Kidney Stones

10 Surprising Facts About Kidney Stones

Originally published May 5, 2020

Last updated April 23, 2024

Reading Time: 4 minutes

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Do you know which part of the country is nicknamed the “Stone Belt”? Find out this and other fascinating facts about these mineral deposits formed by the human body.

You may have heard the oft-cited factoid that kidney stones are as painful as childbirth, but do you know what kidney stones are made of or how to prevent them? Here we’ll look into the strange, surprising and even “shocking” truths about them.

1. More than one type of stone exists.

There are four major types of kidney stones: calcium, struvite, uric acid and cystine. At around 80% of stones, the calcium type is the most common.

Struvite stones sometimes occur after repeated urinary tract infections. Uric acid stones form when urine is too acidic. Cystine stones, which are the rarest, form due to a genetic disorder.

“Calcium and cystine stones are hard,” says Jamal Nabhani, MD, a urologist at Keck Medicine of USC and assistant professor of clinical urology at the Keck School of Medicine of USC. “Struvite stones tend to be softer and larger, sometimes taking up the entire area where urine collects in the kidney. They’re called staghorn stones, because they can look like bull horns.”

Uric acid stones, in particular, can be tricky to diagnose without the right tools. “Although uric acid and calcium stones are often similar in appearance, you can’t see uric acid stones on an X-ray,” Nabhani says. A CT scan is often used for diagnosis.

2. Kidney stones can come in almost any color.

Although kidney stones can have various hues, “most kidney stones have a yellowish appearance,” Nabhani says. “Some have darker interior portions.” The surface of kidney stones may either be smooth or jagged.

3. Kidney stones can be many different sizes.

You may have heard that passing a kidney stone is just as painful as childbirth — and while that may be true in some instances, the pain level depends on the shape and size of the stone.

Kidney stones can be the size of a pea or — although rare — can grow to the size of a golf ball. The largest kidney stone ever recorded, according to Guinness World Records, was just over 5 inches at its widest point. Although very small stones can pass without you even noticing, the larger they are, the more they usually hurt.

It’s estimated that 12% of Americans will develop a kidney stone in their lifetime — and the incidence is rising.

Jamal Nabhani, MD

4. Certain foods can cause stones — but not calcium.

Ironically, although kidney stones are often made up of calcium, they are not caused by calcium intake itself. “Calcium does not usually affect stone formation, unless you are eating much, much more than the recommended daily amount,” Nabhani explains. “We recommend most patients with kidney stones eat the daily recommended amount of calcium.”

So what foods do lead to kidney stones?

“High salt and nondairy animal protein — all types of meat, beef, chicken, fish and pork — are associated with increased stone formation,” Nabhani says.

Salt keeps calcium from being absorbed by the body.

“In addition, foods rich in oxalate, such as nuts, chocolate, spinach and tea, may cause increased stone formation,” he adds.

5. Water can stave off stones.

Salt may lead to stones, but good old H2O can help prevent them.

“Water intake is the single most important dietary risk factor for kidney stone formation,” Nabhani says. “Not drinking enough water is estimated to play a role in 50% of kidney stones. We recommend patients drink enough water to make 2.5 liters (about 10.5 cups) of urine per day, or try to keep their urine clear to very pale yellow.”

6. Kidney stones are more common in summer and in hotter climates.

There’s a reason summer is called kidney stone season.

“Hot weather leads to dehydration, which causes more kidney stones in warmer climates,” Nabhani says. “The southeastern United States is known as the ‘Stone Belt,’ because the incidence of kidney stones is higher in this warm region. Drink your water, especially if it’s hot!”

If you regularly sweat a lot during exercise, such as with hot yoga, be sure to stay hydrated, as well.

7. More than 1 in 10 people will have a kidney stone at some point in their lives.

Unfortunately, kidney stones are common.

“It’s estimated that 12% of Americans will develop a kidney stone in their lifetime — and the incidence is rising,” Nabhani says.

Kidney stones in women are less common than in men.

8. Once you have one stone, you’re more likely to have another.

One kidney stone may not be all you ever have in your lifetime, either. If you’ve had one, you have a 50% risk of developing another in the next five to seven years. So once you experience a stone, it’s especially important to follow your doctor’s recommendations.

9. Kidney stones are linked to other conditions.

One reason the incidence of kidney stones may be rising is that one of the risk factors, obesity, is also on the rise. In addition to obesity, “diabetes, metabolic disturbances, recurrent urinary tract infections and parathyroid disease are associated with kidney stone formation,” Nabhani says.

10. Kidney stones can be treated with shock waves.

One way to treat certain kidney stones is with extracorporeal shock wave lithotripsy, which uses high-energy sound waves as a noninvasive way to break up certain kidney stones so they’re easier to pass. You still need to be given anesthesia before this procedure.

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Tina Donvito
Tina Donvito is a freelance writer covering health, culture, travel and parenting.