From the Guidelines
No, patients with calcium oxalate kidney stones should not avoid calcium, as recent evidence suggests that a higher calcium diet is associated with a reduced risk of stone formation 1. In fact, they should consume adequate dietary calcium (about 1000-1200 mg daily) from food sources. Restricting calcium can actually increase stone risk because dietary calcium binds to oxalate in the gut, preventing its absorption and subsequent excretion in urine.
Key Recommendations
- Patients should limit sodium (to less than 2300 mg daily) and animal protein, while maintaining normal calcium intake 1.
- They should also reduce consumption of high-oxalate foods like spinach, rhubarb, nuts, and chocolate.
- Adequate hydration is crucial—patients should drink enough fluid to produce at least 2-2.5 liters of urine daily.
- The timing of calcium intake matters too; consuming calcium with meals is most effective for binding dietary oxalate, as supported by a 5-year randomized controlled clinical trial 1.
- However, it's essential to note that the impact of supplemental calcium is different from dietary calcium, and patients with calcium urolithiasis who wish to continue calcium supplementation should collect 24-h urine samples on and off the supplement to assess the risk of stone formation 1.
Rationale
The rationale behind these recommendations is based on the mechanism of action of calcium in binding dietary oxalate in the gut, thereby reducing oxalate absorption and urinary excretion 1. Additionally, a higher calcium diet has been associated with a reduced risk of stone formation in several large prospective observational studies in men and women 1.
Clinical Considerations
It's crucial to consider the individual patient's needs and circumstances, such as those with enteric hyperoxaluria and high levels of urinary oxalate, who may benefit from more restrictive oxalate diets and higher calcium intakes, including supplements, specifically timed with meals 1. However, the most recent and highest quality study 1 supports the recommendation to maintain normal calcium intake and limit oxalate-rich foods.
From the FDA Drug Label
A moderate calcium restriction (400-800 mg/day) was imposed on patients with hypercalciuria
- Key point: The drug label mentions a moderate calcium restriction for patients with hypercalciuria.
- Answer: Patients with calcium oxalate should restrict calcium intake to 400-800 mg/day if they have hypercalciuria, as stated in the study 2.
From the Research
Calcium Intake for Patients with Calcium Oxalate Stones
- Patients with calcium oxalate stones do not necessarily need to avoid calcium entirely, as calcium intake can actually help reduce the risk of stone formation 3, 4.
- A dietary calcium intake of 600 to 800 mg/day is recommended to help reduce urinary supersaturation of calcium oxalate 3.
- However, patients with idiopathic hypercalciuria, a common cause of calcium oxalate stones, may need to reduce their calcium intake to below 200 mg/24 hr with thiazide treatment 3.
Treatment Options for Calcium Oxalate Stones
- Thiazide diuretics and potassium citrate (K-Cit) are commonly used to prevent calcium stone recurrence, and have been shown to be effective in reducing urine calcium and supersaturation 5, 6.
- K-Cit has been shown to increase urinary citrate levels and reduce calcium excretion in patients with calcium oxalate stones and hypercalciuria 6.
- However, the effectiveness of K-Cit in preventing calcium phosphate stone formation is unclear, and may not confer the same benefits as it does for calcium oxalate stone formers 5.
Dietary Recommendations for Preventing Stone Recurrence
- A dietary regimen low in salt and protein, rich in calcium and magnesium, and coupled with adequate fluid intake is recommended to prevent kidney stone recurrence 4.
- However, the evidence for specific dietary changes is limited, and more research is needed to quantify the risks of diet in stone formation 7.