Lead author: Kay Shaver, Pharm.D., Assistant Editor
Hypercalciuria is an important and common risk factor for the formation of kidney stones. In fact, about 80% of kidney stones contain calcium and most of these are made up of calcium oxalate. Some calcium stones contain calcium phosphate. A smaller proportion of stones contain uric acid, are struvite stones (caused by urinary tract infections), or are cystine stones. Once a kidney stone forms, there is a 50% probability that
another stone will form within five to seven years without treatment. Initial treatment of recurrent kidney stones generally involves changes in
dietary habits.1-4 It has been thought that decreasing the amount of calcium in the diet reduces the risk of recurrent kidney stones by decreasing the amount of calcium excreted in the urine. However, this idea
has been questioned with the suggestion that calcium may even be protective against kidney stones. This idea has prompted a shift toward
maintaining normal calcium intake and instead emphasizing lower amounts of animal protein and salt. Because there has been a lack of long-term data on whether a low-calcium diet, or a normalcalcium diet that is low in animal protein and salt, is better in preventing recurrent kidney stones, a recent study was done to provide some answers to
the continued debate.
This randomized trial compared the effects of two different diets in 120 men with recurrent calcium oxalate stones and hypercalciuria. Men
were randomly assigned to a low calcium diet or a normal calcium diet. The low calcium diet restricted calcium intake to about 400 mg per day.
The normal calcium diet included about 1,200 mg per day of calcium, but restricted animal protein to 52 grams per day and salt to less than 3 grams
per day. Additional protein or calories came from bread, pasta, vegetables, and fruits instead of meat or fish. Both groups were instructed to avoid large quantities of foods rich in oxalate. Both diets included two to three liters of water per day.Twenty-four hour urine specimens were
collected at baseline, one week after randomization, and at yearly intervals. Urinary volume, sodium, urea, sulfate, calcium excretion,
oxalate excretion, creatinine excretion, and calcium oxalate saturation were measured. Thestudy continued for five years.
In men with hypercalciuria and recurrent calcium oxalate stones, a diet containing normal amounts of calcium but reduced amounts of animal protein and salt, works better to prevent recurrent kidney stones than a low-calcium diet.
The primary outcome was the time to the first recurrence of a symptomatic kidney stone or the radiographic identification of a kidney stone. Secondary outcomes were changes in calcium and oxalate excretion, calcium oxalate product, and relative calcium oxalate saturation. Urinary calcium levels dropped significantly in both groups. However urinary oxalate excretion increased in the men on the low-calcium diet, but decreased in the men on the normal-calcium diet.1
At five years, 12 (20%) men on the normalcalcium diet, and 23 (38%) men on the lowcalcium diet had recurrences of stones. The relative risk of recurrence for the group on the normal-calcium diet was 0.49 compared to the group on the low-calcium diet. After adjustment for baseline characteristics, the relative risk of a recurrence was 0.37 in favor of the normalcalcium,low-protein, low-salt diet.
Counsel patients with recurrent calcium stones to drink plenty of fluids because adequate urine volume is one of the most important factors in at least 2 L per day of urine. Patients will need to drink 2.5 to 3 L of fluids with at least 8 to 12 ounces taken at bedtime. Water is best. This
amount should be increased when fluid losses are increased.2-6
Recommend calcium citrate for postmenopausal women with kidney stone
disease, because in addition to increasing urinary calcium, it also increases the urinary levels of citrate. Suggest taking calcium with meals so it is available to bind intestinal oxalates. Also advise patients to watch their consumption of foods containing oxalate. Some foods high in oxalate
include nuts (walnuts, peanuts, almonds, hazelnuts, etc.), spinach, okra, beets, rhubarb, strawberries, cranberries, soy, wheat bran, brown
rice, chocolate, and cocoa.
1. Borghi L, Schianchi T, Meschi T, et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria.
2. Bushinsky DA. Recurrent hypercalciuric nephrolithiasis-does diet help? NEJM 2002;346:124-125.
3. Goldfarb DS, Coe FL. Prevention of recurrent nephrolithiasis. Am Fam Phys 1999;60:2269-2278.
4. National Institute of Diabetes and Digestive and Kidney Diseases. Kidney stones in adults. National Institutes of Health 2000. NIH publication
no. 00-2495. Available at: www.niddk.nih.gov/ health/kidney/pubs/stonadul/stonadul.htm.
5. Pearle MS. Prevention of nephrolithiasis. Curr Opin Nephrol Hypertens 2001;10:203-209.
6. Morton AR, Iliescu EA, Wilson JWL. Nephrology: Investigation and treatment of recurrent kidney stones. CMAJ 2002;166:213-218.
7. Bihl G, Meyers A. Recurrent renal stone diseaseadvances in pathogenesis and clinical management. Lancet 2001;358:651-656.
8. Jellin JM, Gregory P, Batz F, et al. Pharmacist’s Letter/Prescriber’s Letter Natural Medicines Comprehensive Database. 3rd ed. Stockton, CA:
Therapeutic Research Faculty;2000. Pharmacist’s Letter / Prescriber’s Letter The most practical knowledge in the least time… 3120 West March Lane, P.O. Box 8190, Stockton, CA 95208 TEL (209) 472-2240 FAX (209) 472-2249
Copyright 2002 by Therapeutic Research Center
Last edited by guomanman on Wed 01 Jul 2009, 9:28 am; edited 1 time in total