Kidney stones may be increasing among both men and women in the US, a new study says.
The study, published Monday in the journal Mayo Clinic Proceedings, looks at the prevalence of kidney stones over a period of almost three decades -- from 1984 to 2012 -- among more than 10,000 residents of Minnesota.
Kidney stones increased more than fourfold among women and more than twofold among men, it found.
Young women ages 18 to 39 had the highest increase in cases, jumping from 62 to 252 cases (per 100,000 person-years) from 1984 to 2012. One person-year is a year lived by each participant for the duration of the study.
"What we're seeing is an interesting combination of things; certainly, they've gone up quite a bit both in men and women," said Dr. John Lieske, a professor of medicine at the Mayo Clinic in Rochester, Minnesota, and a lead author of the study.
"The absolute increase has been similar, but because women started out quite a bit lower 30 years ago, their proportion increases quite a bit more."
Kidney stones are relatively common, affecting around 10% of people at some point in their lives. They are caused by solid pieces of material that crystallize in the kidney, ureters or bladder due to a number of genetic and environmental factors, Lieske said.
"A lot of it is related to genetics," he said. "Too much calcium in the urine is certainly a factor in many of these patients but not all of them, and then there's other things that come into play related to diet and not drinking enough fluids."
Kidney stones are notoriously painful and can cause "renal colic" that comes in waves and spreads from the lower back to the inner thigh, according to Dr. Ralph Clayman, a professor of urology at the University of California, Irvine and an expert on kidney stone disease.
"They call it male childbirth," said Clayman, who was not involved in the study. "It's extremely, excruciatingly painful. Renal colic is very painful, and a lot of times, people need opioids in order to manage the pain."
In order to confirm a diagnosis of kidney stones, physicians may use imaging techniques such as ultrasound or computed tomography (CT) scans. An increase in the overall use of CT scans over the past 30 years -- which are more likely to pick up the stones -- may be partially responsible for the increased rate of kidney stone diagnoses, Lieske said.
"Some amount of this increase in stone events is related to more CT scans being done," he said. "But that's not the whole story."
According to Clayman, there were over 80 million CT scans performed in the US in 2016, up from 2.7 million in 1995.
"You're going to pick up all these small, asymptomatic stones," he said. "They just need to be followed, but basically if you know you've got it, maybe that's enough of a stimulus that you're going to change your lifestyle."
Most kidney stones are made up of calcium salts, often calcium oxalate or calcium phosphate. The prevalence of both types of stones increased over the past three decades, according to the study. Calcium oxalate accounted for nearly 75% of all stones with a known composition.
Oxalate is a naturally occurring substance found in many foods including beets, chocolate, tea and nuts.
"A lot of people who get these are susceptible because of their genetics, and then perhaps on top of that is an added risk from their diet," Lieske said.
But the prevalence of other types of stones, such as struvite and uric acid stones, did not appear to significantly increase over the past three decades. Struvite stones are often associated with urinary tract infections, while uric acid stones are linked to gout and the consumption of animal protein.
Staying hydrated and reducing sodium intake can help prevent most types of kidney stones. According to the Mayo Clinic, drinking as much as 2 to 3 quarts of water per day can help remove small stones -- less than 3 millimeters in diameter -- by flushing out the urinary system.
"Nothing, nothing, trumps fluids," Clayman said. "If you're drinking 3 quarts a day and making 2½ quarts of urine a day, that's the best way you can protect or defend either against getting kidney stones or, if you've had them, defend against getting them again."
For larger stones, however, more extensive treatment may be necessary, Lieske said. Such treatments include using sound waves to break the stones or surgery to remove them through a small incision in the lower back.
Lieske cautions that the results of the new study may not be generalizable to all Americans.
"Kidney stones as a group are more common in whites in particular, which was about 90% of the population" that the researchers studied, he added. "We wouldn't be able to comment as much on some of the other ethnic groups, though. I think that would be an open question."