When a 47-year-old man began fasting for Ramadan, he also added several over-the-counter vitamins and supplements to his daily routine during the COVID-19 pandemic.
Weeks later, he passed his first kidney stone.
Analysis revealed an unusual composition: 60% silica and 40% calcium carbonate, two constituents that rarely make up renal calculi. A review of the supplement labels showed that several products contained silicon dioxide or calcium carbonate as excipients.
The case reported by Ivan Porter, MD, of the Mayo Clinic in Jacksonville, Florida, and colleagues in Annals of Internal Medicine Clinical Cases highlights the value of stone analysis, detailed review of supplement use, and consideration of cultural practices such as fasting that may influence hydration and stone risk.
It also “illustrates the importance of gathering a detailed history of patients’ dietary supplement use and careful monitoring of their current supplements, especially with the increasing prevalence of supplement use and supplement variety,” the authors wrote.
Kidney stones most commonly consist of calcium oxalate mixed with calcium phosphate, which account for about 80% of cases. Struvite (10%), uric acid (9%), and cystine (1%) make up most of the remainder.
Silica stones, however, are extremely rare, representing less than 1% of cases, and are historically linked to chronic ingestion of antacids containing magnesium trisilicate. Calcium carbonate stones are also uncommon, reported in roughly 0.01% to 0.25% of cases. The authors noted that just two prior case reports have linked silica nephrolithiasis to over-the-counter supplement use.
The patient had no significant medical or surgical history other than gastroesophageal reflux and no personal or family history of nephrolithiasis. He was not taking prescription medication but had been taking daily doses of over-the-counter cholecalciferol (vitamin D3) 5,000 IU; vitamin C 1,000 mg; and zinc gluconate 30 mg for more than 6 months. Two months before presentation, he added cyanocobalamin (vitamin B12) 1,000 mcg and magnesium oxide 250 mg for “energy” while fasting for Ramadan, eating once daily in the evening.
Lab testing and a 24-hour urine collection were unremarkable. He was advised to discontinue vitamins C and D and to maintain fluid intake sufficient to produce at least 2.5 liters of urine per day.
Stone analysis confirmed silica and calcium carbonate composition. Review of the supplement labels showed silicon dioxide listed as an inactive ingredient in four products — magnesium oxide, vitamin B12, vitamin C, and zinc gluconate — and calcium carbonate also listed in the zinc supplement.
After discontinuing supplements containing silicon dioxide, the patient had no recurrence.
The authors concluded that the combination of supplements containing silicon dioxide, along with dietary and fluid restriction during Ramadan, likely increased the patient’s risk for developing a silica- and calcium carbonate-containing stone.
“Healthcare providers should be aware of this potential effect of silicon dioxide and increase scrutiny when reviewing patients’ supplement regimens, especially in patients who have increased risk factors to form stones,” the authors wrote.
