- Kidney stones form when certain substances — like calcium, oxalate, or uric acid — bind together in your urine.
- You are more likely to develop kidney stones if it's genetic and runs in the family, or if you have a medical condition like diabetes, obesity, or IBD.
- Risk factors for kidney stones also include an unhealthy diet — high in sodium and low in calcium — or living in the southeastern US.
- This article was medically reviewed by S. Adam Ramin, MD, urologic surgeon and medical director of Urology Cancer Specialists in Los Angeles, California.
Kidney stones are small, painful clumps of minerals that form in your urinary tract. To avoid them, it's important to understand the causes. In fact, your genetics play a big role in whether or not you develop kidney stones, but what you eat and drink, as well as where you live, are also key risk factors. Here's why.
What causes kidney stones?
Kidney stones form when certain minerals and salts in your urine clump together into crystals. As more clump together, the crystals become bigger and turn into stones.
If your urine is more concentrated, these minerals and salts are more likely to be close enough to clump together. If your urine is dilute, these crystals are generally flushed out of the urinary tract before they can become stones, according to Johann Ingimarsson, MD, a urologist at Maine Medical Center.
There are a few different types of kidney stones, and each have specific causes:
- Calcium stones are more likely to form when the concentration of calcium and oxalate in your urine is high. This can be caused by not drinking enough water, or eating too much salt or oxalate-rich foods.
- Struvite stones form because of a urinary tract infection (UTI) caused by bacteria that produce the enzyme urease. Urease breaks down urea, a waste product found in urine, producing ammonia. Magnesium and phosphate, two salts in your urine, are attracted to ammonia, and can bind together, creating crystals and eventually stones, according to Ingimarsson.
- Uric acid stones form when your urine is too acidic. Uric acid, which is found in our blood, crystallizes when pH drops below about 5, says Ingimarsson. Urine is slightly acidic, about a pH of 6, so uric acid dissolves in it. When it drops below a 5, uric acid crystallizes and can clump into kidney stones.
- Cystine stones form in people with certain hereditary disorders that cause them to excrete too much cystine, an amino acid, in their kidneys. When there is a high concentration of cystine amino acids, they are more likely to clump together into stones.
Risk factors for kidney stones
There are also a few common factors that can increase your risk for kidney stones. These include:
Genetics
Not all genetic risk factors for kidney stones are known, but you are more likely to develop kidney stones if you have a family member who also has them. About 40% of stone-formers have a family history of kidney stones.
In fact, two people can eat, drink and behave exactly the same, and one can form kidney stones while the other does not, says Ingimarsson, simply because of their differing genetics.
For instance, about half of people who develop calcium stones have hypercalciuria, or high concentrations of calcium in urine, which is often hereditary, meaning it runs in families.
In the case of cystine stones, you can only develop them if you have a gene mutation that causes cystine to build up in the urine, where it forms stones. However, this is rare, as about 1 in 10,000 people have this condition and less than 3% of kidney stones are cystine stones.
Diet
What you eat and drink can have a big impact on your risk for developing kidney stones. For instance, not drinking enough water will make your urine more concentrated, which increases the likelihood of stone formation, according to Ingimarsson.
Some nutrients can heavily influence the development of kidney stones. Sodium and calcium compete for reabsorption in your kidneys, and if you have a diet high in sodium and low in calcium, it will increase your risk for stones.
It's also helpful to eat calcium and oxalate in the same meal. When eaten together, calcium and oxalate will bind together in your stomach and intestines, preventing stones. Your doctor can also test your urine to see if it has too much oxalate. If it does, cutting back on oxalate-rich foods will help prevent stones.
According to Ingimarsson, about three-quarters of people with kidney stones can manage their risk just by adjusting their diet. Talk with your doctor to determine what dietary changes are best for you.
Location
Where you live also matters. In fact, about 38% of people treated for kidney stones live in the south. The southeast of the US is sometimes referred to as the "Stone Belt" because of this high prevalence.
"People that live further south and especially the south east are at greater risk than people that live further north," says Ingimarsson. "That has to do with both temperature and sun exposure."
Ingimarsson says in hotter temperatures, you sweat more and are more likely to get dehydrated, which increases risk of kidney stones. You are also more likely to get more vitamin D from the sun, and vitamin D helps your body absorb calcium, which could cause it to build up in your urine, putting you at risk for calcium stones.
Medical conditions
Certain medical conditions can also put you at risk for developing kidney stones, including:
- Diabetes. People with type 2 diabetes are 2 to 3 times more likely to get kidney stones, according to a 2013 study published in the journal European Urology. Researchers also found that people with A1C levels higher than 6.5% were 92% more likely to develop stones. People with diabetes have higher levels of urinary oxalate, a key building block of calcium oxalate stones.
- Obesity. A high body mass index (BMI), large waist size, and weight gain all increase your risk for kidney stones. According to a 2020 review published in Reviews in Urology, women with a high BMI had a 1.3-fold increase in kidney stone incidence compared to women with a healthy BMI.
- Inflammatory bowel disease. About 12% to 28% of people with IBD develop kidney stones, which is higher than the prevalence among the general population, according to a 2016 review published in the Journal of Crohn's and Colitis. People with IBD are more likely to have acidic urine, which is a risk factor for uric acid stones.
Takeaways
Knowing the causes and risk factors for kidney stones can help you prevent and manage them. In most cases, Ingimarsson says changing your diet will be enough, although if you have the genetic risk factors or other medical conditions, you may need medication to prevent kidney stones.