Novel and Emerging Strategies
Hypercalciuria (high urine calcium concentration) is associated with both calcium kidney stones and bone loss (Xu 2013; Arrabal-Polo, Sierra Giron-Prieto 2013). Some researchers are beginning to explore the effect of a class of osteoporosis medications called bisphosphonates, such as alendronate (Fosamax), risedronate (Actonel), and ibandronate (Boniva), on calcium kidney stone risk (Grover 2013). These medications help keep urine calcium concentrations from rising by reducing bone breakdown and calcium loss (Bianchi 2010).
In one trial, 16 people placed on experimental bed rest for 3 weeks (in order to increase urinary calcium excretion by causing bone breakdown) and treated with 20 mg per day of the bisphosphonate alendronate had lower urine calcium concentrations, and lower calcium oxalate and calcium phosphate saturations, compared with placebo (Ruml 1995). In another trial, 70 individuals with recurrent calcium kidney stones, high urine calcium concentration, and bone loss were treated with either 70 mg per week of alendronate or 70 mg per week of alendronate plus 50 mg per day of the diuretic hydrochlorothiazide. After two years of treatment, an increase in bone mineral density and a decrease in urine calcium concentration was seen with both medication regimens, but the group treated with alendronate plus hydrochlorothiazide had more improvement than the group treated with alendronate alone (Arrabal-Polo, Arias-Santiago 2013).
While these findings are intriguing, they do not clearly establish whether alendronate or other bisphosphonates can prevent calcium kidney stone formation; in addition, some questions remain about the long-term safety of bisphosphonate use (Suresh 2014).
Many people with recurrent kidney stones get them only on one side, leading some researchers to examine whether sleep position can predict the side on which stones occur. In a study of 110 unilateral (one-sided) kidney stone formers, 93 were found to sleep predominantly on one side, and of these, 71 (76%) slept on the same side as that of their stones (Shekarriz 2001). In a study in unilateral stone formers, 88% of participants with right-sided kidney stones slept right side down, and 62% of participants with left-sided stones slept left side down (Ziaee 2008).
Oxalobacter formigenes (Probiotic)
Oxalobacter formigenes (O. formigenes) is a bacterium found in the human digestive tract. It digests and metabolizes oxalate, preventing high urine oxalate and calcium oxalate kidney stones (Mogna 2014; Knight 2013). Several studies have found that antibiotic use can lead to the loss of O. formigenes colonies (Knight 2013).
One study found that patients with greater O. formigenes colonization had significantly lower urine oxalate levels (Kwak 2003). Stool cultures from recurrent calcium oxalate stone formers show that they are only about half as likely to have colonies of this bacterium compared with non-stone formers, and those with O. formigenes colonies have as much as 70% lower odds of calcium oxalate stone recurrence (Knight 2013; Kaufman 2008).
In a rodent model of severe hyperoxaluria, administration of O. formigenes as a probiotic supplement reduced urinary oxalate in just two days (Sidhu 2001). In a randomized controlled trial in 42 patients with the rare genetic condition primary hyperoxaluria, oral supplementation with O. formigenes resulted in more than twice the reduction of oxalate relative to urine creatinine compared to placebo. In those with the highest baseline oxalate concentrations, the reduction of urine oxalate was more than four times that of placebo (Hoppe 2011).
O. formigenes has been developed into a biopharmaceutical preparation and is not available as a dietary supplement at this time.