It's not just the water: these are the real risk factors for kidney stones

Stones in the kidneys do not just appear from drinking little water: they arise when urine concentrates minerals and compounds that crystallize, in people with genetic predisposition, diets with excess salt or animal proteins, obesity, metabolic diseases, infections, or certain treatments. They can form over weeks or months and cause symptoms when they block the flow of urine. The risk increases when several of these factors combine, according to health agencies and urology guidelines. ADVERTISEMENT Kidney stones, also called renal lithiasis, are solid masses that originate within the kidneys from substances present in the urine, such as calcium, oxalate, phosphate, and uric acid. The National Institute of Diabetes and Digestive and Kidney Diseases in the United States explains that the problem begins when there are too many substances capable of forming crystals or when there are a lack of compounds that prevent them from grouping. Concentrated urine is the starting point, but does not explain all cases Dehydration and low urine volume remain among the most frequent risks. When a person produces little urine, the concentrations of calcium, oxalate, phosphate, or uric acid increase, which favors supersaturation and crystal formation. ADVERTISEMENT MedlinePlus points out that the risk increases when the daily urine production drops below approximately one liter. This condition can occur due to insufficient water intake, intense sweating, exercise without fluid replenishment, or prolonged exposure to heat. The Mayo Clinic adds that living in hot and dry areas, or working in hot environments, can increase the probability of developing stones if water loss is not compensated for. But hydration alone does not determine who will have stones. The National Kidney Foundation warns that urine with little fluid and excess minerals is only part of the equation: diet, weight, diseases, and certain medications can modify urinary composition even in those who drink a reasonable amount of water. ADVERTISEMENT Salt, animal proteins, and sugars change the chemistry of the urine Diet is among the most scientifically supported modifiable factors. The National Kidney Foundation identifies the high consumption of sodium, animal proteins, and added sugars as habits associated with a greater likelihood of stone formation. Excess salt increases the excretion of calcium in the urine. This change can facilitate the appearance of oxalate or calcium phosphate stones, which are the most frequent types. Diets abundant in beef, pork, poultry, fish, and seafood can also increase the risk. These foods increase the acid load on the kidney, reduce urinary citrate, and can increase uric acid. ADVERTISEMENT Citrate acts as a natural brake on crystallization because it binds to calcium and reduces its availability to form stones. A low concentration of this substance, known as hypocitraturia, is associated with a higher risk of calcium lithiasis. A systematic review published in BMC Nephrology related high consumption of sodium, fructose, meat, animal proteins, and soft drinks to a higher incidence of stones. The same study linked obesity to a 39% increase in the risk of lithiasis. Not all dietary changes consist of restricting products. The National Kidney Foundation maintains that adequate calcium intake from food can reduce intestinal absorption of oxalate and help prevent calcium oxalate stones. ADVERTISEMENT Diets too low in calcium can have the opposite effect in predisposed individuals. With less calcium available in the intestine, more oxalate remains free to be absorbed and then excreted in the urine. Obesity, diabetes, and hypertension also increase the risk Excess weight and metabolic syndrome are associated with urine more favorable for stone formation. Insulin resistance can reduce the kidney's ability to buffer acidity, which lowers urinary pH and facilitates uric acid stones. A cohort study conducted in Iran, with more than 10 thousand adults aged 40 to 70 years, detected associations between renal lithiasis, diabetes, hypertension, fatty liver, and excess weight. ADVERTISEMENT In that analysis, people with fatty liver had 2.21 times higher risk of presenting stones. Hypertension was related to a 1.43 times higher risk and overweight, to one 1.35 times higher risk. Type 2 diabetes, obesity, and gout are especially linked to uric acid stones. In these cases, not only the amount of uric acid excreted matters: it is also decisive that the urine maintains an elevated acidity. The European Association of Urology includes metabolic syndrome among the conditions that should be taken into account when classifying the risk of recurrence and possible long-term renal damage. ADVERTISEMENT Family history and stone type change the prognosis Having had a stone before is one of the most useful indicators to anticipate another episode. European guidelines estimate that recurrence after a first stone is around 26% within five years. Family history also matters. The National Institutes of Health in the United States and MedlinePlus Genetics agree that history in close relatives reflects both hereditary susceptibility and shared environmental habits and conditions. In most people, genetic risk depends on multiple variants that interact with diet, hydration, and health status. In other patients, a specific hereditary alteration can be the central cause of the disease. ADVERTISEMENT Cystinuria, for example, causes excessive excretion of cystine in the urine. Since this amino acid is poorly soluble, it can cause recurrent stones from childhood or adolescence. Primary hyperoxaluria is another high-risk genetic disorder. In this case, the body produces very high amounts of oxalate, which favors calcium oxalate stones and mineral deposits within kidney tissue. The European Association of Urology considers those with early-onset lithiasis, frequent recurrences, family history, cystine, uric acid, brushite or struvite stones, as well as certain metabolic and anatomical diseases, to be at high risk. Digestive diseases and infections can be determining Intestinal diseases and some digestive surgeries increase the risk because they alter the absorption of fats and oxalate. MedlinePlus explains that when fats are not absorbed properly, they bind to calcium in the intestine and leave more oxalate available to enter the body. This phenomenon, called enteric hyperoxaluria, can occur in people with inflammatory bowel disease, extensive intestinal resections, or malabsorptive bariatric surgery. Chronic diarrhea adds another problem: they can cause loss of fluids and bicarbonate. This combination favors dehydration, modifies urinary pH, and reduces urinary citrate. Recurrent urinary infections can also cause stones, especially struvite stones. These form in the presence of bacteria that produce urease, such as Proteus mirabilis, capable of raising urinary pH. MedlinePlus warns that struvite stones can grow rapidly and occupy large areas of the renal collecting system. In these cases, the infection and the stone can feed each other: the stone facilitates the persistence of bacteria and the infection contributes to new mineral deposits. Some medications require medical review Certain drugs modify the chemistry of the urine or can precipitate directly in the urinary tract. The National Institutes of Health include some diuretics, calcium-containing antacids, the antiretroviral indinavir, and the anti-epileptic topiramate among them. Topiramate, also used to prevent migraines, can reduce urinary citrate and raise pH. This profile favors primarily calcium phosphate stones. High doses of vitamin C deserve attention in predisposed people, as a part is metabolized to oxalate. The Mayo Clinic also mentions laxatives used in excess and some supplements among the products that can increase the risk. Reviewing medications does not imply stopping treatments on one's own. The decision must be made with the medical team, especially if a person has recurrent stones or shows changes in their renal function. Prevention requires an adapted strategy for each patient General recommendations include maintaining an adequate urine volume, moderating salt, avoiding excess animal proteins and sugary drinks, maintaining a healthy weight, and controlling diseases such as diabetes, hypertension, gout, and hyperparathyroidism. The National Kidney Foundation and the National Institutes of Health recommend that those who have already had a stone consult about stone analysis and urine studies. Knowing whether the problem is calcium, oxalate, uric acid, struvite, or cystine allows for guidance in prevention. The guidelines of the European Association of Urology propose a broader evaluation for those with recurrences, family history, unusual stones, digestive diseases, urinary abnormalities, a single kidney, or suspicion of a hereditary disorder. The central message is that drinking water is still indispensable, but it is not enough to drink more fluids. Effective prevention requires identifying which factors are altering the urine and acting on them before another stone forms.