Daily intake of 1200 mg of calcium may help prevent incident and recurrent kidney stones, according to findings from a prospective study published in Mayo Clinic Proceedings. Diets high in potassium were also linked to a lower risk for recurrent kidney stones.
Low dietary calcium and potassium intake were more important predictors of kidney stone formation than low fluid intake, said lead author Api Chewcharat, MD, who was a postdoctoral research fellow at Mayo Clinic Rochester at the time of the study. “This is not to say high fluid intake is not important. We just did not find benefits of increasing fluid intake among those patients with a history of kidney stone formation.” Dr Chewcharat is currently an internal medicine resident at Mount Auburn Hospital in Cambridge, Massachusetts.
The findings are based on questionnaire responses from 411 patients with symptomatic kidney stones (medical record validated) and 384 patients without kidney stones who were seen at Mayo Clinic in Minnesota or Florida between January 1, 2009, and August 31, 2018.
Dietary Risk Factors for Kidney Stones
Dietary risk factors for incident kidney stones included lower levels of calcium, potassium, caffeine, phytate (an antioxidant compound found in whole grains, nuts, and other foods), and fluid intake (<3400 mL/d). Recurrent symptomatic kidney stones were found among 73 patients (18%) during a median follow-up of 4.1 years.
Predictors of symptomatic kidney stone recurrence included lower dietary calcium and lower potassium intake in an analysis that adjusted for body mass index, fluid intake, and energy intake (Table 1). Other variables such as animal protein, phytate, oxalate, sodium, and fiber intake were not significant predictors of recurrent kidney stones in this study. After further adjustment for nondietary risk factors, lower dietary calcium intake remained a predictor of kidney stone recurrence; lower potassium intake only remained a predictor of recurrence among those not taking thiazide diuretics or calcium supplements, the study authors reported.
Table 1. Risk of Recurrent Kidney Stonesa
|Variable||Hazard ratio||P value|
|Fluid intake (mL/d)||1.02||.87|
Table adapted from Chewcharat et al.
“These dietary findings may have particular importance because recommendations for preventing kidney stones have been based primarily on dietary factors associated with first-time rather than recurrent stone formation,” said senior author Andrew Rule, MD, a nephrologist at Mayo Clinic Rochester. “Patients may not be likely to adjust their diet to prevent an incidence of kidney stones but they are more likely to do so if it can help prevent recurrence.”
Tips for Patient Counseling on Kidney Stone Prevention
“In general, dairy foods are the easiest source of calcium and we would suggest 2 or 3 servings of lower fat dairy items such as skim milk, low-fat yogurt, or cheese,” said coauthor John C. Lieske, MD, in an interview. “Items higher in potassium that we would recommend for kidney stone prevention are fruits and vegetables [Table 2]. Many of these also have citrate, which has additional benefit for kidney stone prevention. In general, a good kidney stone diet is also a healthier diet with proportionately more fruits and vegetables and less animal protein and fat.” Dr Lieske is a Mayo Clinic nephrologist and professor of medicine at Mayo Clinic College of Medicine and Science.
Table 2. Selected Foods High in Potassium but Not High in Oxalate
When asked whether calcium supplementation has the same effect as dietary sources of calcium on kidney stone prevention, Dr Lieske said this is not the case. “Studies suggest that while dietary calcium can reduce kidney stone risk, calcium pill supplements probably increase it to some extent. Thus, we would prefer our …. patients get their calcium through natural sources including dairy.”
Potential limitations of the findings are that some patients with incident kidney stones may have changed their diet in response to the kidney stone episode but before their study visit. Documentation of dietary advice was recorded in only 20% of cases and was typically limited to a recommendation to increase water intake, the study authors noted. Also, the data may be limited by recall bias among the study participants.
The authors hope to be able to have more data to better personalize dietary recommendations based on stone composition and each patient’s metabolic profile, Dr Chewcharat said in an accompanying video.
Chewcharat A, Thongprayoon C, Vaughan LE, et al. Dietary risk factors for incident and recurrent symptomatic kidney stones. Mayo Clin Proc. 2022;97(8):1437-1448. doi:10.1016/j.mayocp.2022.04.01
Diets higher in calcium and potassium may help prevent recurrent symptomatic kidney stones, Mayo Clinic study finds. News Release. Mayo Clinic. July 29, 2022. Accessed August, 8, 2022. https://newsnetwork.mayoclinic.org/discussion/diets-higher-in-calcium-and-potassium-may-help-prevent-recurrent-symptomatic-kidney-stones-mayo-clinic-study-finds/