidney stones form when the urine is concentrated, which allows minerals to crystallize more easily. By drinking enough fluid, the stone-forming chemicals in the urine are diluted, significantly reducing the likelihood of crystallization. Many individuals who have a history of stones are advised to drink enough to produce at least 2 to 3 liters of urine daily. Seltzer water is an acceptable way to reach this fluid goal because it is nearly all water and does not contain the problematic ingredients of soda.