Cal­cium sup­ple­ments tied to kid­ney stone risk in study

Daily Trust - - HEALTH -

Peo­ple with a history of kid­ney stones may have a higher risk of re­cur­rence if they use cal­cium sup­ple­ments, a new study finds.

The find­ings, based on records from more than 2,000 pa­tients, add to ev­i­dence link­ing cal­cium sup­ple­ments to kid­ney stone risk.

But re­searchers also said that peo­ple tak­ing cal­cium un­der a doc­tor’s ad­vice should not stop on their own.

“We’re def­i­nitely not ad­vo­cat­ing that peo­ple stop tak­ing cal­cium sup­ple­ments if their doc­tor pre­scribed them for their bone health,” said Christo­pher Lof­tus, the lead re­searcher on the study and an M.D. can­di­date at the Cleve­land Clinic Lerner Col­lege of Medicine.

Lof­tus is sched­uled to present his find­ings next month at the Amer­i­can So­ci­ety of Nephrol­ogy’s an­nual meet­ing in San Diego. Data and con­clu­sions pre­sented at meet­ings should be con­sid­ered pre­lim­i­nary un­til pub­lished in a peer-re­viewed med­i­cal jour­nal.

Kid­ney stones de­velop when high lev­els of crys­tal-form­ing sub­stances -- such as cal­cium, uric acid and a com­pound called ox­alate -- build up in the urine. Most kid­ney stones con­tain cal­cium.

Doc­tors used to ad­vise peo­ple who are “stone for­m­ers” to cut down on their cal­cium in­take, said Dr. Mathew Sorensen, an as­sis­tant pro­fes­sor of urol­ogy at the Univer­sity of Washington in Seat­tle.

And while that “makes sense in­tu­itively,” Sorensen said, re­search since the 1990s has in­di­cated the op­po­site is true: Peo­ple can help lower their risk of kid­ney stone re­cur­rences by get­ting the rec­om­mended amount of cal­cium -- if the cal­cium comes from food.

Cal­cium sup­ple­ments, on the other hand, have been tied to an in­creased risk of kid­ney stones in some stud­ies.

Lof­tus said sup­ple­ments have been linked to higher odds of pass­ing a large stone that causes painful symp­toms. Of­ten, though, small stones pass un­no­ticed, so Lof­tus and his col­leagues looked at whether sup­ple­ment users had a greater risk of form­ing stones at all based on CT scans.

The re­searchers looked at records for more than 2,060 peo­ple with a history of kid­ney stones who un­der­went two CT scans within two years. Al­most 1,500 of those pa­tients were on cal­cium sup­ple­ments, while 417 took vi­ta­min D only. The rest used no sup­ple­ments.

While re­searchers only saw an as­so­ci­a­tion, they found that cal­cium users had a faster rate of new stone for­ma­tion than ei­ther of the other two groups.

Peo­ple may be con­fused by the find­ing, given that cal­cium in food helps pre­vent kid­ney stones, Lof­tus said.

“But there’s a dif­fer­ence be­tween di­etary cal­cium and sup­ple­ments,” he said. “When peo­ple eat cal­cium-con­tain­ing foods, they’re get­ting other nu­tri­ents at the same time.”

Many foods con­tain at least a small amount of the com­pound ox­alate, for ex­am­ple. “The ox­alate in food binds to cal­cium, and you ex­crete it,” Lof­tus said.

Still, some peo­ple might need sup­ple­men­tal cal­cium for the sake of their bone den­sity.

So if a doc­tor has ad­vised you to take cal­cium, do not sim­ply stop on your own, Sorensen said.

“In gen­eral, it’s best to get your cal­cium from food,” Sorensen said. “But if you’re on a sup­ple­ment that’s been pre­scribed to pro­tect your bones, we usu­ally rec­om­mend tak­ing it along with a meal.”

Lof­tus agreed. He added, though, that stone for­m­ers who started us­ing cal­cium sup­ple­ments on their own might want to ask their doc­tor whether that’s re­ally nec­es­sary.

The find­ings come in the wake of a study from New Zealand that con­cluded ex­tra cal­cium -- ei­ther in food or sup­ple­ments -- may not help ag­ing bones at all. That study was pub­lished in the BMJ.

Sorensen of­fered some ad­vice for peo­ple with a history of kid­ney stones: “The most im­por­tant thing,” he said, “is to drink enough fluid ev­ery day.”

That keeps the urine di­luted, and helps flush away ma­te­ri­als that can form stones. Typ­i­cally, stone for­m­ers should aim for 2 to 3 liters of wa­ter and other flu­ids each day, ac­cord­ing to the U.S. Na­tional In­sti­tutes of Health.

Cut­ting back on sodium is also wise, Sorensen said, since sodium causes the kid­neys to ex­crete more cal­cium into the urine.

Stone for­m­ers could also try lim­it­ing their in­take of meat and other an­i­mal pro­teins, Sorensen said, since those foods might con­trib­ute to cal­cium stones by mak­ing the urine more acidic.

Peo­ple who form another kind of kid­ney stone -- uric acid stones -- are of­ten ad­vised to limit their meat in­take to 6 ounces per day, the NIH says.

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