Nephrolithiasis, commonly known as kidney stones, is a condition where hard mineral deposits form inside the kidneys and can cause severe pain as they travel through the urinary system. These stones affect millions of people worldwide, with patterns and risk factors that can help you understand and potentially avoid this painful condition.
How Common Are Kidney Stones?
Kidney stones have become increasingly common in recent decades. In the United States, approximately 1 in 11 people will experience a kidney stone at some point in their lifetime. This represents a significant increase from the 1970s, when only about 4% of Americans had kidney stones. Today, that number has risen to around 10% of the population, showing a clear upward trend that has concerned healthcare professionals.[2][7]
The condition does not affect everyone equally. Men are affected about twice as often as women, and the problem tends to strike around midlife. The annual incidence of kidney stones is approximately eight cases per 1,000 adults, with the condition peaking in people in their 30s and 40s. Geographic location also plays a role—people living in hot climates, particularly in the southeastern United States in what’s known as the “Stone Belt” extending from the southeastern United States to northern Australia, experience higher rates of kidney stones. This is likely because warm weather increases the risk of dehydration, which contributes to stone formation.[3][7]
Non-Hispanic white people appear to develop kidney stones more frequently than other ethnic groups. Economic factors also come into play, with persons of lower socioeconomic status showing higher rates of the condition. These demographic patterns suggest that both genetic and environmental factors contribute to who develops kidney stones.[7]
What Causes Kidney Stones to Form?
Kidney stones develop when certain substances in your urine become concentrated enough to form crystals. Your urine normally contains minerals, acids, and other substances like calcium, sodium, oxalate (a naturally occurring compound found in many foods), and uric acid (a waste product from protein breakdown). When you have too many particles of these substances in your urine and not enough liquid to dilute them, they can begin to stick together, forming crystals or stones. This process can take months or even years.[1][3]
Most kidney stones—about 75% to 85%—are made primarily of calcium, either combined with oxalate or phosphate. Calcium oxalate stones are the single most common type. Another type, uric acid stones, form when urine becomes too acidic. Struvite stones (made of magnesium ammonium phosphate) develop as a result of bacterial infections in the urinary tract. Finally, cystine stones are rare and result from an inherited genetic condition called cystinuria, which causes the kidneys to release too much of a specific amino acid.[2][3]
Stones can also form due to low levels of substances that normally prevent crystal formation. For example, citrate is a natural inhibitor of stone formation found in urine. When citrate levels are too low, stones are more likely to develop. Similarly, excessive acidity in the urine creates an environment where certain types of stones form more easily.[2]
The fundamental issue is an imbalance in urine composition. When urine becomes concentrated—often due to decreased fluid intake—the ratio of stone-forming substances to liquid shifts dramatically, allowing crystals to form. Anatomic features that cause urine to remain in the kidneys longer than normal can also contribute to stone formation by giving crystals more time to grow.[2]
Who Is at Higher Risk?
Several factors can increase your likelihood of developing kidney stones. Understanding these risk factors can help you take steps to reduce your chances of forming stones.[3]
Not drinking enough fluids is one of the most significant risk factors. When you don’t consume adequate water, your urine becomes more concentrated, creating ideal conditions for crystals to form. People who live in hot climates or work in hot environments need even more fluids because sweating reduces the amount of urine their bodies produce.[3][7]
Your diet plays a crucial role in stone formation. Eating large amounts of animal protein—such as beef, poultry, pork, eggs, and fish—can contribute to uric acid stone formation. Foods high in sodium (salt) increase the amount of calcium in your urine, raising the risk of calcium-based stones. Excessive intake of foods high in oxalate, such as spinach, beets, nuts, and chocolate, can also promote stone formation. Consuming too many sugars, particularly fructose and sucrose, has been linked to increased stone risk.[3][7]
Having a family history of kidney stones significantly increases your risk, suggesting a genetic component to the condition. If a parent or sibling has had kidney stones, you’re more likely to develop them yourself.[3]
Certain health conditions raise the risk of kidney stones. These include obesity, which has been strongly associated with stone formation, likely due to changes in urine chemistry. People with high blood pressure, gout, nonalcoholic fatty liver disease, and diabetes face elevated risks. Those who have had gastrointestinal surgery, including gastric bypass surgery, may experience changes in digestion and calcium absorption that promote stone formation.[3][7]
Some medications and supplements can also increase stone risk. Taking high doses of vitamin C supplements may contribute to oxalate stone formation. Certain medications prescribed for other conditions can alter urine chemistry in ways that promote stones. If you have blockages in your urinary tract, urine can pool and concentrate, providing more opportunity for crystals to form.[3]
Recognizing the Symptoms
The symptoms of kidney stones can range from completely silent to excruciating. Small stones, sometimes as tiny as a grain of sand, may pass through your urinary system without causing any noticeable discomfort. You might never even know they were there. However, larger stones can cause some of the most intense pain a person can experience.[3]
The most characteristic symptom is severe pain, often described as worse than childbirth, broken bones, or surgery. This pain, known as renal colic, typically occurs when a stone moves from the kidney into the ureter (the tube that carries urine from the kidney to the bladder), causing a blockage. The pain usually begins suddenly without warning and is located in the lower back, belly, or side. Many people describe the pain as starting in the flank area and radiating toward the groin. The pain often comes in waves, getting worse and then better, because it results from the ureter stretching and contracting as it tries to push the stone through.[3][4][7]
Pain is frequently accompanied by nausea and vomiting. Many people with kidney stones feel generally unwell and may experience fever or chills, particularly if an infection is present. Blood in the urine is another common symptom—your urine may appear pink, red, or brown. You might also experience pain or burning when you urinate, an urgent need to urinate frequently, an inability to urinate despite feeling the urge, or cloudy or foul-smelling urine.[3]
The pain often shifts as the stone moves through the urinary tract. When it travels down the ureter toward the bladder, you may feel frequent urination, pressure in the bladder, or pain in the groin area. Once the stone reaches the bladder, the severe pain typically subsides almost immediately, and the stone usually passes out of the body relatively quickly through the urethra during urination.[18]
Preventing Kidney Stones
The good news is that many kidney stones can be prevented through lifestyle and dietary changes. These preventive measures are especially important if you’ve already had one stone, since recurrence is common without intervention.[7]
The single most important preventive measure is drinking enough fluids, particularly water. Healthcare professionals typically recommend drinking enough to produce 2 to 2.5 liters of urine each day—about 8 to 10 glasses of water. Research shows that people who produce this amount of urine daily are 50% less likely to develop kidney stones than those who produce less. Your urine color provides a simple guide: pale or clear urine indicates good hydration, while dark yellow urine is a sign you need to drink more. In hot weather or if you exercise, you’ll need even more fluids to compensate for fluid lost through sweating.[7][17][18]
Adding citrus to your diet can help prevent stones. Lemons, limes, oranges, and grapefruits contain citrate, which binds to calcium and helps block stone formation. Drinking half a cup of lemon juice concentrate diluted in water each day, or simply adding fresh lemon juice to your drinking water, may reduce stone recurrence.[17][18]
Dietary modifications play a crucial role in prevention. Despite what you might expect, reducing calcium intake is not generally recommended and may actually increase stone risk. Instead, aim for a normal amount of calcium from food sources like yogurt, milk, cheese, and leafy greens. These calcium-rich foods help by binding oxalate in your intestines, preventing it from being absorbed and ending up in your urine where it could form stones.[18][19]
Limiting sodium (salt) is important because high sodium levels cause your body to excrete more calcium in urine, promoting stone formation. Aim for less than 2,300 milligrams of sodium daily by avoiding processed foods, Chinese and Mexican restaurant food, tomato juice, and regular canned foods. Look for low-salt or unsalted alternatives.[19]
Moderating protein intake, especially from animal sources, can help prevent uric acid stones. Choose lean meats and consider incorporating more plant-based proteins like beans, lentils, tofu, and nuts into your diet. Reducing consumption of foods high in oxalate—such as spinach, beets, nuts, chocolate, and certain teas—may be recommended if you have calcium oxalate stones, though you should discuss this with your healthcare provider first.[19]
Maintaining a healthy weight through balanced diet and regular physical activity reduces stone risk. Exercise not only helps with weight management but also promotes overall kidney health by enhancing blood flow to the kidneys. Quitting smoking is another important step, as smoking has been linked to increased kidney stone risk.[3]
How Kidney Stones Affect the Body
Understanding what happens in your body when kidney stones form and move helps explain why they cause such intense symptoms. The kidneys are located toward the back of the upper abdomen, where they filter waste and excess fluid from blood to produce urine. Urine flows from each kidney through a narrow tube called a ureter into the bladder, where it’s stored until you urinate. Finally, urine leaves the body through the urethra.[1]
When stones form in the kidney itself, they may cause no symptoms at all, especially if they remain small and stationary. Problems arise when a stone begins to move. As it travels from the kidney into the ureter, it can become lodged in this narrow tube. The ureter is only about 3 to 4 millimeters in diameter, so even relatively small stones can cause a blockage.[4]
The blockage prevents urine from flowing normally from the kidney to the bladder. This causes urine to back up into the kidney, a condition called hydronephrosis, which stretches the kidney and the ureter. The severe, cramping pain of renal colic results primarily from this stretching and from spasms of the ureter as it tries to push the stone through. The pain comes in waves because the ureter contracts rhythmically in an attempt to move the obstruction.[4][7]
When a stone blocks urine flow, it limits the kidney’s ability to filter waste from the blood. While a single episode typically doesn’t cause permanent kidney damage, recurrent stones can injure the tubular epithelial cells (specialized cells lining the kidney’s filtering system), leading to gradual loss of kidney function over time. This is particularly concerning for people with only one functioning kidney, pre-existing kidney disease, or other risk factors for kidney damage.[2][4]
Stones can also damage the lining of the urinary tract as they move through, which is why blood in the urine is a common symptom. Additionally, blocked urine flow creates an environment where bacteria can multiply, increasing the risk of urinary tract infections. If infection develops in a blocked kidney—a serious condition called pyonephrosis—it can lead to severe complications and requires urgent treatment.[2]
The biochemical process of stone formation begins with supersaturation of urine with stone-forming substances. Think of it like adding sugar to tea: at a certain point, the liquid can’t dissolve any more sugar, and crystals begin to form. The same principle applies in urine. When concentrations of calcium, oxalate, uric acid, or other substances exceed the urine’s capacity to keep them dissolved, crystallization begins. These tiny crystals can then stick together and grow, eventually forming visible stones.[2]
Your body has natural defense mechanisms against stone formation. Citrate and other inhibitors in urine normally prevent crystals from forming or binding together. Adequate urine volume dilutes stone-forming substances. When these protective mechanisms fail—whether due to dehydration, dietary factors, metabolic abnormalities, or genetic conditions—stones can develop. Understanding this process helps explain why increasing fluid intake and modifying diet can effectively prevent stones from forming in the first place.[2]
